[Lowfer] Bogus WSPR decodes

[John Andrews]

Paul,

> But with WSPR, BPSK, WOLF and other
> modes phase shift at a single freq on audio would be easy.Would it be a
> practical project to make a phasing exciter for single tone or a narrow
> audio bandpass? I know simple designs exist for simple SDR exciters but I am
> thinking of  a stand alone unit? What do you think?

Yes, you can definitely make an accurate audio phase shift network more 
simply for a narrow BW than a wide one. A good free design program for 
op-amp all-pass filters is:
http://www.werewoolf.org.je/apf.htm

With that program, you can play with the component values to your 
heart's content. 30 dB opposite sideband rejection is trivial. 40 dB can 
be done with standard 1% tolerance parts. 50 dB requires accurate 
measurement of actual 1% parts values, and a pile of parts from which to 
choose. At the 1 watt transmitter output level, 30-40 dB suppression 
should be plenty. I would suggest FET-input op-amps like TL072/074 or 
TL082/084. Avoid antiques like LM324's or 741's.

With WSPR requiring 1400-1600 Hz tones, you could probably restrict 
yourself to the 1000-2000 Hz range. This would mean setting WOLF or PSK 
up for 1500 Hz or so, no problem.

JA