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'[EE] Long range wireless thermometer problem solve'
2006\09\29@105737 by Art

picon face
Earlier this week, I wrote a message asking how to increase the range
of my Oregon Scientific wireless temperature sensing remote
transmitters that come with the BAR-888A atomic clock.

Thanks to a user here that wrote me off list...the problem is solved.

For a long range transmitter, use a wireless amp module such as the
Phillips BGY687B. It is a simple amplifier that can be used without
input and output tuning if spectral purity is not an issue. This amp
operates with milliwatt input power levels such as these low power
433 Mhz transmitters produce and can produce a 1 watt output
transmitter or more.

The device is a CATV broadband amplifier module, it's easy to use and
already has 50 ohm input and output impedances.

This is a simple fix for a significant boost in range. You will
exceed the (ISM) FCC limits for power output by doing this, so do so
at your own risk...or, get an amateur radio license and run as much
output power as you want....these devices operate in amateur radio
spectrum where amateur's have the primary spectrum allocation. So,
it's all quite legal provided the amateur service rules and
regulations are complied with.

You can also get another 10 db of effective radiated power by simply
adding a small quarter wave dipole transmitting antenna, the stock
PCB loop antennas are not good::> This also violates FCC rules unless
one has an amateur radio license.

This should give you a 1 mile range, or more...depending on the terrain.

-----------------------------------------------------------------------------


In the process of my research, I found these devices use SAW devices
to set the operating frequency. Saw devices have poor stability and
are very sensitive to temperature changes. As a result of the saw
use, the transmitted frequency can vary by 200 KHz (or more). This
means that receivers have to be very broadbanded, so they admit a lot
of noise, which reduces the transmitting range.

So, converting to quartz crystal receivers and transmitters on both
ends of the link can easily add another 15 db of sensitivity (or more).


----------------------------------------------------------------------------

For the ultimate in range, use the remote temperature unit in it's
stock configuration and buy a simplex repeater (Wireless Signal
Repeater, model RT918) sold by Oregon Scientific. This is a simple
receiver and re-transmitter that listens on 433 Mhz until it hears a
digital signal from the remote temperature transmitter. When the
signal is heard, it stores the signal, then re-transmits it (on the
same frequency) a few milliseconds later. By converting one of these
repeaters to high power as explained above, the entire repeater
assembly can be placed at the feedpoint of a hygain yagi antenna
antenna for extremely long range transmissions.

20 or 30 miles (or longer) range should be easily obtainable
depending on the terrain and how high/big the outdoor antenna is.

Enjoy::>

Art


Disclaimer:These 433 Mhz license free devices are regulated by the
FCC (in the US) and cannot be modified legally in any way unless they
are operated under an amateur radio license or a part 5 experimental
license. If you choose to modify one of these units, you must comply
with all applicable rules and regulations. This is your
responsibility, not mine.



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2006\09\29@110727 by Marc Nicholas

picon face
Glad to hear you solved it. I was going to recommend a traditional
thermometer and a telescope ;-)

-marc

On 9/29/06, Art <spam_OUTKY1KTakeThisOuTspamverizon.net> wrote:
{Quote hidden}

> -

2006\09\29@112421 by Vasile Surducan

face picon face
On 9/29/06, Art <.....KY1KKILLspamspam@spam@verizon.net> wrote:

snip
> For a long range transmitter, use a wireless amp module such as the
> Phillips BGY687B. It is a simple amplifier that can be used without
> input and output tuning if spectral purity is not an issue. This amp
> operates with milliwatt input power levels such as these low power
> 433 Mhz transmitters produce and can produce a 1 watt output
> transmitter or more.
>
snip
>
> This should give you a 1 mile range, or more...depending on the terrain.
>

A RadioShack $20 talky-walky pair is able to communicate perfect on
LOS at 8.5Km (about 5 miles) with own antennas.

greetings,
Vasile

2006\09\29@112844 by David VanHorn

picon face
>
> In the process of my research, I found these devices use SAW devices
> to set the operating frequency. Saw devices have poor stability and
> are very sensitive to temperature changes. As a result of the saw
> use, the transmitted frequency can vary by 200 KHz (or more). This
> means that receivers have to be very broadbanded, so they admit a lot
> of noise, which reduces the transmitting range.



As a matter of sheer politeness, doing this job with antenna gain makes a
LOT more sense.
It wouldn't be hard to get 20dB gain from good antennas at both ends. (+10
on each end)
While this still violates FCC regs (even with a ham licence, they have no
provision for ID), it at least remains in the spirit.
You're emitting the same energy, just concentrating it.  I have never really
understood why gain antennas are prohibited, since you sacrifice painted
area for gain.

I'll point out too, that you can do anything you like to the RECEIVER, and
stay within part 15.
Sitting the transmitter at a point between three metal walls, so that it
forms a corner reflector, is probably also sleazeable.
You didn't touch the product, you just set it RIGHT HERE.. :)

At 433, you're sitting between weak signal work, and repeater control links.

KEEP OUR SPECTRUM CLEAN!  :)

2006\09\29@113305 by David VanHorn

picon face
>
>
> As a matter of sheer politeness, doing this job with antenna gain makes a
> LOT more sense.
> It wouldn't be hard to get 20dB gain from good antennas at both ends. (+10
> on each end)
>

To put that in perspective, assuming a clear path, 6dB doubles your range,
and it dosen't much matter which end it's on.
So easily 8x the normal range, with just antennas, and no additional power
consumption.

2006\09\29@114510 by David VanHorn

picon face
>
>
> A RadioShack $20 talky-walky pair is able to communicate perfect on
> LOS at 8.5Km (about 5 miles) with own antennas.


In a vaccuum, with a tail wind  :)

2006\09\29@115856 by Art

picon face
At 11:21 AM 9/29/2006, you wrote:

> >
> > In the process of my research, I found these devices use SAW devices
> > to set the operating frequency. Saw devices have poor stability and
> > are very sensitive to temperature changes. As a result of the saw
> > use, the transmitted frequency can vary by 200 KHz (or more). This
> > means that receivers have to be very broadbanded, so they admit a lot
> > of noise, which reduces the transmitting range.
>
>
>
>As a matter of sheer politeness, doing this job with antenna gain makes a
>LOT more sense.
>It wouldn't be hard to get 20dB gain from good antennas at both ends. (+10
>on each end)
>While this still violates FCC regs (even with a ham licence, they have no
>provision for ID), it at least remains in the spirit.


Yes, you have to comply with all amateur regs, so a simple OOK PIC CW
ID generator and timer would have to be added also.


>You're emitting the same energy, just concentrating it.  I have never really
>understood why gain antennas are prohibited, since you sacrifice painted
>area for gain.
>
>I'll point out too, that you can do anything you like to the RECEIVER, and
>stay within part 15.


NO NO NO..........first of all, it's NOT part 15!

Also, the receiver and/or receiving antennas cannot be modified
either because type acceptance certification will be invalidated. So,
to stay within the ISM service guidelines, you cannot modify the
receiver or antenna either.


>Sitting the transmitter at a point between three metal walls, so that it
>forms a corner reflector, is probably also sleazeable.
>You didn't touch the product, you just set it RIGHT HERE.. :)
>
>At 433, you're sitting between weak signal work, and repeater control links.
>
>KEEP OUR SPECTRUM CLEAN!  :)

Personally, I wouldn't amplify a SAW based transmitter and I think
they should be disallowed even on low power transmitters on UHF
frequencies. However, I don't make the rules::> Quartz crystals can
be bought for as little as 28 cents each (single quan, I just bought
one from Digikey). So price is not justification for a sloppy
frequency controlling element such as a SAW.

Regards,

Art



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2006\09\29@121522 by David VanHorn

picon face
>
>
> NO NO NO..........first of all, it's NOT part 15!


Are you sure of that?
If so, how are they being sold?

Also, the receiver and/or receiving antennas cannot be modified
> either because type acceptance certification will be invalidated. So,
> to stay within the ISM service guidelines, you cannot modify the
> receiver or antenna either.


I've always seen that notice on transmitters, but NEVER on a receiver.
What about a scanner?  You can't tell me that they do testing with EVERY
antenna for part 15 cert?


> Personally, I wouldn't amplify a SAW based transmitter and I think
> they should be disallowed even on low power transmitters on UHF
> frequencies.


I agree, sloppy as hell, but apparently slightly cheaper than crystals.


> So price is not justification for a sloppy
> frequency controlling element such as a SAW.


I've been brutalized in a design meeting over $0.05 in a BOM.

2006\09\29@193906 by peter green

flavicon
face
> I have
> never really
> understood why gain antennas are prohibited, since you sacrifice painted
> area for gain.
maybe you'd think differently if your house happened to end up in someones
concentrated beam and so none of your equipment on that band worked
properly.


2006\09\29@194611 by David VanHorn

picon face
>
> maybe you'd think differently if your house happened to end up in someones
> concentrated beam and so none of your equipment on that band worked
> properly.


Possible.. but as you increase gain, you reduce beamwidth..
But I see what you mean, perhaps they were trying to keep the power at any
given point below X.

2006\09\29@211147 by Howard Winter

face
flavicon
picon face
Dave,

On Fri, 29 Sep 2006 19:46:10 -0400, David VanHorn wrote:

> > maybe you'd think differently if your house happened to end up in someones
> > concentrated beam and so none of your equipment on that band worked
> > properly.
>
>
> Possible.. but as you increase gain, you reduce beamwidth..
> But I see what you mean, perhaps they were trying to keep the power at any
> given point below X.

Yes, it's all about field strength.  When CB radio was legalised here I had a home installation (the aerial on the roof was a bit of a giveaway) and one
of my neighbours complained of interference.  I had a visit from a couple of blokes from the Interfernce Branch of the Department of Trade &
Industry.  They measured the output of my transmitter at the socket, then measured the field strength outside and reported that it was "within
expected limits", so I wasn't to blame!

Cheers,


Howard Winter
St.Albans, England


2006\09\30@030251 by Vasile Surducan

face picon face
On 9/29/06, David VanHorn <dvanhornspamKILLspammicrobrix.com> wrote:
> >
> >
> > A RadioShack $20 talky-walky pair is able to communicate perfect on
> > LOS at 8.5Km (about 5 miles) with own antennas.
>
>
> In a vaccuum, with a tail wind  :)

No, in Romania, when I've tested an 8.5Km  LOS, WIMAX FDD link on
2.45GHz and 5.6GHz. We've used 433Mhz for antena alignment.
I was deeply surprised talking with two 433Mhz talky walky models, a
smallest size $20 and a bigger size $30 both from Radioshack.
BTW, about antennas, on 5GHz we've been able to send a videoclip with
0dBm output power, using 18dBi gain antenna... and we do it just for
fun.
Using the powerfull 2.4Ghz DSP from the world.
:)
Vasile

2006\09\30@135439 by Russell McMahon

face
flavicon
face
>>I'll point out too, that you can do anything you like to the
>>RECEIVER, and
>>stay within part 15.

> NO NO NO..........first of all, it's NOT part 15!

> Also, the receiver and/or receiving antennas cannot be modified
> either because type acceptance certification will be invalidated.
> So,
> to stay within the ISM service guidelines, you cannot modify the
> receiver or antenna either.

No need. You can legally build a receiver preamp or use a dish to feed
a preamp. While IANAL, I ssert that if you have a received that sits
electrically "very close" to the output of this it could be done
legally without touching the receiver, or modifying its aerial or
violating type approval.

> Personally, I wouldn't amplify a SAW based transmitter and I think
> they should be disallowed even on low power transmitters on UHF
> frequencies.

Nah. They can't be any worse than a well maintained rotary spark gap.


       Russell

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