> For a digital circuit, yes, there is slightly more.
> An AGC is needed unless you do FM (my preference would be to send
> 2-tones-FSK and then use the PIC to differentiate the 2-tones, this way
> the AGC is useful but isn't as critical).

AGC is useful, and it's cheap -- so I am planning to use it.

> Radio passes through walls.

Yes, I noticed. ;)

> Your 100mW may still be overshadowed by a transmitter a mile away
> pumping out 5W....

Wow, you are right! I should have done my homework... this goes against my 
intuition:

100 mW / (10 m)^2 = 1 mW/m^2
5000 mW / (1609 m)^2 = 1.9 mW/m^2

> unless your frequency of choice is dedicated to
> low-power stuff, for example garage-door openers or particular bands
> like that. If you use those bands, then, yes, you're likely okay.

Alright. Where would I find a list of such frequencies, and how would I know 
what would make it legal to transmit at those frequencies (output power, 
antenna length)?

> I'm not sure why you need freq stability.

I haven't done anything wireless for a long time, but I do remember how I 
had to constantly adjust the trim cap (or stretch/compress the coil) to 
compensate for frequency shift due to differences in temperature. That's 
what I meant by frequency stability -- not having to tune the Tx/Rx modules 
every time I need to use them.

> AM is what I thought you meant from your original posting.
> FM FSK PSK is much much better, so I'm glad you chose it.

Yes, I meant "AM modulated carrier."

> Well, it is the piclist, so it was a guess a pic was needed here, but
> something in your circuit needs to deal with radio noise, be it the
> black-box, the pic, or the terminal at the end of the 1200baud.

I was surprised to find that there isn't much choice when it comes to 1200 
baud modems. TCM3105 seems to be the easiest one to use, unfortunately the 
datasheet says "Full Duplex up to 1200 Tx and 150 Rx"

I was planning to use it with a circuit which automatically echoes back 
whatever it receives, so I need FD at 1200 baud both ways. It seems that my 
only choice at this point is to use XR2206 and XR2211.

--- took a break to do more Googling --- 

What if I use an rfPIC, and a stand-alone RF receiver (e.g., rfRXD0420)?

Vitaliy 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist