[aprssig] RFM Xcvr chips for cheap FM voice?

Stephen H. Smith wa8lmf2 at aol.com
Thu Jun 20 20:23:20 CDT 2013

On 6/20/2013 1:01 PM, Robert Bruninga wrote:
> Has anyone hooked up an amplified speaker to the output of one of these
> Argent Data Systems RFM12BP 500mW Data Transceiver - 433 MHz and talked to
> it in FM voice?
> The idea of a postage stamp 70cm voice transceiver can have some ham radio
> uses I think.
> It is FM so why wouldn't it work for sound unless the data inputs and
> outputs are hard limited and driven into a data-limitesr before the input
> and output.
> It has a lot of pins.  I wonder if any of them give access to the analog
> side.
> These are common RFM chips, but Argent Data's is a high power one (0.5W).
> Curious...
> Bob, WB4APR
> _______________________________________________

Normally these things don't have any FM pre-emphasis on TX and de-emphasis on 
RX, and they have no mic preamp/deviation limiter/clipper.  Assuming you fed 
some sort of amplified high-level-output mic directly into their modulator, 
it's going to sound horrible in a normal voice receiver at the other end -- 
muffled, muddy and lacking in highs after the receive end de-emphasizes a flat 
response signal.

You'd have to kludge a bunch of external circuitry to make them useable on 

Easier (and probably cheaper) to just use a cheap Chinese hand-held on lowest 



Stephen H. Smith    wa8lmf (at) aol.com
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