Bob:

I agree, its not worth modifying the walkie talkie if a
data-to-voice encoder and voice-to-data decoder exist
that can reasonably transmit over a walkie talkie's
channel. Would love to review some of references on
software or studies done already. Thanks so much in
advance.

Ben

Bob Bob wrote:
Hi Ben

Modifying the walkie talkie itself is probably way too cost prohibitive.
It is much cheaper to use a PC (eg laptop or maybe PDA) to do the
necessary encoding/decoding of digital information. I'd suggest a
soundcard interface rather than purpose built hardware like a TNC. You
can even acoustically couple but you may have to lower the data rate some.

Your next hurdle will be the much lower data rate of an essentially
voice bandwidth radio and thus the slower transfer of images/data.
Without a huge amount of trouble you may get 1200-2400 bits per second
on a voice FM circuit. This works out at around 100-200 characters per
second which for an average 640x480 lowish quality JPG image (say 30K
bytes) as taking quite a while to transmit. (Say 3-5 mins)

Cell phones have a much higher data rate and in fact encode audio into a
digital stream. I'll admit I dont know what the rate is but think 3G is
around 2MBit/sec max!

You could no doubt modify the walkie talkie modulation method and
bandwidth to get better rate but I doubt it would be worth it. I'll not
mention the legal implications of doing this! If you really want to play
have a look at the ISM bands like 2.4GHz. In the US at least you can
even build your own equipment that conforms to this "unlicensed" band.
There are even chips available to make it easier.

There is lots of GPL software around that will encode/decode an audio
stream to/from data and even key the TX. If you want some names/refs pls
post your request.

Cheers Bob VK2YQA


wrote:


Wireless image transmission over walkie-talkie; has this
been done?