<html><head></head><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:16px"><div id="yui_3_16_0_ym19_1_1473090208826_81361" dir="ltr"><span id="yui_3_16_0_ym19_1_1473090208826_81501">Postscrpt -- If you decide to build your own balun, I just realized that 30 turns of 30ga wire may be too much inductance at 20m. I would think that 5 turns for the primary and secondary each would work better, but you would lose LF capability. You could use 5 turns of larger diameter wire for 20m and handle more power for larger QRP projects.</span></div><div id="yui_3_16_0_ym19_1_1473090208826_81361" dir="ltr"><span><br></span></div><div id="yui_3_16_0_ym19_1_1473090208826_81361" dir="ltr"><span id="yui_3_16_0_ym19_1_1473090208826_81624">Ron/W6XY</span></div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1473090208826_81447"><br></div><div class="yahoo_quoted" id="yui_3_16_0_ym19_1_1473090208826_81451" style="display: block;"> <div style="font-family: times new roman, new york, times, serif; font-size: 16px;" id="yui_3_16_0_ym19_1_1473090208826_81450"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;" id="yui_3_16_0_ym19_1_1473090208826_81449"> <div dir="ltr" id="yui_3_16_0_ym19_1_1473090208826_81448"> <font size="2" face="Arial" id="yui_3_16_0_ym19_1_1473090208826_81455"> <hr size="1" id="yui_3_16_0_ym19_1_1473090208826_81547"> <b><span style="font-weight:bold;">From:</span></b> Ron Ott <ronott@sbcglobal.net><br> <b><span style="font-weight: bold;">To:</span></b> TAPR HF Modes SIG Mailing List <hfsig@tapr.org> <br> <b><span style="font-weight: bold;">Sent:</span></b> Monday, September 5, 2016 11:40 AM<br> <b><span style="font-weight: bold;">Subject:</span></b> Re: [hfsig] Sidebands on Raspberry Pi WSPR carrier - how to build an ground isolation balun<br> </font> </div> <div class="y_msg_container" id="yui_3_16_0_ym19_1_1473090208826_81452"><br><div id="yiv6881123364"><div id="yui_3_16_0_ym19_1_1473090208826_81454"><div style="color:#000;background-color:#fff;font-family:times new roman, new york, times, serif;font-size:16px;" id="yui_3_16_0_ym19_1_1473090208826_81453"><div id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885"><br clear="none"></div><div id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885">I've been researching baluns with DC input-output isolation to eliminate the AC modulation of the RPi WSPR carrier. Simply, this is a transformer with a primary and secondary wound on a ferrite toroid core with no common DC connection between the input and output windings. Here is an article on how to build an isolation transformer that works down to LF, in case Zoltan designs a TAPR project board for 437kHz.</div><div id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885"><br clear="none"></div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885"><a rel="nofollow" shape="rect" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_73993" target="_blank" href="http://www.amrad.org/projects/lf/lf_isolation/">LF Isolation Transformer | AMRAD</a><br clear="none"></div><div class="yiv6881123364link-enhancr-attachment yiv6881123364link-enhancr-element yiv6881123364richcompose-card" id="yiv6881123364enhancrCard_0" style="width:450px;font-family:'Georgia', 'Times', 'Times New Roman', 'serif';margin-top:5px;margin-bottom:5px;background-color:#ffffff;"><table class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74628" cellspacing="0" cellpadding="0" border="0" style="width:450px;min-height:auto;position:relative;display:block;"><tbody id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74627"><tr class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74633"><td colspan="7" rowspan="1" class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74632" style="min-height:1px;background-color:#e5e5e5;font-size:1px;border-collapse:collapse;"><div class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74631" style="min-height:1px;background-color:#e5e5e5;font-size:1px;line-height:0px;"> </div></td></tr><tr class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74816"><td colspan="1" rowspan="5" class="yiv6881123364link-enhancr-element" style="width:1px;background-color:#e5e5e5;font-size:1pt;border-collapse:collapse;"><div class="yiv6881123364link-enhancr-element" style="width:1px;background-color:#e5e5e5;font-size:1pt;"> </div></td><td colspan="1" rowspan="5" class="yiv6881123364link-enhancr-element" style="width:14px;background-color:#ffffff;font-size:0pt;border-collapse:collapse;"><div class="yiv6881123364link-enhancr-element" style="width:14px;background-color:#ffffff;font-size:14pt;"> </div></td><td colspan="2" rowspan="1" class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74878" style="min-height:6px;background-color:#ffffff;font-size:0pt;border-collapse:collapse;"><div class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74877" style="min-height:6px;background-color:#ffffff;font-size:6pt;"> </div></td><td colspan="1" rowspan="5" class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74815" style="width:20px;background-color:#ffffff;font-size:0pt;border-collapse:collapse;"><div class="yiv6881123364link-enhancr-element" style="width:20px;background-color:#ffffff;font-size:20pt;"> </div></td><td colspan="1" rowspan="5" class="yiv6881123364link-enhancr-element" width="1" style="width:1px;background-color:#e5e5e5;font-size:1pt;border-collapse:collapse;"><div class="yiv6881123364link-enhancr-element" style="width:1px;background-color:#e5e5e5;font-size:1pt;"> </div></td></tr><tr id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74626"><td colspan="2" rowspan="1" class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74625" style="width:100%;vertical-align:middle;font-family:'Georgia', 'Times', 'Times New Roman', 'serif';"><div class="yiv6881123364link-enhancr-text-part yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74624" style="line-height:16.5px;background-color:#ffffff;width:414px;"><div class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74623" style="word-wrap:break-word;"><span class="yiv6881123364link-enhancr-element yiv6881123364icon yiv6881123364icon-shrink yiv6881123364link-enhancr-toggle" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74814"></span><span class="yiv6881123364link-enhancr-element yiv6881123364icon yiv6881123364icon-close yiv6881123364link-enhancr-delete" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74630"></span><a rel="nofollow" shape="rect" class="yiv6881123364link-enhancr-card-urlWrapper yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74813" target="_blank" href="http://www.amrad.org/projects/lf/lf_isolation/" style="text-decoration:none;text-decoration:none;color:#000000;line-height:100%;font-size:18px;display:block;"><span class="yiv6881123364link-enhancr-element yiv6881123364link-enhancr-card-title" style="margin:0;font-weight:normal;margin-bottom:3px;font-size:18px;line-height:21px;max-height:43px;color:#000000;overflow:hidden;display:inline-block;">LF Isolation Transformer | AMRAD</span></a><div class="yiv6881123364link-enhancr-card-description yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74622" style="font-size:13px;line-height:20px;color:#999999;max-height:81px;font-family:'Georgia', 'Times', 'Times New Roman', 'serif';overflow:hidden;">LF Isolation Transformer INTRODUCTION The power supplies in the receivers and other loads will create small amounts of pulse currents with harmonics reaching into the LF band of interest. </div></div></div></td></tr><tr id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74812"><td colspan="2" rowspan="1" class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74811" style="min-height:6px;background-color:#ffffff;font-size:0pt;border-collapse:collapse;"><div class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74810" style="min-height:6px;background-color:#ffffff;font-size:6pt;"></div></td></tr><tr id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_75003"><td colspan="1" rowspan="1" class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_75032" style="vertical-align:middle;font-family:'Arial', 'Helvetica Neue', 'Helvetica', 'sans-serif';"><div class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_75031" style="font-size:0pt;"><a rel="nofollow" shape="rect" class="yiv6881123364link-enhancr-card-url yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_75030" target="_blank" href="http://www.amrad.org/projects/lf/lf_isolation/" style="color:black;text-decoration:none;text-decoration:none;cursor:pointer;"><span class="yiv6881123364link-enhancr-element yiv6881123364link-enhancr-view-on" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74009" style="display:inline-block;line-height:11px;max-width:314px;min-width:254px;overflow:hidden;max-height:13px;"><span class="yiv6881123364link-enhancr-element yiv6881123364link-enhancr-mobile-no-resize" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_75029" style="vertical-align:middle;font-size:9px;line-height:11px;color:#999999;">View on <span class="yiv6881123364link-enhancr-view-on-domain" style="font-weight:bold;">www.amrad.org</span></span></span></a></div></td><td colspan="1" rowspan="1" class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_75002" style="vertical-align:middle;width:100px;font-family:'Arial', 'Helvetica Neue', 'Helvetica', 'sans-serif';"><div class="yiv6881123364link-enhancr-element yiv6881123364link-enhancr-preview-wrapper" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_75001" style="max-width:100px;min-width:80px;overflow:hidden;text-align:right;line-height:11px;max-height:13px;font-size:0pt;"><span class="yiv6881123364link-enhancr-element yiv6881123364link-enhancr-preview-by yiv6881123364link-enhancr-mobile-no-resize" style="vertical-align:middle;font-size:9px;line-height:11px;color:#999999;">Preview by Yahoo</span></div></td></tr><tr id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74809"><td colspan="2" rowspan="1" class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74808" style="min-height:9px;background-color:#ffffff;font-size:0pt;border-collapse:collapse;"><div class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_74807" style="min-height:9px;background-color:#ffffff;font-size:9pt;"></div></td></tr><tr class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_75039"><td colspan="7" rowspan="1" class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_75038" style="min-height:1px;background-color:#e5e5e5;font-size:1px;border-collapse:collapse;"><div class="yiv6881123364link-enhancr-element" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_75037" style="min-height:1px;background-color:#e5e5e5;font-size:1px;line-height:0px;"> </div></td></tr></tbody></table></div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885"><br clear="none"></div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885">You will need:</div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885"><br clear="none"></div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885">(#1) One Amidon FT 37-75 toroid (available on eBay or directly from alltronics.com)</div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885">(#2) Several feet of 30 gauge, enamel coated or wire-wrap wire</div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885">(#3) A small plastic box (the input and output grounds cannot be connected, so you must use an insulated box)</div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885">(#4) Two chassis mounted RF connectors (I prefer BNCs)</div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885"><br clear="none"></div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885">Cost for one balun will be about $15 plus shipping and tax.</div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885"><br clear="none"></div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885">The AMRAD article says to wind 30 turns of the 30ga wire on opposite sides of the Amidon toroid, which is about 1/2" in diameter. The start and finish ends of each 30-turn winding go to separate RF connectors, making a very simple, ferrite-coupled transformer with a 1:1 turns ratio. 30ga wire will handle the 100mW output of the RPi but may not be good for more than a couple watts if you want to use it with another QRP transmitter.</div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885"><br clear="none"></div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885">I have the parts on mail order and will report on how well it works to eliminate the RPi sidebands.</div><div class="yiv6881123364yqt4852088237" id="yiv6881123364yqtfd27554"><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885"><br clear="none"></div><div dir="ltr" id="yiv6881123364yui_3_16_0_ym19_1_1473090208826_71885">Ron, W6XY</div></div></div></div></div><br><br></div> </div> </div> </div></div></body></html>