[hfsig] Sidebands on Raspberry Pi WSPR carrier

Ron Ott ronott at sbcglobal.net
Sun Sep 4 12:00:06 CDT 2016


Brad -  
That's the symptom: dual decodes, one is the carrier and the other is one of the sidebands.  If you're using WSJT-X and have the waterfall display on, you can clearly see both sidebands at the bottom of the panel.  In your case it appears that the sideband is only 5dB down from the carrier; but the way WSJT-X arrives at the S/N is a bit mysterious. A spectrum analyzer or using Sprectravue with an SDR would be a better measure of the sidebands.  Note that the sideband and carrier are exactly 120 Hz apart.
I'm using my RPi attached to the back of the "official" touchscreen display and am wondering whether a 120 Hz scan signal is modulating the carrier. Is you RPi in a separate box, away from the monitor?
Ron, W6XY

      From: Brad Farr <taprsig at unsupported.org>
 To: TAPR HF Modes SIG Mailing List <hfsig at tapr.org> 
 Sent: Sunday, September 4, 2016 7:06 AM
 Subject: Re: [hfsig] Sidebands on Raspberry Pi WSPR carrier
   
I'm new at this, but I observed the same thing in my initial testing, and was about to ask the same question.
An example:
>From the raspberry pi -
Desired center frequency for WSPR transmission: 14.097166 MHz  Waiting for next WSPR transmission window...  Obtained new ppm value: 1.16522  TX started at: UTC 09-04-2016 13:38:01.002  TX ended at:   UTC 09-04-2016 13:39:51.679 (110.678 s)
And what I decoded -
1338  -26  -0.9   14.097006   -1   KW1BF         DN41     101338  -21  -0.9   14.097126   -1   KW1BF         DN41     10
Some details -Raspberry Pi 2, the TAPR wspr board is connected via coax to an OCF dipole (an MFJ-2012), but I observed the same thing with a piece of random wire.For receiving I used a Sony ICF-2010, in the same room as the raspberry pi, with no external antenna, and with the built in telescoping antenna fully retracted and folded. The local/DX attenuator switch set to local, and RF gain slider at about midpoint. Dial frequency 14095.6 kHz, USB mode. Using WSPR-X on a Mac.
If there are other things I should try or observations I should report, please let me know.
Thanks,Brad


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