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From: dpalmer@csuohio.edu (Darryl Palmer)
Subject: Re: REQUEST: Simple Single Channel 27MHz TX/RX circuit diagram
Message-ID: <1994Jul7.171732.13497@news.csuohio.edu>
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Date: Thu, 7 Jul 1994 17:17:32 GMT
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Wally Blackburn (wrb@ccsitn.cb.att.com) wrote:
: Since we're on the subject of wireless data links:

: I've been toying with the idea of a wireless data link along the lines of
: the one in Jan Axelson's MicroComputer Journal article.  She used a pair of
: Ramsey FM-10 transmitters and cheap FM radios with some AM7910 modem chips.
: Anyway, I've been looking at that and other possibilities and I came across
: the Holtek tx/rx boards in the Digi-Key catalog.

: They have a 310 MHz serial data input AM SAW transmitter for $17.16 and a
: companion receiver for $20.30.  So I said "Bloody hell, why am I messing
: around trying to build a 1200 baud link for $100 when I can buy these
: things for about $40?!"

: Has anybody used them?  What is the max data rate?  What is range like?

: PS.  They also have an FM pair for TX: $50.09, RX: $62.64.  Any experience
:      with these?

: -- 
:    Wally Blackburn		   Clinton-Gore - Socialist Leadership
:    wrb@ccsitn.cb.att.com		          for the 90s!
:    Amateur Radio Station AA8DX	   I'm the NRA.
:    '91 FXR	DoD #1375

I used these kits (Actually the kits are not made by Holtek, they are made by
Ming but they use Holtek chips) for an e-stop for the AUVS ground competition.
When we measured out the distance it was around 120+ ft.  As far as data rate,
I haven't tested it but I remember reading that the "code" signal has to
be valid for a little while, like 1/2 seconds, before it would latch the
data pins for you.  There are 4 bits of data if you use an 8 bit code with
a relay already built in for driving things (We used it with a relay) or
you can use the other chip they provide to get a 12 bit code and a relay 
output.  If you think you are going to get it, I will check on the supplier
we went with. They offered the TX, RX, and also keychain TX for only 40+
bucks.  The keychain only allows you to transmit 1 or 2 bits, but it is 
really small.

The 120 ft we got with the kits were with the antennae they provided (One
internal PCB trace for the transmitter and I think a 1/4 wave for the
receiver), but if you go with a full wave or a real TX antenna you could
increase the distance.  If you are going to use this, I have to repeat
what the docs said, THIS UNIT IS FOR EXPERIMENTAL PURPOSES AND IS NOT FCC
TESTED.  Like it made a difference to me.



Darryl Palmer
Grand Poobah and President
IEEE Student Chapter
Cleveland State University
