<html><head></head><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:16px"><div dir="ltr" id="yui_3_16_0_ym19_1_1473090208826_87663"><span id="yui_3_16_0_ym19_1_1473090208826_87664">Hi Tom -- I agree that 30 turns is probably too much inductance at 14MHz. When you say bifilar, do you mean simply interleave the two windings round the toroid? Looking at baluns made by Balun Designs, I see only a handful of turns at HF - of course this depends on the ferrite too. So, how about:</span></div><div dir="ltr" id="yui_3_16_0_ym19_1_1473090208826_87663"><span><br></span></div><div dir="ltr" id="yui_3_16_0_ym19_1_1473090208826_87663"><span id="yui_3_16_0_ym19_1_1473090208826_87880">* 5 turns each of 20 or 22 ga enamelled wire for the primary and secondary windings</span></div><div dir="ltr" id="yui_3_16_0_ym19_1_1473090208826_87663"><span id="yui_3_16_0_ym19_1_1473090208826_87906">* Interleave the primary and seconday windings</span></div><div dir="ltr" id="yui_3_16_0_ym19_1_1473090208826_87663"><span id="yui_3_16_0_ym19_1_1473090208826_87921">* Amidon FT 37-75 core</span></div><div dir="ltr" id="yui_3_16_0_ym19_1_1473090208826_87663"><span><br></span></div><div dir="ltr" id="yui_3_16_0_ym19_1_1473090208826_87663"><span>Ron/W6XY</span></div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1473090208826_87666"><br><br></div><div class="yahoo_quoted" id="yui_3_16_0_ym19_1_1473090208826_87740" 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_87739"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;" id="yui_3_16_0_ym19_1_1473090208826_87738"> <div dir="ltr" id="yui_3_16_0_ym19_1_1473090208826_87737"> <font size="2" face="Arial" id="yui_3_16_0_ym19_1_1473090208826_87736"> <hr size="1" id="yui_3_16_0_ym19_1_1473090208826_87735"> <b><span style="font-weight:bold;">From:</span></b> Tom McDermott <tom.n5eg@gmail.com><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 11:55 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_87759"><br><div id="yiv0476064323"><div id="yui_3_16_0_ym19_1_1473090208826_87758"><div dir="ltr" id="yui_3_16_0_ym19_1_1473090208826_87757"><div id="yui_3_16_0_ym19_1_1473090208826_87756"><div id="yui_3_16_0_ym19_1_1473090208826_87755"><div id="yui_3_16_0_ym19_1_1473090208826_87754"><div id="yui_3_16_0_ym19_1_1473090208826_87753"><div id="yui_3_16_0_ym19_1_1473090208826_87752">Hi Ron, thanks for the pointer.<br clear="none"><br clear="none">For use at 14 MHz, winding the two transformer windings on opposite sides of the ferrite core<br clear="none"></div>could be an issue. That causes a lot of leakage inductance, and at 14 Mhz, depending on load<br clear="none">Z may attenuate the desired signal. 30 turns might be a bit much at 20 meters<br clear="none"><br clear="none">Forming a bifilar twisted pair of the two windings reduces the leakage inductance a lot.<br clear="none"></div></div><div id="yui_3_16_0_ym19_1_1473090208826_87797"><br clear="none"></div>Minimizing the interwinding capacitance would not seem to be much of a consideration<br clear="none">at 60 or 120 Hertz.<br clear="none"></div><br clear="none"></div>-- Tom, N5EG<div class="yiv0476064323yqt1989226882" id="yiv0476064323yqtfd38890"><br clear="none"><br clear="none"><br clear="none"><div id="yui_3_16_0_ym19_1_1473090208826_87799"><div id="yui_3_16_0_ym19_1_1473090208826_87798"><br clear="none"></div></div></div></div></div></div><br><div class="yqt1989226882" id="yqtfd75931">_______________________________________________<br clear="none">hfsig mailing list<br clear="none"><a shape="rect" ymailto="mailto:hfsig@tapr.org" href="mailto:hfsig@tapr.org" id="yui_3_16_0_ym19_1_1473090208826_87944">hfsig@tapr.org</a><br clear="none"><a shape="rect" href="http://www.tapr.org/mailman/listinfo/hfsig" target="_blank" id="yui_3_16_0_ym19_1_1473090208826_87945">http://www.tapr.org/mailman/listinfo/hfsig</a><br clear="none"></div><br><br></div> </div> </div> </div></div></body></html>