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'[EE]: RF modules'
2002\05\11@180407 by G Brigley

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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

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2002\05\13@005134 by Ann & David Scott

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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....

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2002\05\13@032917 by David P. Harris

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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:

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2002\05\13@123711 by jpalvarez

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You can check chip modules at:

http://www.rentron.com

JP

-----Original Message-----
From: pic microcontroller discussion list
[.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU]On Behalf Of Ann & David Scott
Sent: Sunday, May 12, 2002 10:40 PM
To: PICLISTspamKILLspamMITVMA.MIT.EDU
Subject: Re: [EE]: RF modules


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....

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2002\05\13@132404 by G Brigley

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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}

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2002\05\13@152713 by David P. Harris

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You are aware of John Dammeyer's system?
Wireless CAN with the CANRF module.
www.autoartisans.com/documents/canrf_prod_announcement.pdf
Automation Artisans Inc.
Ph. 1 250 544 4950

David

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.

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2002\05\13@161833 by Kevin Olalde

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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:
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2002\05\13@163152 by John Dammeyer

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Hi Kevin,

Tell us how you went about doing collision detection.

Thanks.

John Dammeyer



Wireless CAN with the CANRF module.
www.autoartisans.com/documents/canrf_prod_announcement.pdf
Automation Artisans Inc.
Ph. 1 250 544 4950


> {Original Message removed}

2002\05\13@172113 by Kevin Olalde

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Believe me, I'm all too easy a target to drag though the mud.  So that said, I'm
all for someone helping me to understand and help correct my mistakes (just a
hobby, and I've got zero background in this).

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.

Ready for semantic and technique corrections.

Thanks,
Kevin


John Dammeyer wrote:
>
> Hi Kevin,
>
> Tell us how you went about doing collision detection.
>
> Thanks.
>
> John Dammeyer
>

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2002\05\13@180040 by Russell McMahon

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> > 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

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2002\05\13@190650 by John Dammeyer

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Hi Kevin,

Sounds simple enough.  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.

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.

I take it then that you send an acknowledge back with for every message?

And, out of curiosity,  how do you determine if someone is transmitting?

Cheers,

John Dammeyer

> {Original Message removed}

2002\05\13@203314 by John Dammeyer

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Yes,  I meant it to go to the list.

John



Wireless CAN with the CANRF module.
www.autoartisans.com/documents/canrf_prod_announcement.pdf
Automation Artisans Inc.
Ph. 1 250 544 4950


> {Original Message removed}

2002\05\13@203720 by Kevin Olalde

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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:
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2002\05\13@211648 by Kevin Olalde

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> 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

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2002\05\13@222953 by G Brigley

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On Mon, 13 May 2002, Kevin Olalde wrote:
> Now if I only could find some RF modules that were cheap AND legal for this
> application...

I think I'm going to go with the Laipac RLP916A and TLP916A for my
application.  Each set comes in at about US $20.  When I started
this
project, I thought I'd be spending 5 times that.

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2002\05\13@231752 by John Dammeyer

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>
> > 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}

So the signal is ASK or FM?

John

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2002\05\13@234650 by Kevin Olalde

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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}

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

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2002\05\14@005806 by John Dammeyer

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>
> 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}

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


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2002\05\14@070424 by Olin Lathrop

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> 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.

Does your protocol guarantee that there is always a 1 bit in any successive
3 bits?


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2002\05\14@074356 by Russell McMahon

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> 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

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2002\05\14@080724 by Kevin Olalde

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I think so, 3 bits was a shoot from the hip number.  I'm manchester encoding so
I think I'll have at least one '1' bit per three, and my preamble, sync byte and
stop byte are all 'balance'.  Hmmm, maybe I should sample for a couple more
bits?  Three is the bare minumum.

Thanks,
Kevin

Olin Lathrop wrote:
>
> > 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.
>
> Does your protocol guarantee that there is always a 1 bit in any successive
> 3 bits?

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2002\05\14@081353 by Kevin Olalde

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> > Can you shed some light?
>
<snip>
>
> Hope that helps a bit.

Quite a bit, thanks,
Kevin

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2002\05\14@113100 by Michael Luvara

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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 <.....gobrigleKILLspamspam.....ENGMAIL.UWATERLOO.CA>
> To: <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
> Date: 5/13/02 10:21:52 AM
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2002\05\14@115922 by Gary Neal

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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}

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)

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2002\05\14@122734 by TimS800

flavicon
face
thank you
----- Original Message -----
From: "G Brigley" <gobriglespamspam_OUTENGMAIL.UWATERLOO.CA>
To: <@spam@PICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Monday, May 13, 2002 7:26 PM
Subject: Re: [EE]: RF modules


> On Mon, 13 May 2002, Kevin Olalde wrote:
> > Now if I only could find some RF modules that were cheap AND legal for
this
{Quote hidden}

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2002\05\14@122746 by Michael Luvara

picon face
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 <KILLspamgln103KILLspamspamPSU.EDU>
> To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
> Date: 5/14/02 8:57:12 AM
{Quote hidden}

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

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2002\05\14@123518 by Gary Neal
picon face
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}

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)

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2002\05\14@131124 by Eoin Ross

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face
The ARRL handbook (you may be able to find one at your local library - or whole books on the subject) has info on a number of different styles of aerial/antenna.

They normally have some plain language in them and formula for working out the length. A 1/4 wave whip is usually the easiest to figure in size and mounting  - see another post for the formula.

Eoin

>>> RemoveMEgln103spamTakeThisOuTPSU.EDU 05/14/02 11:57AM >>>
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.  <snip>
        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

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2002\05\14@132045 by G Brigley

flavicon
face
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}

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2002\05\14@133015 by Michael Luvara

picon face
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 <RemoveMEgobrigleEraseMEspamEraseMEengmail.uwaterloo.ca>
> To: Michael Luvara <RemoveMEmluvaraspam_OUTspamKILLspamearthlink.net>
> Cc: <RemoveMEPICLISTTakeThisOuTspamspamMITVMA.MIT.EDU>
> Date: 5/14/02 10:18:22 AM
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2002\05\14@141250 by David P. Harris

picon face
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:

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2002\05\14@151550 by Eoin Ross

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face
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


>>> dpharrisSTOPspamspamspam_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:

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2002\05\14@161718 by hard Prosser

flavicon
face
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


>>> spamBeGonedpharrisSTOPspamspamEraseMETELUS.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:

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2002\05\14@173115 by Peter L. Peres

picon face
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

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2002\05\14@173134 by Peter L. Peres

picon face
On Tue, 14 May 2002, G Brigley wrote:

>What is the definition of a telemetry system?  I've seen that term a lot
>while I've been shopping for modules.

A system that allows remote measurement of something (telemetry means
exactly that, in Greek, spelled 'telemetria' I think).

Peter

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2002\05\14@175228 by Jim

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  "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 ...

  "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 ...

 "a lambda/4 whip probably costs them 6dB in transmitted power"

Again, practical experience will not quite bear this out ...

Jim


{Original Message removed}

2002\05\14@182027 by Peter L. Peres

picon face
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

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2002\05\14@184107 by Jim

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face
  "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}

2002\05\14@185154 by Jim

flavicon
face
I nearly over-looked some work I did on a
project just this last year - using 1/4 wave
Motorola 800 MHz 3" monopoles ... if anybody
needs a rugged outdoor antenna for a project
that presents a *good* match across the cellular
band (other freq ranges *are* available BTW) -

- then the series by **Maxrad** looks REALLY
REALLY good (swept them with my HP 8410B VNA)
... and available at US$3.something each ...


Jim


{Original Message removed}

2002\05\14@192521 by Brent Brown

picon face
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}

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Mobile/txt: 025 334 069
eMail:  KILLspambrent.brownspamBeGonespamclear.net.nz

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2002\05\15@015728 by mluvara

picon face
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 <EraseMEplpspamEraseMEACTCOM.CO.IL>
> To: <@spam@PICLIST@spam@spamspam_OUTMITVMA.MIT.EDU>
> Date: 5/14/02 1:41:46 PM
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2002\05\15@070201 by michael brown

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face
> 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}

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}

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2002\05\15@071403 by michael brown

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face
> 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)

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2002\05\15@072713 by Jochen Feldhaar

flavicon
face
michael brown schrieb:
{Quote hidden}

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)
>
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2002\05\15@135631 by Peter L. Peres

picon face
> 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

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2002\05\15@175516 by hard Prosser

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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)

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2002\05\15@194317 by Brent Brown

picon face
> > 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.
--
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Mobile/txt: 025 334 069
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2002\05\16@071941 by michael brown

flavicon
face
> 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}

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}

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2002\05\16@075320 by innoelec

flavicon
face
Hi all
I have been using similar models from same company for over two years now.
(RX3302)
they are really good and cheap .In clear area some times the distance reach
more than 120 meter while inside city ,homes is nearly 50-70 meter
most of my projects using key chains transmitters (from the same company )
and a receiver modules and I use PIC to decode , learn and save .
And now the company make new modules using FM modulation (I did not tested
yet but I think the samples would arrived in two weeks )
that would able the two parties to communicate till 350 meter

Nouman Al-Mounajed
RemoveMEowner@spam@spamspamBeGoneinnoelec.com


{Original Message removed}

2002\05\16@081328 by Olin Lathrop

face picon face
> 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.  The geometry matters also.

> Can I use just normal stranded ~24AWG hookup wire for the antenna?

Yes.

> Does the insulation around the wire matter?

Usually not.  Some insulation might start doing strange things at high
frequencies, like absobing energy, but this is usually not an issue.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\05\16@085242 by Russell McMahon

face
flavicon
face
> 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.  ;-)

Just to show that SOME people dwell in that world of arcane magic with some
degree of competence and confidence, here is a reference to a mind boggling
(mine anyway) and superb free internet book

The Microwave antenna Book -

       http://www.w1ghz.cx/antbook/contents.htm

by W1GHZ (the name tells you something :-) )

Free to download for non-commercial use. $US73 for commercial use.

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2002\05\16@091950 by Thomas C. Sefranek

face picon face
On 17 May 2002 at 0:50, Russell McMahon wrote:

> The Microwave antenna Book -
>
>         http://www.w1ghz.cx/antbook/contents.htm
>
> by W1GHZ (the name tells you something :-) )

Actually Paul Wade does some "Evangelizing" [Paul] of microwave bands,
and also I have known him to "Wade" right in to the pool of collected "wisdom"
of amateur radio... to drain the swamp.

What does it say when "we" use the callsign as someone's name...
Us OLD Ham radio operators know more people by their callsign than by their given
name.

{Quote hidden}

 |  __O    Thomas C. Sefranek  tcsEraseMEspam@spam@cmcorp.com
 |_-\<,_   Amateur Radio Operator: WA1RHP
 (*)/ (*)  Bicycle mobile on 145.41, 448.625 MHz

ARRL Instructor, Technical Specialist, VE Contact.
hamradio.cmcorp.com/inventory/Inventory.html
http://www.harvardrepeater.org

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2002\05\20@105905 by Brent Brown

picon face
> > > 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.
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Mobile/txt: 025 334 069
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2002\05\20@150213 by Peter L. Peres

picon face
On Mon, 20 May 2002, Brent Brown wrote:

>> > > 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>)

Peter

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2002\05\20@174909 by Brent Brown

picon face
{Quote hidden}

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.
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Mobile/txt: 025 334 069
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2002\05\20@181449 by Dale Botkin

flavicon
face
Maybe part of it is that in NZ 25mW will only get you partway across the
country, and certainly not interfere with anything on Oz.  In Europe you
could potentially cover several countries with that level of power,
especially if one of them is Luxembourg...

<grins, ducks to avoid objects thrown by our European friends...>

Dale
--
"Curiosity is the very basis of education and if you tell me that
curiosity killed the cat, I say only the cat died nobly."
         - Arnold Edinborough


On Tue, 21 May 2002, Brent Brown wrote:

> 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.

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2002\05\20@193803 by John Dammeyer

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Hi,

Remember though, from earlier on in this thread,  that 433MHz here in
North America is restricted to the amount of time you can spend on the
air and that no continuous or networking type stuff is allowed.  They
could allow 1Kw and it still wouldn't help if you wanted to do a network
with multiple nodes chatting with each other.

John Dammeyer



Wireless CAN with the CANRF module.
www.autoartisans.com/documents/canrf_prod_announcement.pdf
Automation Artisans Inc.
Ph. 1 250 544 4950


> {Original Message removed}

2002\05\21@030834 by Mircea Chiriciuc

flavicon
face
In case you will export to europe, here's a suggesstion: use 10mW RF modules
and put an atenuator between the transmiter and the antena so you can adjust
the output power accordingly.

Mircea Chiriciuc
EMCO INVEST

{Original Message removed}

2002\05\21@041417 by Alan B. Pearce

face picon face
> 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>)

Of course it is. It is not known as "Gods Own Country" for nothing. :)

Slightly larger than the UK for land area, and less human population than
Scotland :)

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2002\05\21@132530 by John Dammeyer

flavicon
face
I have a problem with that technique.  Dropping your output power with
an attenuator will also drop your receive signal.  You'd have to add a
switch of some sort and I think that brings the price way out of line.

John Dammeyer



Wireless CAN with the CANRF module.
www.autoartisans.com/documents/canrf_prod_announcement.pdf
Automation Artisans Inc.
Ph. 1 250 544 4950


> {Original Message removed}

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