[aprssig] BPSK decoding

[Stephen H. Smith]

scott at opentrac.org wrote:
> I've had PSK31 code working on the OpenTracker for some time now, but as far
> as I know, there's no inexpensive hardware-based demodulator for the mode.
> Your options seem to be either a soundcard or an expensive multimode TNC.
>
> Is there a simple circuit somewhere for single-channel BPSK demodulation?
> Specifically, can it be done with an XR2211?  Seems like you ought to be
> able to have it track the carrier frequency and use the phase detect output
> to detect the 180-degree phase reversals.  Or does that cause the '2211 to
> lose lock for too long?
>
> I think it'd be cool to have a PSK31 QRP rig for backpacking that'd do APRS
> and hook up to a PDA for text messaging.
>
> Scott
> N1VG
>
>   


Not sure it would be practical.   You often have dozens of simultaneous 
PSK31 carriers in the 2.5 KHz audio passband of the typical HF SSB 
rig.    You typically leave the radio on a fixed RF frequency, and tune 
in the desired  PSK31 signal by clicking on it's trace on an spectrum 
analyzer display displaying the baseband output of the USB product 
detector; i.e. by varying the AUDIO center frequency of the PSK 
detector.   Even the WinWarbler dedicated PSK31  transceiver is 
basically a single-channel crystal-controlled USB transceiver that 
assumes the PSK signal selection will be done at base band; i.e. by 
tuning audio freqs. 

What is an XR2211 going to do when presented with 5 or 10 different 
phase-shifting tones simultaneously?







--

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com


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