[hfsig] Sidebands on Raspberry Pi WSPR carrier

Ron Ott ronott at sbcglobal.net
Sun Sep 4 16:42:33 CDT 2016


Robert - 
I think we can agree that the USB power source per se is not the cause of the 120 Hz sidebands, we've tried different power sources including a battery pack and a well regulated commercial power supply that did not eliminate the problem.
You have to take a report of a spurious signal on 40m with caution:  If a listener forgets to switch bands in his WSPR or WSJT-X software, you will be spotted on the band that he last listened to instead of the band you are on.  Use an SDR receiver or spectrum analyzer to monitor for spurious signals. Since I just got my RPi on the air yesterday, I haven't looked for harmonics yet, and it was the duplicate concurrent spots on two  frequencies (like those reported by Brad) that made me look at my sidebands.  I can even see second-order sidebands 240 Hz from the carrier on my WSJT-X waterfall display, but they're too far away to decode.
The daughter card filter is not sharp enough to eliminate close-in sidebands, but I think it should handle sub harmonics and super harmonics though.  I think there is a plot of the passband available as a link from the TAPR webpages.
I think I'll drop a note to James, who wrote the WSPR code for RPi and ask whether this has been an ongoing issue.  Good to know that it happens with early RPi models too, more people will be interested in a solution.
Thanks, Ron / W6XY

      From: Robert Palmer <repx2 at bellsouth.net>
 To: 'TAPR HF Modes SIG Mailing List' <hfsig at tapr.org> 
 Sent: Sunday, September 4, 2016 10:58 AM
 Subject: Re: [hfsig] Sidebands on Raspberry Pi WSPR carrier
   
#yiv4230805716 #yiv4230805716 -- _filtered #yiv4230805716 {font-family:Helvetica;panose-1:2 11 6 4 2 2 2 2 2 4;} _filtered #yiv4230805716 {panose-1:2 4 5 3 5 4 6 3 2 4;} _filtered #yiv4230805716 {font-family:Calibri;panose-1:2 15 5 2 2 2 4 3 2 4;} _filtered #yiv4230805716 {font-family:Times;panose-1:2 2 6 3 5 4 5 2 3 4;}#yiv4230805716 #yiv4230805716 p.yiv4230805716MsoNormal, #yiv4230805716 li.yiv4230805716MsoNormal, #yiv4230805716 div.yiv4230805716MsoNormal {margin:0in;margin-bottom:.0001pt;font-size:12.0pt;}#yiv4230805716 a:link, #yiv4230805716 span.yiv4230805716MsoHyperlink {color:blue;text-decoration:underline;}#yiv4230805716 a:visited, #yiv4230805716 span.yiv4230805716MsoHyperlinkFollowed {color:purple;text-decoration:underline;}#yiv4230805716 span.yiv4230805716EmailStyle17 {color:#1F497D;}#yiv4230805716 .yiv4230805716MsoChpDefault {font-size:10.0pt;} _filtered #yiv4230805716 {margin:1.0in 1.0in 1.0in 1.0in;}#yiv4230805716 div.yiv4230805716WordSection1 {}#yiv4230805716 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,  RobertN8QB    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>
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    
_______________________________________________
hfsig mailing list
hfsig at tapr.org
http://www.tapr.org/mailman/listinfo/hfsig


_______________________________________________
hfsig mailing list
hfsig at tapr.org
http://www.tapr.org/mailman/listinfo/hfsig


   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tapr.org/pipermail/hfsig/attachments/20160904/b8493e37/attachment-0001.html>


More information about the hfsig mailing list