On November 25, 2005 04:29 pm, Vitaliy wrote:
> Hi List,
>
> About ten years ago I built a simple super-regenerative FM receiver,
> which worked remarkably well, considering that I used a single
> transistor and maybe eight passives. I was wondering if I can build a
> quick-and-dirty wireless modem based on a super-reg, a one-transistor
> AM transmitter, and a modem IC.

Sure you can.
You just finished saying you built a receiver 10 years ago.

> I have a project that requires a speed of only 1200 baud, half
> duplex, and a range of 10-15 meters. Frequency stability is a
> priority.

Sounded okay until you said frequency stability is a priority, which 
frequency needs to be stable? the regen or the 1200baud?

If you meant the regenerative receiver, no, you can't because by nature 
a regen receiver locks to the strongest transmission, which is not 
necessarily your own transmitter.
If you meant the 1200baud, then that is dictated by the transmitter 
unless your receiver is made to create it's own 1200baud for "no 
signal".

> I was looking at the TCM 3105 (which is relatively expensive despite
> its age, btw), and remembered how Russel suggested a while back that
> one could use a DTMF circuit instead of a "real" modem IC. What are
> your thoughts on that? What is the highest baud rate that one can
> theoretically achieve with a DTMF chip?

Have your TX circuit send AM as you planned, and have your receiver 
receive AM and send the AM into a comparator (some PIC chips have 
comparators built in, for example pic16c620 ....but choose a more 
updated chip since the 620 is no longer built).
Then have your pic chip generate the 1200baud.

> Or maybe there are less expensive real modem ICs out there?

Probably, but I didn't look at any of the suggestions mentioned below.

> Alison Lewis wrote:
> > If you've been watching, there were some great RF
> > devices suggested to me, so I put the list together
> > for anyone else who may be looking for small RF
> > transmitters. I went with
> > http://www.rentron.com/remote_control/TXLC-315.htm.
> >
> >
> > www.sparkfun.com
> > http://www.radiotronix.com/products/prodrctas.asp
> > http://www.rentron.com/remote_control/TXLC-315.htm or
> > http://www.rentron.com/remote_control/TXLC-434.htm
> > www.rfsolutions.co.uk
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