Post by thread:[EE]: RF modules

Hi, I'm designing a network of devices that uses a shared wireless medium. Messages will be sent to specific nodes using an address unique to each device. Each node will also sense the presence and addresses of all other devices within transmission range. I was going to do this by having each device transmit an announcement at regular intervals (OK, somewhat regular; I realize that I'll have to avoid collisions). I want to make the cost per node as low as possible, and requirements for range and throughput are very low. (A few tens of metres and a few hundred bps minimum). I was looking at transceivers using 315MHz and 433MHz frequencies costing about $25 US in small quantities, which would be acceptable. I read somewhere that unlicensed users of those frequencies are prohibited from sending continuous data or regular periodic data. Would my application violate those requirements? I get the impression that the 900MHz range is less restricted, but those modules seem to be far more expensive. Can anyone point me to the authoritative document that details the limitations? I'm in Canada, but I expect that our regulations are similar to those in the US. This is a student project, so certification for retail sale is not an issue, but I'd like to avoid building something that is blatantly illegal or harmful to others. :) Thanks in advance, Greg -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

Hi- I have used the 433MHz pairs. Work quite well. They also have some 916 MHz pairs, and some transievers. Here's their pricelist, in US$: LP link 900 931.9375Mhz POCSAG Receiver 25.00 LP link xxx Customer made freq. 140 932Mhz POCSAG Receiver 25.00 RF900CLP Base 900MHz Voice transceiver 40ch Base 5V 12.00 RF900CLP Remote 900MHz Voice Transceiver 40ch Remote 3.6V 12.00 RF900DV Base 900MHz Data & Voice Transceiver 16ch Base @28.8K 27.00 RF900DV Remote 900MHz Data & Voice Transceiver 16ch Remote @28.8K 27.00 RF2400DV Base 2.4Ghz Data & Voice Transceiver 16ch Base @28.8K 31.00 RF2400DV Remote 2.4Ghz Data & Voice Transceiver 16ch Remote @28.8K 31.00 CCD-52 w/mic + Rx Complete set of 2.4Ghz CCD w/mic, Rx video/audio, batt. 220.00 CCD-52 w/o mic + Rx Complete set of 2.4Ghz CCD w/o mic,Rx video/audio,batt. 210.00 CCD-52 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) 140.00 CCD-51 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) 136.00 TLP315 RF ASK Transmitter at 315Mhz 4.80 TLP315A RF ASK Transmitter at 315Mhz ( Smaller ) 4.80 TLP418 RF ASK Transmitter at 418Mhz 4.80 TLP418A RF ASK Transmitter at 418Mhz ( Smaller ) 4.80 TLP433.92 RF ASK Transmitter at 433.92Mhz 4.80 TLP433.92A RF ASK Transmitter at 433.92Mhz ( Smaller ) 4.80 TLP916-ASK RF ASK Transmitter at 916.5Mhz 7.00 TLP916-FSK RF FSK Transmitter at 916.5Mhz 9.00 RLP315 RF ASK Receiver at 315Mhz - LC Type 4.80 RLP315A RF ASK Receiver at 315Mhz - SAW Type 9.50 RLP418 RF ASK Receiver at 418Mhz - LC Type 4.80 RLP418A RF ASK Receiver at 418Mhz - SAW Type 9.50 RLP433.92 RF ASK Receiver at 433.92Mhz - LC Type 4.80 RLP433.92A RF ASK Receiver at 433.92Mhz - SAW Type 9.50 RLP916-ASK RF ASK Receiver at 916.5Mhz 13.00 RLP916-FSK RF FSK Receiver at 916.5Mhz 14.00 TLP4XX- 2W * RF FSK & FM Transmitter UHF 0.5 - 2 Watt 25.00 David Ann & David Scott wrote: {Quote hidden}> Maybe the Laipac modules will work for you? They're in Toronto. > A receiver/transmitter pair is less than $10US. I've used these > with success (garage door type application). > > I'm a bit puzzled why I haven't seen more on this list about > these modules. They seem to be a useful item for their low > cost. Can anyone comment? > > G Brigley wrote on 5/11/02 5:04 pm: > >Hi, > > > >I'm designing a network of > >devices that uses a shared > >wireless medium.... > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Thanks everyone, I hadn't heard of Laipac. Their low-end modules are pretty competitive, and their $27 900MHz transceivers seem pretty attractive too. I'm not sure now which way to go. I get the impression that the 315 and 433 MHz modules are usually used for "Press a button, close a relay" type applications. Maybe it's not worth trying to coax a multipoint data network out of them, even if throughput requirements are low. If I did go this route, would I be able to control a seperate receiver and transmitter with a pic, or should I be looking only at integrated transceivers? I might yet switch to 900MHz. The extra range could come in handy. And maybe there'd be app notes more similar to what I'm doing. Greg On Mon, 13 May 2002, David P. Harris wrote: {Quote hidden}> Hi- > I have used the 433MHz pairs. Work quite well. They also have some 916 > MHz pairs, and some transievers. Here's their pricelist, in US$: > > LP link 900 931.9375Mhz POCSAG Receiver 25.00 > LP link xxx Customer made freq. 140 932Mhz POCSAG Receiver 25.00 > RF900CLP Base 900MHz Voice transceiver 40ch Base 5V 12.00 > RF900CLP Remote 900MHz Voice Transceiver 40ch Remote 3.6V 12.00 > RF900DV Base 900MHz Data & Voice Transceiver 16ch Base @28.8K 27.00 > RF900DV Remote 900MHz Data & Voice Transceiver 16ch Remote @28.8K 27.00 > RF2400DV Base 2.4Ghz Data & Voice Transceiver 16ch Base @28.8K 31.00 > RF2400DV Remote 2.4Ghz Data & Voice Transceiver 16ch Remote @28.8K 31.00 > CCD-52 w/mic + Rx Complete set of 2.4Ghz CCD w/mic, Rx video/audio, batt. > 220.00 > CCD-52 w/o mic + Rx Complete set of 2.4Ghz CCD w/o mic,Rx > video/audio,batt. 210.00 > CCD-52 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) > 140.00 > CCD-51 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) > 136.00 > TLP315 RF ASK Transmitter at 315Mhz 4.80 > TLP315A RF ASK Transmitter at 315Mhz ( Smaller ) 4.80 > TLP418 RF ASK Transmitter at 418Mhz 4.80 > TLP418A RF ASK Transmitter at 418Mhz ( Smaller ) 4.80 > TLP433.92 RF ASK Transmitter at 433.92Mhz 4.80 > TLP433.92A RF ASK Transmitter at 433.92Mhz ( Smaller ) 4.80 > TLP916-ASK RF ASK Transmitter at 916.5Mhz 7.00 > TLP916-FSK RF FSK Transmitter at 916.5Mhz 9.00 > RLP315 RF ASK Receiver at 315Mhz - LC Type 4.80 > RLP315A RF ASK Receiver at 315Mhz - SAW Type 9.50 > RLP418 RF ASK Receiver at 418Mhz - LC Type 4.80 > RLP418A RF ASK Receiver at 418Mhz - SAW Type 9.50 > RLP433.92 RF ASK Receiver at 433.92Mhz - LC Type 4.80 > RLP433.92A RF ASK Receiver at 433.92Mhz - SAW Type 9.50 > RLP916-ASK RF ASK Receiver at 916.5Mhz 13.00 > RLP916-FSK RF FSK Receiver at 916.5Mhz 14.00 > TLP4XX- 2W * RF FSK & FM Transmitter UHF 0.5 - 2 Watt 25.00 > > David > > Ann & David Scott wrote: > > > Maybe the Laipac modules will work for you? They're in Toronto. > > A receiver/transmitter pair is less than $10US. I've used these > > with success (garage door type application). > > > > I'm a bit puzzled why I haven't seen more on this list about > > these modules. They seem to be a useful item for their low > > cost. Can anyone comment? > > > > G Brigley wrote on 5/11/02 5:04 pm: > > >Hi, > > > > > >I'm designing a network of > > >devices that uses a shared > > >wireless medium.... > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

You may want to check out: http://www.linxtechnologies.com/ldocs/f_applic.html I've already gone down the path of creating simple data links between laipac's 433Mhz modules. Works well, multiple nodes, machester encoding, simple collision detaction, stuff like that. Then I read the above document about FCC regulations. Seems that my application is non-compliant (I was transmitting temp/time and other general home automation information). It seems as though the 900MHz range is better (in that it seems less restricted), but too expensive for my hobbying around needs. Kevin G Brigley wrote: {Quote hidden}> > Thanks everyone, > > I hadn't heard of Laipac. Their low-end modules are pretty competitive, > and their $27 900MHz transceivers seem pretty attractive too. > > I'm not sure now which way to go. > > I get the impression that the 315 and 433 MHz modules are usually used for > "Press a button, close a relay" type applications. Maybe it's not worth > trying to coax a multipoint data network out of them, even if throughput > requirements are low. If I did go this route, would I be able to control > a seperate receiver and transmitter with a pic, or should I be looking > only at integrated transceivers? > > I might yet switch to 900MHz. The extra range could come in handy. And > maybe there'd be app notes more similar to what I'm doing. > > Greg > > On Mon, 13 May 2002, David P. Harris wrote: > > > Hi- > > I have used the 433MHz pairs. Work quite well. They also have some 916 > > MHz pairs, and some transievers. Here's their pricelist, in US$: > > > > LP link 900 931.9375Mhz POCSAG Receiver 25.00 > > LP link xxx Customer made freq. 140 932Mhz POCSAG Receiver 25.00 > > RF900CLP Base 900MHz Voice transceiver 40ch Base 5V 12.00 > > RF900CLP Remote 900MHz Voice Transceiver 40ch Remote 3.6V 12.00 > > RF900DV Base 900MHz Data & Voice Transceiver 16ch Base @28.8K 27.00 > > RF900DV Remote 900MHz Data & Voice Transceiver 16ch Remote @28.8K 27.00 > > RF2400DV Base 2.4Ghz Data & Voice Transceiver 16ch Base @28.8K 31.00 > > RF2400DV Remote 2.4Ghz Data & Voice Transceiver 16ch Remote @28.8K 31.00 > > CCD-52 w/mic + Rx Complete set of 2.4Ghz CCD w/mic, Rx video/audio, batt. > > 220.00 > > CCD-52 w/o mic + Rx Complete set of 2.4Ghz CCD w/o mic,Rx > > video/audio,batt. 210.00 > > CCD-52 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) > > 140.00 > > CCD-51 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) > > 136.00 > > TLP315 RF ASK Transmitter at 315Mhz 4.80 > > TLP315A RF ASK Transmitter at 315Mhz ( Smaller ) 4.80 > > TLP418 RF ASK Transmitter at 418Mhz 4.80 > > TLP418A RF ASK Transmitter at 418Mhz ( Smaller ) 4.80 > > TLP433.92 RF ASK Transmitter at 433.92Mhz 4.80 > > TLP433.92A RF ASK Transmitter at 433.92Mhz ( Smaller ) 4.80 > > TLP916-ASK RF ASK Transmitter at 916.5Mhz 7.00 > > TLP916-FSK RF FSK Transmitter at 916.5Mhz 9.00 > > RLP315 RF ASK Receiver at 315Mhz - LC Type 4.80 > > RLP315A RF ASK Receiver at 315Mhz - SAW Type 9.50 > > RLP418 RF ASK Receiver at 418Mhz - LC Type 4.80 > > RLP418A RF ASK Receiver at 418Mhz - SAW Type 9.50 > > RLP433.92 RF ASK Receiver at 433.92Mhz - LC Type 4.80 > > RLP433.92A RF ASK Receiver at 433.92Mhz - SAW Type 9.50 > > RLP916-ASK RF ASK Receiver at 916.5Mhz 13.00 > > RLP916-FSK RF FSK Receiver at 916.5Mhz 14.00 > > TLP4XX- 2W * RF FSK & FM Transmitter UHF 0.5 - 2 Watt 25.00 > > > > David > > > > Ann & David Scott wrote: > > > > > Maybe the Laipac modules will work for you? They're in Toronto. > > > A receiver/transmitter pair is less than $10US. I've used these > > > with success (garage door type application). > > > > > > I'm a bit puzzled why I haven't seen more on this list about > > > these modules. They seem to be a useful item for their low > > > cost. Can anyone comment? > > > > > > G Brigley wrote on 5/11/02 5:04 pm: > > > >Hi, > > > > > > > >I'm designing a network of > > > >devices that uses a shared > > > >wireless medium.... > > > > > > -- > > > http://www.piclist.com hint: The list server can filter out subtopics > > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> > Tell us how you went about doing collision detection. > I did say it was simple, all I do is check to see if there is traffic already > being transmitted before I try to transmit. I check by just sampling the > received RF data for a few bits worth of time. If I can receive some data > (variations in the bit stream), I just wait for the max packet length (all my > packets are the same size) and try again, checking for data before each send > attempt. That with a CRC16 is what I mean by simple. Good first start. A significant improvement is obtained by backing off for a random period AFTER the end of the packet being sent and then sending if still free. This allows multiple would be senders to compete randomly for the free channel. If you don't do this and their are several stations waiting to send they will ALL see the channel free at once and ALL try and send at once and ALL collide and then ALL retry again in due course. Worst case, if response times are closely matched you could spend most of your time in collisions. This basic scheme is historically referred to as "Aloha". Sending on fixed method length boundaries with random backoff is modified Aloha. (Name, not surprisingly, from early Uni of Hawaii radio net). Random backoff to allow multi station competition is a standard feature of most collision detection schemes. Note that it should be as truly random as you can reasonably get to prevent some stations hogging the circuit. If you all drop into lockstep and compete together repeatedly you can also be in trouble. Russell McMahon -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Hey Russell (king of the neat [OT]: posts), Cool, this actually had crossed my mind. One of the remote device types are clocks with a DS1820 for temperature. The original idea was just to have a remote temp sensor, but I thought adding a clock function might make it more useful to have some small box plugged into various rooms. I thought that after a power outage (and return), all the devices would attempt at the same time to 'phone home'. My solution (though not yet tried), was to use the 'deviveID' of each unit. Each one is 'uniquely' identified so the master can track temp results. I was going to use this number to affect the retry timing. I was also thinking about some sort of passed token scheme. The 'master' would poll the remotes granting them permission to transmit. This would involve me configuring the master for each new device though. Or maybe the nodes could pass the token around (more configuration...) Not sure. I don't have a lot of data to push around, time, temp, lighting/mp3 control and status, ... all fairly low bandwidth, but I would like it to be fairly reliable. I'd like to look into self correcting streams too, sounds way over my head, but cool. I figured I could try a few different schemes since this is really is just for fun. Now if I only could find some RF modules that were cheap AND legal for this application... As always advice is always welcome. This list is great, I really appreciate the posters and the folks who maintain it. Thanks, Kevin Russell McMahon wrote: {Quote hidden}> A significant improvement is obtained by backing off for a random period > AFTER the end of the packet being sent and then sending if still free. This > allows multiple would be senders to compete randomly for the free channel. > If you don't do this and their are several stations waiting to send they > will ALL see the channel free at once and ALL try and send at once and ALL > collide and then ALL retry again in due course. Worst case, if response > times are closely matched you could spend most of your time in collisions. > This basic scheme is historically referred to as "Aloha". Sending on fixed > method length boundaries with random backoff is modified Aloha. (Name, not > surprisingly, from early Uni of Hawaii radio net). > > Random backoff to allow multi station competition is a standard feature of > most collision detection schemes. Note that it should be as truly random as > you can reasonably get to prevent some stations hogging the circuit. If you > all drop into lockstep and compete together repeatedly you can also be in > trouble. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> Sounds simple enough. Thanks, I'm shooting for simple. > So after your max packet length time do you check > again to see if someone else is still transmitting or just use the CRC > to validate that the message wasn't stepped on by someone else. I always check for an existing transmission before I start transmitting a packet, even on the retries. I don't check in between bytes of the packet. > What you are doing is all perfectly reasonable BTW. You have only the > time between the last time you check to see if someone was on the air > and when you start that someone else could also start. Since that's at > the most perhaps a bit time or two, you can be sure that whoever > stepped on your message will also find start looking after a message. Not sure what you mean by, 'also find start looking'. But my thinking was that if someone started transmitting in that three bit windows neither of us would get ACK'ed and we'd both try again. Now making it evident that Russell's suggestion is a good one. > I take it then that you send an acknowledge back with for every message? Yes. The sender has a fixed time to wait for the ACK, else it tries again. I try ten times (arbitrary number) before I give up an flash an LED. > And, out of curiosity, how do you determine if someone is transmitting? The idle state of the protocol is 0, so if I see any 1's I assume someone is transmitting. I over sample for the time it takes to transmit three bits. If I get any hits during that time, I go into retry mode. Thanks, Kevin -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> > > What you are doing is all perfectly reasonable BTW. You > have only the > > time between the last time you check to see if someone was > on the air > > and when you start that someone else could also start. > Since that's at > > the most perhaps a bit time or two, you can be sure that whoever > > stepped on your message will also find start looking after > a message. > > Not sure what you mean by, 'also find start looking'. But my > thinking was that > if someone started transmitting in that three bit windows > neither of us would > get ACK'ed and we'd both try again. Now making it evident > that Russell's > suggestion is a good one. Darn Outlook XP. Deleted a whole line in there. What I meant to say was that whoever stepped on your message will also find that the bus may still be busy if they start looking at the end of the message. Didn't make a lot of sense then and in some ways still doesn't. 8-( {Quote hidden}> > > And, out of curiosity, how do you determine if someone is > transmitting? > > The idle state of the protocol is 0, so if I see any 1's I > assume someone is > transmitting. I over sample for the time it takes to > transmit three bits. If I > get any hits during that time, I go into retry mode. So the signal is ASK or FM? John -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

John Dammeyer wrote: <snip> > Darn Outlook XP. Deleted a whole line in there. What I meant to say > was that whoever stepped on your message will also find that the bus may > still be busy if they start looking at the end of the message. Didn't > make a lot of sense then and in some ways still doesn't. 8-( Does looking for transmission at the end of messages provide more information? I guess I'd know a little sooner that I got stepped on. {Quote hidden}> > > And, out of curiosity, how do you determine if someone is > > transmitting? > > > > The idle state of the protocol is 0, so if I see any 1's I > > assume someone is > > transmitting. I over sample for the time it takes to > > transmit three bits. If I > > get any hits during that time, I go into retry mode. > > So the signal is ASK or FM? Um, yeah. ASK, but I only think that from looking at Laipac's website. I've seen acronymns such as ASK, FSK, SAW, FM, ... but frankly have no idea what they mean. I just bought a couple of modules from Rentron and started to push some data through. Can you shed some light? Thanks, Kevin -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> > Does looking for transmission at the end of messages provide > more information? > I guess I'd know a little sooner that I got stepped on. Only if you can predict what the end of frame looks like. If you insist on 4 logic 1's at the end of the message then you can look after your done and if there are 1's you don't have to wait for a timeout but can start n bit times after the 1's finish. Just remember, that it takes time for the transmitter to turn off and the receiver to turn on. {Quote hidden}> > > > So the signal is ASK or FM? > > Um, yeah. ASK, but I only think that from looking at > Laipac's website. I've > seen acronymns such as ASK, FSK, SAW, FM, ... but frankly > have no idea what they > mean. I just bought a couple of modules from Rentron and > started to push some > data through. > > Can you shed some light? For the experts out there, forgive my non-technical layman's description. OOK. On Off Keying. Like Morse Code. Transmitter totally on or totally off. ASK. Amplitude Shift Keying. Low power is 0, high power is 1. FM. Frequency modulation. Always the same power, but two different frequencies for 1 and 0. SAW is a type of filter. Spread Spectrum means that the frequency is changing in a pseudo random pattern within each bit with the idea that at least one of the frequencies will get through. There are two problems with RF. Signal strength varies inversely as the square of the distance and there is a term called "noise floor" which is the signal the receiver sees when there isn't anyone transmitting. If your transmitter is too far away from the receiver for example the signal level from the transmitter will still be there but might be buried under the noise floor. Alternatively, you may have lots of signal but something else nearby has more signal and hides yours. Since someone else's signal is noise to you the concept of noise floor still holds. The second problem is more of an irritation. If you are familiar with AC sine waves you probably understand that if you mix two identical frequency signals of equal but opposite phase you end up with no signal because the two cancel each other out. The same happens in RF except now it's reflections that do this. Your signal from the transmitter may take several different paths to reach you and since the paths have different lengths the signals arrive at different times; in essence, out of phase. If it's enough to cause a 100% attenuation it's called a NULL. Change frequency by 1 MHz and the null moves to a different location all other things being equal. That's why the frequency hopping spread spectrum stuff works so well. At least part of the bit won't be at a frequency which is in a null. Hope that helps a bit. John Dammeyer {Quote hidden}> > Thanks, > Kevin > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> Hey Russell (king of the neat [OT]: posts), Flattery will get you somewhere :-) > 'phone home'. My solution (though not yet tried), was to use the 'deviveID' of > each unit. Each one is 'uniquely' identified so the master can track temp > results. I was going to use this number to affect the retry timing. > > I was also thinking about some sort of passed token scheme. The 'master' would > poll the remotes granting them permission to transmit. This would involve me > configuring the master for each new device though. Or maybe the nodes could > pass the token around (more configuration...) A scheme I was going to try but never used (customer decided not to proceed befor ewe got that far) was for a new node to be assigned a default address eg 255. The master would poll this address at a low rate and any new devices would acknowledge and be assigned a "real" adress. If collisons occurred here a random backoff was used. (The proposed system was extremely bus intensive with a large number of slaves and good utilisation of the bus was vital. Slaves with data to send could ack with a single bit in the right timeslot to allow the master to ignore them or service them as appropriate. The system was conceptually full duplex (and very wierd half duplex in actual implementation due to specialist environment) with slaves only hearing the master and the master hearing all slaves but not itself). > I'd like to look into self correcting streams too, sounds way over > my head, but cool.. > I figured I could try a few different schemes since this is really is just for > fun. Self correcting (aka FEC = forward error correcting) is indeed fun but usually very computationally or memory intensive - not a good match to most PICs probably. Lookup "Reed Solomon" for ideas. For this sort of system odds are that basic error checing (parity, Hamming, CRC, ...) is good enough with an ARQ system (blocks are ACK'd or NACK'd or ignored if indecipherable and are repeated in the latter 2 cases). Russell McMahon -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

I'm currently looking at the Laipac modules and a bunch of others for a telemetry system. I've been around the block on searching and laipac definitely has the cheapest units for what they will bring. The 1200' range and size of the unit is very attractive. However, at initial glance, they do not have a lot of documentation on the web. I was sent the datasheet for the 900MHz 27$ module yesterday and it was really brief. I am very temped to order them and give it a shot. The other option was Linx modules which have a lot of support and documentation, including example applications. Anyone used Laipac's 900MHz modules? Regards, Michael > [Original Message] > From: G Brigley <.....gobrigleKILLspam.....ENGMAIL.UWATERLOO.CA> > To: <EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU> > Date: 5/13/02 10:21:52 AM {Quote hidden}> Subject: Re: [EE]: RF modules > > Thanks everyone, > > I hadn't heard of Laipac. Their low-end modules are pretty competitive, > and their $27 900MHz transceivers seem pretty attractive too. > > I'm not sure now which way to go. > > I get the impression that the 315 and 433 MHz modules are usually used for > "Press a button, close a relay" type applications. Maybe it's not worth > trying to coax a multipoint data network out of them, even if throughput > requirements are low. If I did go this route, would I be able to control > a seperate receiver and transmitter with a pic, or should I be looking > only at integrated transceivers? > > I might yet switch to 900MHz. The extra range could come in handy. And > maybe there'd be app notes more similar to what I'm doing. > > Greg > > On Mon, 13 May 2002, David P. Harris wrote: > > > Hi- > > I have used the 433MHz pairs. Work quite well. They also have some 916 > > MHz pairs, and some transievers. Here's their pricelist, in US$: > > > > LP link 900 931.9375Mhz POCSAG Receiver 25.00 > > LP link xxx Customer made freq. 140 932Mhz POCSAG Receiver 25.00 > > RF900CLP Base 900MHz Voice transceiver 40ch Base 5V 12.00 > > RF900CLP Remote 900MHz Voice Transceiver 40ch Remote 3.6V 12.00 > > RF900DV Base 900MHz Data & Voice Transceiver 16ch Base @28.8K 27.00 > > RF900DV Remote 900MHz Data & Voice Transceiver 16ch Remote @28.8K 27.00 > > RF2400DV Base 2.4Ghz Data & Voice Transceiver 16ch Base @28.8K 31.00 > > RF2400DV Remote 2.4Ghz Data & Voice Transceiver 16ch Remote @28.8K 31.00 > > CCD-52 w/mic + Rx Complete set of 2.4Ghz CCD w/mic, Rx video/audio, batt. > > 220.00 > > CCD-52 w/o mic + Rx Complete set of 2.4Ghz CCD w/o mic,Rx > > video/audio,batt. 210.00 > > CCD-52 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) > > 140.00 > > CCD-51 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) > > 136.00 > > TLP315 RF ASK Transmitter at 315Mhz 4.80 > > TLP315A RF ASK Transmitter at 315Mhz ( Smaller ) 4.80 > > TLP418 RF ASK Transmitter at 418Mhz 4.80 > > TLP418A RF ASK Transmitter at 418Mhz ( Smaller ) 4.80 > > TLP433.92 RF ASK Transmitter at 433.92Mhz 4.80 > > TLP433.92A RF ASK Transmitter at 433.92Mhz ( Smaller ) 4.80 > > TLP916-ASK RF ASK Transmitter at 916.5Mhz 7.00 > > TLP916-FSK RF FSK Transmitter at 916.5Mhz 9.00 > > RLP315 RF ASK Receiver at 315Mhz - LC Type 4.80 > > RLP315A RF ASK Receiver at 315Mhz - SAW Type 9.50 > > RLP418 RF ASK Receiver at 418Mhz - LC Type 4.80 > > RLP418A RF ASK Receiver at 418Mhz - SAW Type 9.50 > > RLP433.92 RF ASK Receiver at 433.92Mhz - LC Type 4.80 > > RLP433.92A RF ASK Receiver at 433.92Mhz - SAW Type 9.50 > > RLP916-ASK RF ASK Receiver at 916.5Mhz 13.00 > > RLP916-FSK RF FSK Receiver at 916.5Mhz 14.00 > > TLP4XX- 2W * RF FSK & FM Transmitter UHF 0.5 - 2 Watt 25.00 > > > > David > > > > Ann & David Scott wrote: > > > > > Maybe the Laipac modules will work for you? They're in Toronto. > > > A receiver/transmitter pair is less than $10US. I've used these > > > with success (garage door type application). > > > > > > I'm a bit puzzled why I haven't seen more on this list about > > > these modules. They seem to be a useful item for their low > > > cost. Can anyone comment? > > > > > > G Brigley wrote on 5/11/02 5:04 pm: > > > >Hi, > > > > > > > >I'm designing a network of > > > >devices that uses a shared > > > >wireless medium.... > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Guys, Recent discussion has peaked my interest especially since the relatively cheap Laipac modules were introduced. I'm looking at using the TLP434 modules outside in an open field. I'd like to get the most range that I can. At least 150' but would be nice to get to ~600'. Anyway, I have no experience with RF, specifically the antenna. Can someone shed some light on this? How do you know how long a wire to use? Do you just use a piece of wire? What gauge? Can it still have the insulation on it? What is "loop", "whip" style that I see listed on the Laipac page? Is the antenna different for the transmitter and receiver? As you can see, I'm a novice at this antenna stuff. I don't really want a whole bunch of analytical antenna design mumbo jumbo. Be nice if someone would say something like "Ya, just connect a piece of 24AWG wire to the antenna that's about 3" long and that'll give you pretty good reception". Something like that. Thanks, Gary At 03:17 PM 5/13/2002 -0400, Kevin Olalde wrote: {Quote hidden}>You may want to check out: > >http://www.linxtechnologies.com/ldocs/f_applic.html > >I've already gone down the path of creating simple data links between laipac's >433Mhz modules. Works well, multiple nodes, machester encoding, simple >collision detaction, stuff like that. > >Then I read the above document about FCC regulations. Seems that my >application >is non-compliant (I was transmitting temp/time and other general home >automation >information). > >It seems as though the 900MHz range is better (in that it seems less >restricted), but too expensive for my hobbying around needs. > >Kevin > >G Brigley wrote: > > > > Thanks everyone, > > > > I hadn't heard of Laipac. Their low-end modules are pretty competitive, > > and their $27 900MHz transceivers seem pretty attractive too. > > > > I'm not sure now which way to go. > > > > I get the impression that the 315 and 433 MHz modules are usually used for > > "Press a button, close a relay" type applications. Maybe it's not worth > > trying to coax a multipoint data network out of them, even if throughput > > requirements are low. If I did go this route, would I be able to control > > a seperate receiver and transmitter with a pic, or should I be looking > > only at integrated transceivers? > > > > I might yet switch to 900MHz. The extra range could come in handy. And > > maybe there'd be app notes more similar to what I'm doing. > > > > Greg > > > > On Mon, 13 May 2002, David P. Harris wrote: > > > > > Hi- > > > I have used the 433MHz pairs. Work quite well. They also have some 916 > > > MHz pairs, and some transievers. Here's their pricelist, in US$: > > > > > > LP link 900 931.9375Mhz POCSAG Receiver 25.00 > > > LP link xxx Customer made freq. 140 932Mhz POCSAG Receiver 25.00 > > > RF900CLP Base 900MHz Voice transceiver 40ch Base 5V 12.00 > > > RF900CLP Remote 900MHz Voice Transceiver 40ch Remote 3.6V 12.00 > > > RF900DV Base 900MHz Data & Voice Transceiver 16ch Base @28.8K 27.00 > > > RF900DV Remote 900MHz Data & Voice Transceiver 16ch Remote @28.8K 27.00 > > > RF2400DV Base 2.4Ghz Data & Voice Transceiver 16ch Base @28.8K 31.00 > > > RF2400DV Remote 2.4Ghz Data & Voice Transceiver 16ch Remote @28.8K 31.00 > > > CCD-52 w/mic + Rx Complete set of 2.4Ghz CCD w/mic, Rx video/audio, batt. > > > 220.00 > > > CCD-52 w/o mic + Rx Complete set of 2.4Ghz CCD w/o mic,Rx > > > video/audio,batt. 210.00 > > > CCD-52 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) > > > 140.00 > > > CCD-51 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) > > > 136.00 > > > TLP315 RF ASK Transmitter at 315Mhz 4.80 > > > TLP315A RF ASK Transmitter at 315Mhz ( Smaller ) 4.80 > > > TLP418 RF ASK Transmitter at 418Mhz 4.80 > > > TLP418A RF ASK Transmitter at 418Mhz ( Smaller ) 4.80 > > > TLP433.92 RF ASK Transmitter at 433.92Mhz 4.80 > > > TLP433.92A RF ASK Transmitter at 433.92Mhz ( Smaller ) 4.80 > > > TLP916-ASK RF ASK Transmitter at 916.5Mhz 7.00 > > > TLP916-FSK RF FSK Transmitter at 916.5Mhz 9.00 > > > RLP315 RF ASK Receiver at 315Mhz - LC Type 4.80 > > > RLP315A RF ASK Receiver at 315Mhz - SAW Type 9.50 > > > RLP418 RF ASK Receiver at 418Mhz - LC Type 4.80 > > > RLP418A RF ASK Receiver at 418Mhz - SAW Type 9.50 > > > RLP433.92 RF ASK Receiver at 433.92Mhz - LC Type 4.80 > > > RLP433.92A RF ASK Receiver at 433.92Mhz - SAW Type 9.50 > > > RLP916-ASK RF ASK Receiver at 916.5Mhz 13.00 > > > RLP916-FSK RF FSK Receiver at 916.5Mhz 14.00 > > > TLP4XX- 2W * RF FSK & FM Transmitter UHF 0.5 - 2 Watt 25.00 > > > > > > David > > > > > > Ann & David Scott wrote: > > > > > > > Maybe the Laipac modules will work for you? They're in Toronto. > > > > A receiver/transmitter pair is less than $10US. I've used these > > > > with success (garage door type application). > > > > > > > > I'm a bit puzzled why I haven't seen more on this list about > > > > these modules. They seem to be a useful item for their low > > > > cost. Can anyone comment? > > > > > > > > G Brigley wrote on 5/11/02 5:04 pm: > > > > >Hi, > > > > > > > > > >I'm designing a network of > > > > >devices that uses a shared > > > > >wireless medium.... > > > > > > > > -- > > > > http://www.piclist.com hint: The list server can filter out subtopics > > > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > -- > > > http://www.piclist.com hint: The list server can filter out subtopics > > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics Gary Neal Research Assistant - Drivetrain Technology Center Applied Research Laboratory - Penn State University PO Box 30 Research Building West North Atherton Street State College, PA 16801 814-863-5468 (phone) 814-863-6185 (fax) -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Antennas are a whole subject in itself. They come in all sizes, shapes, and colors. Simply put, a monopole is a simple antenna which is a single piece of wire, usually called a whip in most forms. Antennas should be tailored to the frequency being used. Moreover, they need to be tuned to listen in for a specfic frequency's wavelength or a function of it. Depending on the frequency and type of usage, there are different antennas for different applications. Higher frequencies tend to be more directional as you go up in freq which creates the need for antennas that can transmit or listen in all or specified directions. A 1/4 wave antenna works fine for most applications. Use this relation to figure this out required length: C= lamda x V, where c= 3 x 10^8, V = frequency, and lambda = wavelength. For example, a 900MHz device would need: 3 x 10^8 / 900 x 10^6 = .333 meter wavelength. Dividing this by 4, only a 8.25 cm long antenna is needed. This can be a loop, coil, etc. Linx technologies has a good primer on antennas. http://www.linxtechnologies.com/ldocs/pdfs/AN00500.pdf Also, they have an antenna site. http://www.antennafactor.com/adocs/f_prod.html Hope this helps, Michael > [Original Message] > From: Gary Neal <KILLspamgln103KILLspamPSU.EDU> > To: <RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU> > Date: 5/14/02 8:57:12 AM {Quote hidden}> Subject: Re: [EE]: RF modules > > Guys, > > Recent discussion has peaked my interest especially since the > relatively cheap Laipac modules were introduced. I'm looking at using the > TLP434 modules outside in an open field. I'd like to get the most range > that I can. At least 150' but would be nice to get to ~600'. > Anyway, I have no experience with RF, specifically the > antenna. Can someone shed some light on this? How do you know how long a > wire to use? Do you just use a piece of wire? What gauge? Can it still > have the insulation on it? What is "loop", "whip" style that I see listed > on the Laipac page? Is the antenna different for the transmitter and receiver? > As you can see, I'm a novice at this antenna stuff. I don't > really want a whole bunch of analytical antenna design mumbo jumbo. Be > nice if someone would say something like "Ya, just connect a piece of 24AWG > wire to the antenna that's about 3" long and that'll give you pretty good > reception". Something like that. > > Thanks, > > Gary -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Thanks, Great info! So you could take that 8.25cm wire and wrap it into a coil and it would be just about as effective as leaving it straight? Can I use just normal stranded ~24AWG hookup wire for the antenna? Does the insulation around the wire matter? Thanks, Gary At 09:25 AM 5/14/2002 -0700, you wrote: {Quote hidden}>Antennas are a whole subject in itself. They come in all sizes, shapes, and >colors. Simply put, a monopole is a simple antenna which is a single piece >of wire, usually called a whip in most forms. Antennas should be tailored to >the frequency being used. Moreover, they need to be tuned to listen in for a >specfic frequency's wavelength or a function of it. Depending on the >frequency and type of usage, there are different antennas for different >applications. Higher frequencies tend to be more directional as you go up in >freq which creates the need for antennas that can transmit or listen in all >or specified directions. > >A 1/4 wave antenna works fine for most applications. Use this relation to >figure this out required length: C= lamda x V, where c= 3 x 10^8, V = >frequency, and lambda = wavelength. > >For example, a 900MHz device would need: > >3 x 10^8 / 900 x 10^6 = .333 meter wavelength. Dividing this by 4, only a >8.25 cm long antenna is needed. This can be a loop, coil, etc. > >Linx technologies has a good primer on antennas. >http://www.linxtechnologies.com/ldocs/pdfs/AN00500.pdf > >Also, they have an antenna site. >http://www.antennafactor.com/adocs/f_prod.html > >Hope this helps, >Michael > > > [Original Message] > > From: Gary Neal <spamBeGonegln103spamBeGonePSU.EDU> > > To: <TakeThisOuTPICLISTEraseMEspam_OUTMITVMA.MIT.EDU> > > Date: 5/14/02 8:57:12 AM > > Subject: Re: [EE]: RF modules > > > > Guys, > > > > Recent discussion has peaked my interest especially since the > > relatively cheap Laipac modules were introduced. I'm looking at using the > > TLP434 modules outside in an open field. I'd like to get the most range > > that I can. At least 150' but would be nice to get to ~600'. > > Anyway, I have no experience with RF, specifically the > > antenna. Can someone shed some light on this? How do you know how long a > > wire to use? Do you just use a piece of wire? What gauge? Can it still > > have the insulation on it? What is "loop", "whip" style that I see listed > > on the Laipac page? Is the antenna different for the transmitter and >receiver? > > As you can see, I'm a novice at this antenna stuff. I don't > > really want a whole bunch of analytical antenna design mumbo jumbo. Be > > nice if someone would say something like "Ya, just connect a piece of >24AWG > > wire to the antenna that's about 3" long and that'll give you pretty good > > reception". Something like that. > > > > Thanks, > > > > Gary Gary Neal Research Assistant - Drivetrain Technology Center Applied Research Laboratory - Penn State University PO Box 30 Research Building West North Atherton Street State College, PA 16801 814-863-5468 (phone) 814-863-6185 (fax) -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

What is the definition of a telemetry system? I've seen that term a lot while I've been shopping for modules. I don't know what your application is, but I was looking at the $27 Laipac module until I realized that they sell two versions; a base and a remote, and that multiple remote units can't talk directly to one another. Neither can multiple base units. However, a base can talk to multiple remote units in full-duplex, and a remote can talk to multiple base units in full duplex. I can think of lots of applications where this would be perfect, but mine isn't one of them. Greg On Tue, 14 May 2002, Michael Luvara wrote: {Quote hidden}> I'm currently looking at the Laipac modules and a bunch of others for a telemetry system. I've been around the block on searching and laipac definitely has the cheapest units for what they will bring. The 1200' range and size of the unit is very attractive. However, at initial glance, they do not have a lot of documentation on the web. I was sent the datasheet for the 900MHz 27$ module yesterday and it was really brief. I am very temped to order them and give it a shot. The other option was Linx modules which have a lot of support and documentation, including example applications. > > Anyone used Laipac's 900MHz modules? > > Regards, > Michael > > > [Original Message] > > From: G Brigley <gobrigleEraseME.....ENGMAIL.UWATERLOO.CA> > > To: <EraseMEPICLISTMITVMA.MIT.EDU> > > Date: 5/13/02 10:21:52 AM > > Subject: Re: [EE]: RF modules > > > > Thanks everyone, > > > > > > I hadn't heard of Laipac. Their low-end modules are pretty competitive, > > > and their $27 900MHz transceivers seem pretty attractive too. > > > > > > I'm not sure now which way to go. > > > > > > I get the impression that the 315 and 433 MHz modules are usually used for > > > "Press a button, close a relay" type applications. Maybe it's not worth > > > trying to coax a multipoint data network out of them, even if throughput > > > requirements are low. If I did go this route, would I be able to control > > > a seperate receiver and transmitter with a pic, or should I be looking > > > only at integrated transceivers? > > > > > > I might yet switch to 900MHz. The extra range could come in handy. And > > > maybe there'd be app notes more similar to what I'm doing. > > > > > > Greg > > > > > > On Mon, 13 May 2002, David P. Harris wrote: > > > > > > > Hi- > > > > I have used the 433MHz pairs. Work quite well. They also have some 916 > > > > MHz pairs, and some transievers. Here's their pricelist, in US$: > > > > > > > > LP link 900 931.9375Mhz POCSAG Receiver 25.00 > > > > LP link xxx Customer made freq. 140 932Mhz POCSAG Receiver 25.00 > > > > RF900CLP Base 900MHz Voice transceiver 40ch Base 5V 12.00 > > > > RF900CLP Remote 900MHz Voice Transceiver 40ch Remote 3.6V 12.00 > > > > RF900DV Base 900MHz Data & Voice Transceiver 16ch Base @28.8K 27.00 > > > > RF900DV Remote 900MHz Data & Voice Transceiver 16ch Remote @28.8K 27.00 > > > > RF2400DV Base 2.4Ghz Data & Voice Transceiver 16ch Base @28.8K 31.00 > > > > RF2400DV Remote 2.4Ghz Data & Voice Transceiver 16ch Remote @28.8K 31.00 > > > > CCD-52 w/mic + Rx Complete set of 2.4Ghz CCD w/mic, Rx video/audio, batt. > > > > 220.00 > > > > CCD-52 w/o mic + Rx Complete set of 2.4Ghz CCD w/o mic,Rx > > > > video/audio,batt. 210.00 > > > > CCD-52 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) > > > > 140.00 > > > > CCD-51 w/mic CCD 2.4Ghz CCD color w/mic ( avail. Freq. 2412/32/52/72) > > > > 136.00 > > > > TLP315 RF ASK Transmitter at 315Mhz 4.80 > > > > TLP315A RF ASK Transmitter at 315Mhz ( Smaller ) 4.80 > > > > TLP418 RF ASK Transmitter at 418Mhz 4.80 > > > > TLP418A RF ASK Transmitter at 418Mhz ( Smaller ) 4.80 > > > > TLP433.92 RF ASK Transmitter at 433.92Mhz 4.80 > > > > TLP433.92A RF ASK Transmitter at 433.92Mhz ( Smaller ) 4.80 > > > > TLP916-ASK RF ASK Transmitter at 916.5Mhz 7.00 > > > > TLP916-FSK RF FSK Transmitter at 916.5Mhz 9.00 > > > > RLP315 RF ASK Receiver at 315Mhz - LC Type 4.80 > > > > RLP315A RF ASK Receiver at 315Mhz - SAW Type 9.50 > > > > RLP418 RF ASK Receiver at 418Mhz - LC Type 4.80 > > > > RLP418A RF ASK Receiver at 418Mhz - SAW Type 9.50 > > > > RLP433.92 RF ASK Receiver at 433.92Mhz - LC Type 4.80 > > > > RLP433.92A RF ASK Receiver at 433.92Mhz - SAW Type 9.50 > > > > RLP916-ASK RF ASK Receiver at 916.5Mhz 13.00 > > > > RLP916-FSK RF FSK Receiver at 916.5Mhz 14.00 > > > > TLP4XX- 2W * RF FSK & FM Transmitter UHF 0.5 - 2 Watt 25.00 > > > > > > > > David > > > > > > > > Ann & David Scott wrote: > > > > > > > > > Maybe the Laipac modules will work for you? They're in Toronto. > > > > > A receiver/transmitter pair is less than $10US. I've used these > > > > > with success (garage door type application). > > > > > > > > > > I'm a bit puzzled why I haven't seen more on this list about > > > > > these modules. They seem to be a useful item for their low > > > > > cost. Can anyone comment? > > > > > > > > > > G Brigley wrote on 5/11/02 5:04 pm: > > > > > >Hi, > > > > > > > > > > > >I'm designing a network of > > > > > >devices that uses a shared > > > > > >wireless medium.... > > > > > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Telemetry is generally measuring data from something and sending it to a remote area to analyze it. I am developing a unit for radio cotnrolled aircraft which measures certain characteristics and sends it to a laptop in real time, for display on a "virtual instrument panel". As for antenna orientation, design, they are all good for different things. Take a look at the aarl handbook as suggested by another list member. The linx technology app note is good too for starters. Coils, loops, etc run into certain constraints, like matching, etc. Most of the time these layouts are used for space reasons, and can give lesser results than a simple monopole. Michael > [Original Message] > From: G Brigley <RemoveMEgobrigleEraseMEEraseMEengmail.uwaterloo.ca> > To: Michael Luvara <RemoveMEmluvaraspam_OUTKILLspamearthlink.net> > Cc: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU> > Date: 5/14/02 10:18:22 AM {Quote hidden}> Subject: Re: [EE]: RF Modules > > What is the definition of a telemetry system? I've seen that term a lot > while I've been shopping for modules. > > I don't know what your application is, but I was looking at the $27 Laipac > module until I realized that they sell two versions; a base and a remote, > and that multiple remote units can't talk directly to one another. > Neither can multiple base units. However, a base can talk to multiple > remote units in full-duplex, and a remote can talk to multiple base units > in full duplex. I can think of lots of applications where this would be > perfect, but mine isn't one of them. > > Greg > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Hi- Except you have 434 MHz modules, so you want: 3x10^8/434x10^6 = 0.69, so you want a 0.69/4 = 0.173 meter = 17.3 cm 1/4 wave whip. I think it needs to be straight. Hey, my 12 cm piece of wire seems to work fine, gues I should extend it. David Gary Neal wrote: {Quote hidden}> Thanks, > > Great info! > > So you could take that 8.25cm wire and wrap it into a coil and it would be > just about as effective as leaving it straight? > > Can I use just normal stranded ~24AWG hookup wire for the antenna? Does > the insulation around the wire matter? > > Thanks, > > Gary > > At 09:25 AM 5/14/2002 -0700, you wrote: > >Antennas are a whole subject in itself. They come in all sizes, shapes, and > >colors. Simply put, a monopole is a simple antenna which is a single piece > >of wire, usually called a whip in most forms. Antennas should be tailored to > >the frequency being used. Moreover, they need to be tuned to listen in for a > >specfic frequency's wavelength or a function of it. Depending on the > >frequency and type of usage, there are different antennas for different > >applications. Higher frequencies tend to be more directional as you go up in > >freq which creates the need for antennas that can transmit or listen in all > >or specified directions. > > > >A 1/4 wave antenna works fine for most applications. Use this relation to > >figure this out required length: C= lamda x V, where c= 3 x 10^8, V = > >frequency, and lambda = wavelength. > > > >For example, a 900MHz device would need: > > > >3 x 10^8 / 900 x 10^6 = .333 meter wavelength. Dividing this by 4, only a > >8.25 cm long antenna is needed. This can be a loop, coil, etc. > > > >Linx technologies has a good primer on antennas. > >www.linxtechnologies.com/ldocs/pdfs/AN00500.pdf > > > >Also, they have an antenna site. > >http://www.antennafactor.com/adocs/f_prod.html > > > >Hope this helps, > >Michael > > > > > [Original Message] > > > From: Gary Neal <EraseMEgln103spamspamBeGonePSU.EDU> > > > To: <RemoveMEPICLISTKILLspamMITVMA.MIT.EDU> > > > Date: 5/14/02 8:57:12 AM > > > Subject: Re: [EE]: RF modules > > > > > > Guys, > > > > > > Recent discussion has peaked my interest especially since the > > > relatively cheap Laipac modules were introduced. I'm looking at using the > > > TLP434 modules outside in an open field. I'd like to get the most range > > > that I can. At least 150' but would be nice to get to ~600'. > > > Anyway, I have no experience with RF, specifically the > > > antenna. Can someone shed some light on this? How do you know how long a > > > wire to use? Do you just use a piece of wire? What gauge? Can it still > > > have the insulation on it? What is "loop", "whip" style that I see listed > > > on the Laipac page? Is the antenna different for the transmitter and > >receiver? > > > As you can see, I'm a novice at this antenna stuff. I don't > > > really want a whole bunch of analytical antenna design mumbo jumbo. Be > > > nice if someone would say something like "Ya, just connect a piece of > >24AWG > > > wire to the antenna that's about 3" long and that'll give you pretty good > > > reception". Something like that. > > > > > > Thanks, > > > > > > Gary > > Gary Neal > Research Assistant - Drivetrain Technology Center > Applied Research Laboratory - Penn State University > PO Box 30 > Research Building West > North Atherton Street > State College, PA 16801 > 814-863-5468 (phone) > 814-863-6185 (fax) > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Actually - the shorter length maybe more correct - the speed of the wave (the 3 x 10^8) will be lower in a wire than in free air - which looks to be the figure used here. This means we end up with a shorter wavelength in a wire. <Quote>A radio wave in free space travels with the speed of light. When a wave travels on a transmission line, it travels slower, travelling through a dielectric/insulation. The speed at which it travels on a line compared to the free-space velocity is known as the "velocity factor". Typical figures are: Twin line 0.82, Coaxial cable 0.66, (free space 1.0). </Quote> http://www.amateur.radio.org.nz/nzart/examinat/amateur%20radio%20study%20guide/Course%20Files/Transmission%20Lines/STUDY%20NOTES%20-%20TRANSMISSION%20LINES.htm Also http://www.guerrilla.net/reference/antennas/2ghz_collinear_omni/ Using these figures we would get a 1/4 wavelength of ... 3x10^8 / 434x10^6 ------------------------- x 0.85 (approx) = 14.6 cm 4 >>> dpharrisSTOPspamspam_OUTTELUS.NET 05/14/02 01:33PM >>> Hi- Except you have 434 MHz modules, so you want: 3x10^8/434x10^6 = 0.69, so you want a 0.69/4 = 0.173 meter = 17.3 cm 1/4 wave whip. I think it needs to be straight. Hey, my 12 cm piece of wire seems to work fine, gues I should extend it. David Gary Neal wrote: -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Er. The quote refers to a transmission line - not an antennae. The correct length for an antennae is very close to the calculated free air value -but may be changed by loading coils, "top hats" and matching networks etc. If you use a transmission line e.g. coaxial cable as part of the matching network then you do need to take its velocity factor into account for this . This velocity factor is a result of the capacitive and inductive properties of the materials (pretty much entirely the diaelectric coefficient of the insulator) in the transmission line. Solid polythene gives a factor of about 0,67, expanded polythene a ration of up to about 0.84. Since an antennae is insulated by air, the velocity factor is close to 1.00. Richard P Actually - the shorter length maybe more correct - the speed of the wave (the 3 x 10^8) will be lower in a wire than in free air - which looks to be the figure used here. This means we end up with a shorter wavelength in a wire. <Quote>A radio wave in free space travels with the speed of light. When a wave travels on a transmission line, it travels slower, travelling through a dielectric/insulation. The speed at which it travels on a line compared to the free-space velocity is known as the "velocity factor". Typical figures are: Twin line 0.82, Coaxial cable 0.66, (free space 1.0). </Quote> http://www.amateur.radio.org.nz/nzart/examinat/amateur%20radio%20study%20guide/Course%20Files/Transmission%20Lines/STUDY%20NOTES%20-%20TRANSMISSION%20LINES.htm Also http://www.guerrilla.net/reference/antennas/2ghz_collinear_omni/ Using these figures we would get a 1/4 wavelength of ... 3x10^8 / 434x10^6 ------------------------- x 0.85 (approx) = 14.6 cm 4 >>> spamBeGonedpharrisSTOPspamEraseMETELUS.NET 05/14/02 01:33PM >>> Hi- Except you have 434 MHz modules, so you want: 3x10^8/434x10^6 = 0.69, so you want a 0.69/4 = 0.173 meter = 17.3 cm 1/4 wave whip. I think it needs to be straight. Hey, my 12 cm piece of wire seems to work fine, gues I should extend it. David Gary Neal wrote: -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Tue, 14 May 2002, Michael Luvara wrote: >As for antenna orientation, design, they are all good for different >things. Take a look at the aarl handbook as suggested by another list >member. The linx technology app note is good too for starters. Coils, >loops, etc run into certain constraints, like matching, etc. Most of the >time these layouts are used for space reasons, and can give lesser >results than a simple monopole. Why ? I thought the maximum possible gain of any antenna is related to its size vs. lambda. when viewed from the corresponding station. A simple monopole needs more careful matching and tuning than a dipole, and an eggbeater or discone antenna will probably outclass these two in all respects for the same lambda-related size, for example because it will leave no nulls in the horizontal or vertical plane. A simple lambda/4 whip has only one advantage: simplicity. A vertical 5/4 lambda will outclass it and give significantly more horizontal gain (and still require base tuning but less exact). For the 'lot' of matching amateurs can achieve at 433 and 900MHz a lambda/4 whip probably costs them 6dB in transmitted power (30% less possible range). This is just my limited experience. A oriented dipole Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Tue, 14 May 2002, Jim wrote: > "A simple monopole needs more careful matching > and tuning than a dipole" > >Practical experience in the real world will not >bear this out ... ever seen or used the classical >Motorola 19" whip on 2 Meters? No matching network, >mates up directly to RG-58 50 Ohm coaxial cable and >deleivers reasonable preformance for the simplicity >and size ... We are talking UHF and microwave here, low power, no voltage or power margin on the Tx, very poor noise figure on Rx (relative to what is possible), high noise background from FCC compliant (pun intended) nearby office computing equipment. Matching is everything. Tuning improves the noise margin on Rx and the useful in-band power (a little) on Tx. I don't have to tell you this. A legal 433MHz 1mW transmitter at 5V had better be matched *perfectly* to a *tuned* whip to be heard at 30 feet by a similarly prepared receiver. This is NOT the case in 99% of the cases (see millions of usenet postings - also on this list - from people who are disappointed by the range obtained), because the ground plane/shield/box whatever is not appropriate or because of nearby wires and metal objects, even if the layout, and antenna are perfect (you wish). Remember that this is not twinax in the lab or on some high end navy ship stuff or the best dreamland manufacturer figures obtained in an anechoic chamber and rounded up or down, as appropriate. > "A vertical 5/4 lambda will outclass it" > >You *might* be alluding to a "5/8 wavelength antenna" - and >you would be closer to corect ... Yes, that's right. Whew, I'm posting after midnight again ... > "a lambda/4 whip probably costs them 6dB in transmitted power" > >Again, practical experience will not quite bear this out ... This one I HAVE to insist on. Believe me, real life sucks, engineering wise, 99.999% of the time. I know because I make my living out of engineer's mistakes ;-) ;-). They are sort of, paying my salary, you see ? I'll stop now. I state based on my experience that by adding a tiny load coil (1 turn 4mm dia) and/or a 0.8pF-6pF trimmer at a whip at both Tx and Rx you can up the range by at most 30% in many cases (at 433MHz). Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

"We are talking UHF and microwave here" Then we will consider the 6" Motorola quarter-wave UHF antenna built in great quantity in this country ... a very simple antenna again containing no matching network per se and interfacing quite well to 50 coaxial cable ... I have also seen extremely simple designs at 5 GHz of the "monopole" variety - intended as an MLS receive antenna. As to contentions of extremely 'tight' link budgets owing to low power xmitters and high noise figure receivers - these factors do indeed serve to limit range ... but the fades and 'nulls' due to destructive multipath do FAR more to limit reliable range that the ever-so-cited and glorified "link budget" - as we indeed see in the real world ... Some of the 'bad' experiences with RF are due to other factors usually *not* considered - such as CPU clock noise, in-adequate grounding/counter-poise A/K/A "ground plane" for the classical monopole. One more thing that should always be remembered - *anything* used (and usable) at 10 MHz, 150 MHz or 450 MHz can be *scaled* for use at OTHER desired frequencies. That is a just fact of nature ... As most people simply lack the background, the insight required for troubleshooting RF problems *and* most don't posses the requisite test equipment or access or ever spent time on an antenna test range - "things RF" tend to remain obscure and make the job of bringing up and RF-based data system just that much more difficult ... Oh yeah, one more thing. It's ALL been done before. See the IRE (now IEEE) series dating back to the twenties ... Jim {Original Message removed}

Hi Gary, I see you have got lots of good replies so far. I'm a bit in the dark when it comes to real antenna design but for a recent design I had to use some 433MHz receiver modules and this is what I came up with. First prototype used a 173mm (1/4 wavelngth) piece of wire which worked fine. The transmitter is a 2 button keyfob remote. In fact, for the less than 10m distance I required the receiver worked well with just about any length of wire! Following the above tests I decided that the receiver wasn't going to be real fussy about the antenna for these distances, so I toyed with the idea of integrating the antenna into the PCB design. I got some really good info from http://www.rfm.com/ on antenna basics. For such a simple design the most helpful info for a PCB whip antenna I found was that the length of the whip may be 10 to 20% shorter than calculation, depending on the dielectric and the thickness of the board. They then go on to say that in most cases, 15% shorter is close enough. To cut a long story (antenna) short, I took the 173mm calculation and subtracted 15% and after a little brain (claculator) effort came up with 147mm. When it came to laying out the antenna on the board I used a 0.050" track on the bottom layer and kept it as far away as possible from everything else. I had to bend it around one corner of the board to fit it in, (all the RF designers cringe), so used as large a radius as possible. The antenna track unfortunately had to switch layers very close to the receiver module (cringe again) so I used 3 vias in a row to do this, hoping to minimise the nasty effects this most likely adds. So how did it work? Pretty good I think. I get excellent if not perfect reliability inside the 10m radius I need with any orientation of receiver/transmitter, still good within 15-20m through house walls etc, and can get something like 100m line of sight. Sorry this approach is not a good example of accurate calculation of measure of performance but hope it gives you some ideas to try. On 14 May 2002 at 11:57, Gary Neal wrote: {Quote hidden}> Guys, > > Recent discussion has peaked my interest especially since the > relatively cheap Laipac modules were introduced. I'm looking at using > the TLP434 modules outside in an open field. I'd like to get the most > range that I can. At least 150' but would be nice to get to ~600'. > Anyway, I have no experience with RF, specifically the > antenna. Can someone shed some light on this? How do you know how > long a wire to use? Do you just use a piece of wire? What gauge? > Can it still have the insulation on it? What is "loop", "whip" style > that I see listed on the Laipac page? Is the antenna different for > the transmitter and receiver? > As you can see, I'm a novice at this antenna stuff. I don't > really want a whole bunch of analytical antenna design mumbo jumbo. > Be nice if someone would say something like "Ya, just connect a piece > of 24AWG wire to the antenna that's about 3" long and that'll give you > pretty good reception". Something like that. > > Thanks, > > Gary > -- Brent Brown, Electronic Design Solutions 16 English Street, Hamilton, New Zealand Ph/fax: +64 7 849 0069 Mobile/txt: 025 334 069 eMail: KILLspambrent.brownspamBeGoneclear.net.nz -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Here's some informational links for all. When referring to matching, I was talking about the impedance between the antenna and the source it is connected to. Many antennas have baluns which go from a balanced to unbalanced medium. Reducing VSWR (Voltage Standing Wave Ratio) in antennas is very important for optimization. Directivity is a big choice for many antennas. As you narrow the antenna's beamwidth, you concentrate the power in one area therefore increasing effectivity and making a need to line up a transmit and receive antenna up together so that they can communicate easily. My experience with monopole antennas is that when you coil them, range is lost. http://www.marcspages.co.uk/tech/antgain.htm http://www.marcspages.co.uk/tech/antchose.htm If you are an arrl member: http://www.arrl.org/tis/info/antgain.html http://whatis.techtarget.com/definition/0,,sid9_gci214149,00.html On the 6dB loss in power (Watts I am assuming), only 30% loss in distance is amazing to me. I would assume more. I could be wrong though on the assumptions and have to check this in theory with the poynting theorem or friis transmission formula. It all depends on the gain of the antenna relative to an isotrop. Generally speaking, for power, 10log(X)=-6dB => X ~=.2513 => 75% loss in power. If in voltage, 20log(X)=-6dB => x = 50% loss in voltage. Michael > [Original Message] > From: Peter L. Peres <EraseMEplpEraseMEACTCOM.CO.IL> > To: <@spam@PICLIST@spam@spam_OUTMITVMA.MIT.EDU> > Date: 5/14/02 1:41:46 PM {Quote hidden}> Subject: Re: [EE]: RF modules > > On Tue, 14 May 2002, Michael Luvara wrote: > > >As for antenna orientation, design, they are all good for different > >things. Take a look at the aarl handbook as suggested by another list > >member. The linx technology app note is good too for starters. Coils, > >loops, etc run into certain constraints, like matching, etc. Most of the > >time these layouts are used for space reasons, and can give lesser > >results than a simple monopole. > > Why ? I thought the maximum possible gain of any antenna is related to its > size vs. lambda. when viewed from the corresponding station. A simple > monopole needs more careful matching and tuning than a dipole, and an > eggbeater or discone antenna will probably outclass these two in all > respects for the same lambda-related size, for example because it will > leave no nulls in the horizontal or vertical plane. > > A simple lambda/4 whip has only one advantage: simplicity. A vertical 5/4 > lambda will outclass it and give significantly more horizontal gain (and > still require base tuning but less exact). > > For the 'lot' of matching amateurs can achieve at 433 and 900MHz a > lambda/4 whip probably costs them 6dB in transmitted power (30% > less possible range). This is just my limited experience. > > A oriented dipole > > Peter > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> So you could take that 8.25cm wire and wrap it into a coil and it would be > just about as effective as leaving it straight? No, this is not true. Coiling up an antenna will have a significant effect on the resonant frequency and impedance of the antenna. The same goes for having any conductive objects in the near field vicinity of the antenna, especially if they resonate close to the operating frequency of the antenna. To use a 1/4 wave antenna efficiently, it needs a ground plane. A long wire (>1 wavelength) does not need this, but will need some type of impedance matching to your rf equipment, it will also be directional. > Can I use just normal stranded ~24AWG hookup wire for the antenna? Does > the insulation around the wire matter? Yes you can leave it on. The insulation really makes very little difference in your case. Strictly speaking, the insulation does have an effect on the velocity factor of the the wire used as the radiator. It does not resist the rf from being able to leave the wire. Suffice it to say that much experimentation is in order here. You will find things that work fine for you (regardless of what the "experts" say), and you will most assuredly find that your real-world measurements will never exactly match your calculated expectations. Antenna theory and design is black magic. ;-) All that other stuff aside, for your application (low power/short range) a piece of 24 ga. insulated wire approximately 1/4 wavelength long will, in all probability, work just fine. ;-) > Thanks, > > Gary > > At 09:25 AM 5/14/2002 -0700, you wrote: > >Antennas are a whole subject in itself. They come in all sizes, shapes, and > >colors. Simply put, a monopole is a simple antenna which is a single piece > >of wire, usually called a whip in most forms. Antennas should be tailored to > >the frequency being used. Moreover, they need to be tuned to listen in for a > >specfic frequency's wavelength or a function of it. Depending on the > >frequency and type of usage, there are different antennas for different > >applications. Higher frequencies tend to be more directional as you go up in > >freq which creates the need for antennas that can transmit or listen in all {Quote hidden}> >or specified directions. > > > >A 1/4 wave antenna works fine for most applications. Use this relation to > >figure this out required length: C= lamda x V, where c= 3 x 10^8, V = > >frequency, and lambda = wavelength. > > > >For example, a 900MHz device would need: > > > >3 x 10^8 / 900 x 10^6 = .333 meter wavelength. Dividing this by 4, only a > >8.25 cm long antenna is needed. This can be a loop, coil, etc. > > > >Linx technologies has a good primer on antennas. > >www.linxtechnologies.com/ldocs/pdfs/AN00500.pdf > > > >Also, they have an antenna site. > >http://www.antennafactor.com/adocs/f_prod.html > > > >Hope this helps, > >Michael > > > > > [Original Message] > > > From: Gary Neal <.....gln103spam_OUTPSU.EDU> > > > To: <TakeThisOuTPICLIST.....TakeThisOuTMITVMA.MIT.EDU> > > > Date: 5/14/02 8:57:12 AM > > > Subject: Re: [EE]: RF modules > > > > > > Guys, > > > > > > Recent discussion has peaked my interest especially since the > > > relatively cheap Laipac modules were introduced. I'm looking at using the > > > TLP434 modules outside in an open field. I'd like to get the most range > > > that I can. At least 150' but would be nice to get to ~600'. > > > Anyway, I have no experience with RF, specifically the > > > antenna. Can someone shed some light on this? How do you know how long a > > > wire to use? Do you just use a piece of wire? What gauge? Can it still > > > have the insulation on it? What is "loop", "whip" style that I see listed > > > on the Laipac page? Is the antenna different for the transmitter and > >receiver? > > > As you can see, I'm a novice at this antenna stuff. I don't > > > really want a whole bunch of analytical antenna design mumbo jumbo. Be > > > nice if someone would say something like "Ya, just connect a piece of > >24AWG > > > wire to the antenna that's about 3" long and that'll give you pretty good {Quote hidden}> > > reception". Something like that. > > > > > > Thanks, > > > > > > Gary > > Gary Neal > Research Assistant - Drivetrain Technology Center > Applied Research Laboratory - Penn State University > PO Box 30 > Research Building West > North Atherton Street > State College, PA 16801 > 814-863-5468 (phone) > 814-863-6185 (fax) > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email TakeThisOuTlistservKILLspamspammitvma.mit.edu with SET PICList DIGEST in the body

> Er. > The quote refers to a transmission line - not an antennae. > The correct length for an antennae is very close to the calculated free > air value -but may be changed by loading coils, "top hats" and matching > networks etc. > If you use a transmission line e.g. coaxial cable as part of the matching > network then you do need to take its velocity factor into account for this > . > This velocity factor is a result of the capacitive and inductive properties > of the materials (pretty much entirely the diaelectric coefficient of the > insulator) in the transmission line. Solid polythene gives a factor of > about 0,67, expanded polythene a ration of up to about 0.84. Since an > antennae is insulated by air, the velocity factor is close to 1.00. > > Richard P Hmm, I respectfully disagree. The antenna itself is a continuation of the transmission line. While it may not have as low a velocity factor as the coax feeding it, it still has inductance (and consequently reactance) and will manifest that as a velocity factor <1. I think the fact that top-hats and coils have the effect that they do proves this out. michael brown (really sticking my neck out now) -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservRemoveMEmitvma.mit.edu with SET PICList DIGEST in the body

michael brown schrieb: {Quote hidden}> > > Er. > > The quote refers to a transmission line - not an antennae. > > The correct length for an antennae is very close to the calculated free > > air value -but may be changed by loading coils, "top hats" and matching > > networks etc. > > If you use a transmission line e.g. coaxial cable as part of the matching > > network then you do need to take its velocity factor into account for this > > . > > This velocity factor is a result of the capacitive and inductive > properties > > of the materials (pretty much entirely the diaelectric coefficient of the > > insulator) in the transmission line. Solid polythene gives a factor of > > about 0,67, expanded polythene a ration of up to about 0.84. Since an > > antennae is insulated by air, the velocity factor is close to 1.00. > > > > Richard P > > Hmm, I respectfully disagree. The antenna itself is a continuation of the > transmission line. While it may not have as low a velocity factor as the > coax feeding it, it still has inductance (and consequently reactance) and > will manifest that as a velocity factor <1. At this point I have to disagree! In the vacuum a conductor will still have L and C components per bit of length, but the propagation velocity will be just below C. The L and C values determine the RF impedance, not the propagation velocity. Any dielectric around it which is not a vacuum (or air, if one doesn't look too closely), the diameter of the conductor will mainly influence the Zw, not the Vp. Greets Jochen Feldhaar DH6FAZ (my 0.02 EUR...) I think the fact that top-hats > and coils have the effect that they do proves this out. > > michael brown (really sticking my neck out now) > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email RemoveMElistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistserv@spam@spam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Just to clarify . The group velocity in a transmission line is equal to sqrt(permeability x permittivity) of the surrounding medium. The velocity ratio is therefore the sqrt(rel. permittivity x rel. permeability) [- Sorry re spelling ?-] Since the rel permeability (magnetic component) is normally very close to 1 (magnetic materials are also somewhat lossy), the velocity ratio is almost entirly due to the permittivity (capacative effect) of the surrounding medium. In transmission lines this is the insulator and the velocity factor is normally pretty much the same as sqrt(er) which also equals sqrt(1/dielectric constant) In an antennae, the radiation is produced by the interaction of the magnetic field (current in the conductor) and the electic field (voltage to ground). Since the surrounding medium is air, which has an rel permittivitty and rel. permeability close to 1, the velocity ratio is also close to 1. If a "top hat" is added to the antennae, the capacitance is increased (due to the increase in area) and the current in the conductor increases, at the expense of the peak voltage. This also reduces the resonant frequency of the antennae and allows a shorter annennae to be used at lower frequencies. Similarly, a loading coil at the base of an antennae will increase the inductance and similarly decrease the resonant frequency. Now, if a matching network is applied to the feed, this may also add capacitance and/or inductance to the circuit, also reducing the resonant frequency and resulting in a slightly smaller overall structure - possibly the 15% or so you mention in an earlier email. Also , a 1/4 wave antenae on an "infinite" ground plane has an impedance of ~ 37.5 ohms but on a more normal ground plane, in practice, the impedance is slightly higher. Because it is not infinite however, the L & C are slightly unbalanced resulting in a reactive component. Therefore a magnetude match is the best acheivable (without additional components) and this requires the length of the antennae to be reduced slightly. At least , that is how I understand it. I don't even want to consider thinking about how this impacts radiation patterns and gains etc. Richard P > Er. > The quote refers to a transmission line - not an antennae. > The correct length for an antennae is very close to the calculated free > air value -but may be changed by loading coils, "top hats" and matching > networks etc. > If you use a transmission line e.g. coaxial cable as part of the matching > network then you do need to take its velocity factor into account for this > . > This velocity factor is a result of the capacitive and inductive properties > of the materials (pretty much entirely the diaelectric coefficient of the > insulator) in the transmission line. Solid polythene gives a factor of > about 0,67, expanded polythene a ration of up to about 0.84. Since an > antennae is insulated by air, the velocity factor is close to 1.00. > > Richard P Hmm, I respectfully disagree. The antenna itself is a continuation of the transmission line. While it may not have as low a velocity factor as the coax feeding it, it still has inductance (and consequently reactance) and will manifest that as a velocity factor <1. I think the fact that top-hats and coils have the effect that they do proves this out. michael brown (really sticking my neck out now) -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservEraseMEmitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

> Just to clarify . <snipped very good explanation of velocity factor> > In an antennae, the radiation is produced by the interaction of the > magnetic field (current in the conductor) and the electic field (voltage to > ground). Since the surrounding medium is > air, which has an rel permittivitty and rel. permeability close to 1, the > velocity ratio is also close to 1. I humbly submit that you *must* be right about this. I was under the impression that the inductance of the antenna radiator itself would result in a decreased velocity factor. Obviously, I was quite mistaken about this. ;-) > If a "top hat" is added to the antennae, the capacitance is increased (due > to the increase in area) and the current in the conductor increases, at the > expense of the peak voltage. This also reduces the resonant frequency of > the antennae and allows a shorter annennae to be used at lower frequencies. Whilst this is true, I think that the primary reason "top hats" are used is to lower Q and increase usable bandwidth (by reducing SWR). > Similarly, a loading coil at the base of an antennae will increase the > inductance and similarly decrease the resonant frequency. This is most definitely true. > Now, if a matching network is applied to the feed, this may also add > capacitance and/or inductance to the circuit, also reducing the resonant > frequency and resulting in a slightly > smaller overall structure - possibly the 15% or so you mention in an > earlier email. Capacitance would serve to electrically shorten the antenna, resulting in an apparant increase of the resonant frequency. Inductance, as you stated, reduces the resonant frequency. > Also , a 1/4 wave antenae on an "infinite" ground plane has an impedance of > ~ 37.5 ohms but on a more normal ground plane, in practice, the impedance > is slightly higher. Because it is not infinite however, the L & C are > slightly unbalanced resulting in a reactive component. Therefore a > magnetude match is the best acheivable (without additional components) and > this requires the length of the antennae to be reduced slightly. Shortening it would add capacitive reactance (I do believe) resulting in an "apparant" feed point impedance (Z + Xc) that is closer to 50 ohms. This is one of those antenna areas where something appears to be a benifit (lower SWR), but in all reality it is detriment (anntenna is not being used at resonant frequency (by resonant frequency I mean Xc = Xl = 0) This would result in lobe distortion in the radiation pattern, heat generation in the antenna, and other inefficiencies, I believe. > At least , that is how I understand it. Sounds like you have a pretty good handle on things. ;-) The one point I would like to make, for the benefit of others reading this, is that antenna matching circuits (tuners, as most call them) do not make an antenna work "better", they just make the transmitter happy. An antenna works best when operated at it's resonant frequency, regardless of the feed point impedance that results. Having made a "few" antennas (for transmitting as well as recieving), it has been my experience that as frequency goes up, the bigger the gap gets between textbook formulas and real world working values. HF antennas are easy to work with, VHF gets to be a pain very quickly. ;-) > I don't even want to consider thinking about how this impacts radiation > patterns and gains etc. Oops, I kinda brought that up already. ;-) {Quote hidden}> > Richard P > > > > > Er. > > The quote refers to a transmission line - not an antennae. > > The correct length for an antennae is very close to the calculated free > > air value -but may be changed by loading coils, "top hats" and matching > > networks etc. > > If you use a transmission line e.g. coaxial cable as part of the matching > > network then you do need to take its velocity factor into account for > this > > . > > This velocity factor is a result of the capacitive and inductive > properties > > of the materials (pretty much entirely the diaelectric coefficient of the > > insulator) in the transmission line. Solid polythene gives a factor of > > about 0,67, expanded polythene a ration of up to about 0.84. Since an > > antennae is insulated by air, the velocity factor is close to 1.00. > > > > Richard P > > Hmm, I respectfully disagree. The antenna itself is a continuation of the > transmission line. While it may not have as low a velocity factor as the > coax feeding it, it still has inductance (and consequently reactance) and > will manifest that as a velocity factor <1. I think the fact that top-hats {Quote hidden}> and coils have the effect that they do proves this out. > > michael brown (really sticking my neck out now) > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email @spam@listservspam_OUT.....mitvma.mit.edu with SET PICList DIGEST in the body > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email spamBeGonelistservEraseMEmitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspamBeGonemitvma.mit.edu

{Quote hidden}> >> > > Success with printed circuit antenna over 10m and up to 20m > >> > > >> > What modules did you use and were they standard legal power (1mW > >> > 433MHz) if I may ask ? Was it a superregenerative receiver ? (I > >> > think not). > >> > >> Peter, > >> > >> Have a look at http://www.automicro.com.tw/. The receivers are the > >> RX4303, the transmitters are TX3314S. > > > >Further to the above, I have been in the touch with the manufacturers > >of these devices and they say the TX3314S has about 5mW RF output > >power. Here in NZ it appears we are now allowed 25mW EIRP on this > >band, (used to be 1mW), not sure about other countries. > > Aha! That explains a lot. 1mW->5mW is quite a change (4+ times power = > 2*range -> from max 30 meters to 60 meters in the same conditions). > > This NZ seems to be a mythical country ;-) They are allowed four times > more than others <g>. What else comes in fourfold portions in NZ ? (I > hope not taxes <g>) > Yes of course it's a mythical place, but don't tell everyone...we like to keep it a secret. Have you seen Lord of the Rings? It's exactly like that here. And Start Wars Episode II - who else would you clone if you wanted to make the best army in the universe? Back on topic... the 433MHz band here apparently used to be restricted to 10uW, then 1mW, now 25mW. That's a 2500 fold increase. From looking around I think in Europe you can have 10mW. I'll stick with 5mW now just in case I ever have to export to Europe, though I wouldn't be really excited about all the compliance stuff. -- Brent Brown, Electronic Design Solutions 16 English Street, Hamilton, New Zealand Ph/fax: +64 7 849 0069 Mobile/txt: 025 334 069 eMail: RemoveMEbrent.brownEraseMEKILLspamclear.net.nz -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspam_OUTRemoveMEmitvma.mit.edu with SET PICList DIGEST in the body