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'[PIC]: UHF Transmission'
2001\10\21@113507 by brah

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I'm transmitting data from PIC to PIC via separate 433MHz rx and tx
boards.
Does anyone know a source of antenna relays that can be switched
rapidly, say two or four times a second, and have a long life span at
that rate?
Is there any such thing as solid sate relays that would do this?
Power is lo, 2mW.
Regards Howard.

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2001\10\21@120520 by Martin Wehner

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Hello Howard-

unfortunately, I do not have the answer to your question.
I myself have tested RF transmission between PICs and have a few questions
regarding your setup (if you don't mind):
-What transmitter/receiver modules are you using?
-What protocol do you use to transmit the data between the PICs?
-How far apart can the PICs be currently (w/o ant) for you to reliably receive
the data?
-What is the expected range once you hook up the proper antennas?
-Are your devices FCC compliant? If not, are you planning on getting them
certified?

If you do have the time, I would greatly appreciate answers to the questions
above.
Thank you so much & good luck with finding the antenna switch!

       Martin




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2001\10\21@131726 by Chris Carr

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www.aurel.it/homepage.htm

Click on "Wireless"
Then Select in Download Area (RH Side) "Short Form, Application
Notes......."

Then Scroll down the list and almost at the bottom you will find
650200437 RT Switch
Click on the 1st pdf symbol for the Short Form Description 2nd for the App
Note

Regards

Chris Carr


{Original Message removed}

2001\10\22@080039 by Russell McMahon

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> I'm transmitting data from PIC to PIC via separate 433MHz rx and tx
> boards.
> Does anyone know a source of antenna relays that can be switched
> rapidly, say two or four times a second, and have a long life span at
> that rate?
> Is there any such thing as solid sate relays that would do this?
> Power is lo, 2mW.
> Regards Howard.


This may be overkill but a small reed relay would work well - as would most
small relays.
Reeds may be purchased bare and have suitable coils added (Jaycar sell some)
or small complete reed relays are available. These have very fast switching
times and will handle power levels well above what you need. Using a double
pole changeover relay would allow grounding of the receiver input during
transmit.

You could also make a PIN diode TR switch (see amateur radio handbooks for
details) - these should be very easy at the power levels you are dealing
with. I suspect that using 1N4148 diodes would work OK.
Basically these consist of two diodes in series with the transmit and
receive lines with the eg cathodes of both diodes facing each other .
Positive DC is fed to the two anodes via RFCs. RF is also fed to one diode's
anode and the aerial connected to the other anode.
When the centre points (two cathodes) are not connected to any other device
the diodes block and the switch is "off". If you now ground the centre point
via an RFC BOTH diodes conduct DC and the RF can flow through BOTH diodes.
The DC bias voltage has to be in excess of the peak RF voltage (easy in this
case) so that the diodes are not placed into reverse blocking by the RF
voltage. For better isolation it is also possible to shunt the receiver
input to ground with a similar arrangement during transmit. With such an
arrangement it is possible to make receivers that can listen BETWEEN the
Morse code dots when sending Morse - this gives some idea of the achievable
response times.





       Russell McMahon

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2001\10\22@085032 by brah

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Martin Wehner wrote:
>
> Hello Howard-
>
> unfortunately, I do not have the answer to your question.
> I myself have tested RF transmission between PICs and have a few questions
> regarding your setup (if you don't mind):
> -What transmitter/receiver modules are you using?
> -What protocol do you use to transmit the data between the PICs?
> -How far apart can the PICs be currently (w/o ant) for you to reliably receive
> the data?
> -What is the expected range once you hook up the proper antennas?
> -Are your devices FCC compliant? If not, are you planning on getting them
> certified?

- Elsema rx and tx modules (http://www.elsema.com)
- Own version. rx has data slicer, which demands 50% duty cycle. I'm
trying 300/300uS and 150/150uS for 1's and 0's.  Detection is by
determining length of a hi or lo of the bit (doesn't matter which, as
both are the same)
-I have had them workinbg one way (no antenna switch) over a few yards
with a short wire as an antenna.
-I'm looking/hoping for at least 1000 yards over open spaces.
-the devices are compliant in Australia.
Howard
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2001\10\22@094544 by t F. Touchton

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A common method is to use a PIN diode switching circuit.  The Agilent web
site has many PIN diodes and application notes.

You could also use a diplexor arrangement if you stagger your transceiver
frequencies.

Scott



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I'm transmitting data from PIC to PIC via separate 433MHz rx and tx
boards.
Does anyone know a source of antenna relays that can be switched
rapidly, say two or four times a second, and have a long life span at
that rate?
Is there any such thing as solid sate relays that would do this?
Power is lo, 2mW.
Regards Howard.

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2001\10\22@120338 by Gordon Varney

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Part Number MSW-2-20 Mini-circuits http://www.minicircuits.com

Gordon Varney

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