<p dir="ltr">Ron & folks, one more observation. When i ran the Pi in a motel room this Spring, i used a 9:1 balun to a longwire and (carefully) ran a short wire to the 3rd prong of the electrical outlet. (I bought a plug, wired it and put Shoe Goo in there to immobilize the wire.) After verifying that there was zero ohms between the electrical ground and the cold water pipe.</p>
<p dir="ltr">The Pi kind of freaked out, spewing thousands of lines of nonsense in the terminal window. I hastily shut it off and removed the ground wire.</p>
<p dir="ltr">Then, back home, using the electrical ground as my station ground for my FT-857D resulted in my hearing some hum on receive.</p>
<p dir="ltr">The hum went away when i ran the station ground to the toilet water pipe, which also had zero ohms with electrical ground.</p>
<p dir="ltr">Orrin wn1z in CN90</p>
<div class="gmail_extra"><br><div class="gmail_quote">On Sep 5, 2016 12:42, "Ron Ott" <<a href="mailto:ronott@sbcglobal.net">ronott@sbcglobal.net</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div style="color:#000;background-color:#fff;font-family:times new roman,new york,times,serif;font-size:16px"><div><span>Hi Orrin. That's true if your signal is always 20-25dB below the peak noise level (as WSPR reports signal levels), but more local receivers will hear and be able decode multiple concurrent signals as I did last night. Technically, these sidebands are not FCC acceptable, although it's difficult to get worked up over a 100mW transmitter with spurious sidebands. </span></div><div><span><br></span></div><div dir="ltr"><span>I appreciate your comment about the apparent isolation of your RPi from grounds, including the antenna. I'll run that experiment today using my own station; I can confidently say that I am sideband free when I run the RPi into a 50-ohm dummy load that is isolated from any grounds and I'm hoping an isolation balun will be the cure.</span></div><div dir="ltr"><span><br></span></div><div dir="ltr"><span>73, Ron/W6XY</span></div><div><br><br></div><div style="display:block"> <div style="font-family:times new roman,new york,times,serif;font-size:16px"> <div style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px"> <div dir="ltr"> <font size="2" face="Arial"> <hr size="1"> <b><span style="font-weight:bold">From:</span></b> Orrin Winton <<a href="mailto:orrin.winton@gmail.com" target="_blank">orrin.winton@gmail.com</a>><br> <b><span style="font-weight:bold">To:</span></b> TAPR HF Modes SIG Mailing List <<a href="mailto:hfsig@tapr.org" target="_blank">hfsig@tapr.org</a>>; Orrin Winton <<a href="mailto:orrin.winton@gmail.com" target="_blank">orrin.winton@gmail.com</a>> <br> <b><span style="font-weight:bold">Sent:</span></b> Monday, September 5, 2016 12:29 PM<br> <b><span style="font-weight:bold">Subject:</span></b> Re: [hfsig] Sidebands on Raspberry Pi WSPR carrier<br> </font> </div> <div><br><div><div><div dir="ltr">Hmm, my 20m antenna is only for the Pi. It is not connected to any ground.</div>
<div dir="ltr">The 2A power supply for the Pi is 2-prong. The 3rd prong (ground) is not used.</div>
<div dir="ltr">Power out is 90-100mW.</div>
<div dir="ltr">And i get the sidebands. I'm not overly concerned. Maybe i should be; i don't know. The sidebands are -15dB from my main signal, and the reception reports i get (on <a rel="nofollow" shape="rect" href="http://wspr.aprsinfo.com/" target="_blank">wspr.aprsinfo.com</a>) are -20 to -25, with no duplicates that i can see, so i doubt anyone is hearing the sidebands.</div>
<div dir="ltr">Orrin wn1z</div>
<div><br clear="none"><div>On Sep 5, 2016 09:11, "Ron Ott" <<a rel="nofollow" shape="rect" href="mailto:ronott@sbcglobal.net" target="_blank">ronott@sbcglobal.net</a>> wrote:<br clear="none"><blockquote style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div><div style="color:#000;background-color:#fff;font-family:times new roman,new york,times,serif;font-size:16px"><div><br clear="none"></div><div style="line-height:19.52px"><span style="line-height:1.22em">Last night I completed some revealing tests with the Raspberry Pi (=RPi) TX with TAPR 20m WSPR kit. <b>The bottom line is that grounds are the cause of the observed spurious sidebands.</b></span></div><div style="line-height:19.52px"><span style="line-height:1.22em"><br clear="none" style="line-height:1.22em"></span></div><div dir="ltr" style="line-height:19.52px"><span style="line-height:1.22em">* I see no sidebands when the TX is connected to a 50-ohm load and my HP scope with a <i style="line-height:1.22em">floating ground </i>input. I'm receiving on an SDR with an outside 20m vertical antenna, picking up stray RF. In this setup the RPi TX is fully isolated from any grounds in the shack.</span></div><div dir="ltr" style="line-height:19.52px"><span style="line-height:1.22em"><br clear="none" style="line-height:1.22em"></span></div><div dir="ltr" style="line-height:19.52px"><span style="line-height:1.22em">* When I move the 50-ohm load to the input of an HP frequency counter with a grounded-shield (1Mohm) input, I see several sidebands on the carrier that are multiples of 60Hz. In this setup the shield side of the RF output coax is connected to the mains ground through the frequency counter. I decoded four (4) WSPR signals simultaneously - the carrier and three of the sidebands. </span></div><div dir="ltr" style="line-height:19.52px"><span style="line-height:1.22em"><br clear="none" style="line-height:1.22em"></span></div><div dir="ltr" style="line-height:19.52px"><span style="line-height:1.22em">* I played with ground leads to the RPi USB connector shells and to the ground side of the RF output terminal strip, but there was no change in the sidebands. Since the RPi is a small computer, the grounds are not that easy to discern and it may take some experimenting to discover what works. </span></div><div dir="ltr" style="line-height:19.52px"><span style="line-height:1.22em"><br clear="none"></span></div><div dir="ltr" style="line-height:19.52px"><span style="line-height:1.22em">*<b> Potential solutions</b>: Perhaps running the antenna lead directly to the transmitter without a ground connection in the shack might help - an experiment for tomorrow. An un/un transformer might be used to isolate the RPi grounds from the shack ground and avoid the ground loops. I'll look into making an un-un myself or buying a commercially built one from Balun Designs.</span></div><div dir="ltr" style="line-height:19.52px"><span style="line-height:1.22em"><br clear="none" style="line-height:1.22em"></span></div><div dir="ltr" style="line-height:19.52px"><br clear="none"></div><div dir="ltr" style="line-height:19.52px">Ron, W6XY</div><div dir="ltr"><br clear="none"></div></div></div></div><br clear="none">______________________________ _________________<br clear="none">
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