[hfsig] Sidebands on Raspberry Pi WSPR carrier

Robert Palmer repx2 at bellsouth.net
Sun Sep 4 12:58:01 CDT 2016


Gentlemen,

I wanted to chime-in to say that I too have noticed the sidebands on 20m using the WsprPi daughtercard.  I have 2 of the cards and both exhibit that charateristic.  I have tried several USB power supplies as well as with a USB battery pack, which was slightly cleaner but not by much.

 

Separately I am curious if any of you have noticed spurious signals outside the 20m band using the WSPR Pi?  I was somewhat concerned to see on the wsprnet.org map that I was heard on 7.04 MHz, but I have never intentionally transmitted WSPR on 40m.  This was using a multiband OCF dipole which could have played a part in the 40m anomaly.  (I have since switched to a 20m hamstick dipole and no longer heard on 40m so far.)

 

After noticing the 40m anomaly, I checked the waterfall display for 10m and noticed there is a strong signal at ~28.194 MHz.  As info, I am running a Pi v 1B+ with Wifi dongle and USB battery (no kbd, mouse, display)…

 

73,

 

Robert

N8QB

 

 

From: hfsig [mailto:hfsig-bounces at tapr.org] On Behalf Of Ron Ott
Sent: Sunday, September 4, 2016 12:00
To: TAPR HF Modes SIG Mailing List <hfsig at tapr.org>
Subject: Re: [hfsig] Sidebands on Raspberry Pi WSPR carrier

 

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 <mailto:taprsig at unsupported.org> >
To: TAPR HF Modes SIG Mailing List <hfsig at tapr.org <mailto: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     10

1338  -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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