<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_1473372431013_63674"><b>Update</b>: I wound a second balun with 11.5 turns of #30 insulated wire and was more careful about the bifilar windings, starting both the primary and secondary at the same point on the Amidon toroid. In addition, I potted the wound toroid with common epoxy. The measured insertion loss decreased to 0.55dB at 14.1MHz. The signal looks great on the WSJT-X waterfall display, I don't see any sidebands and I'm not getting double spots now, even with a strong signal in the receiver.</div><div id="yui_3_16_0_ym19_1_1473372431013_63674"><br></div><div id="yui_3_16_0_ym19_1_1473372431013_63674">Ron, W6XY</div><div class="qtdSeparateBR"><br><br></div><div class="yahoo_quoted" id="yui_3_16_0_ym19_1_1473372431013_63678" style="display: block;"> <div style="font-family: times new roman, new york, times, serif; font-size: 16px;" id="yui_3_16_0_ym19_1_1473372431013_63677"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;" id="yui_3_16_0_ym19_1_1473372431013_63676"> <div dir="ltr" id="yui_3_16_0_ym19_1_1473372431013_63675"> <font size="2" face="Arial" id="yui_3_16_0_ym19_1_1473372431013_63941"> <br>----- Forwarded Message -----<br> <b><span style="font-weight:bold;">From:</span></b> Ron Ott <ronott@sbcglobal.net><br> <b id="yui_3_16_0_ym19_1_1473372431013_64081"><span style="font-weight: bold;" id="yui_3_16_0_ym19_1_1473372431013_64080">To:</span></b> TAPR HF Modes SIG Mailing List <hfsig@tapr.org> <br> <b><span style="font-weight: bold;">Sent:</span></b> Wednesday, September 7, 2016 7:14 PM<br> <b><span style="font-weight: bold;">Subject:</span></b> [hfsig] Sidebands on Raspberry Pi WSPR carrier - how much does a homebrew 1:1 balun help?<br> </font> </div> <div class="y_msg_container" id="yui_3_16_0_ym19_1_1473372431013_63839"><br><div id="yiv9836998307"><div id="yui_3_16_0_ym19_1_1473372431013_63838"><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_1473372431013_63837"><div id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12254"><br clear="none"></div><div id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><b id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12625">Construction</b><b id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12634">:</b> I received the parts to make a 1:1 balun this afternoon and wound 5 turns each of #30 insulated wire for the primary and secondary on an Amidon FT 37-75 toroid core. The primary and secondary windings are bifilar wound (interleaved) around the toroid with leads coming from opposite sides of the "O". The balun is installed in a small plastic box with BNC connectors on each end, no potting or glue was used.</div><div id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><br clear="none"></div><div dir="ltr" id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><b id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12626">Insertion loss:</b> I measured 1dB loss at 14MHz when the balun was inserted in a coaxial line from my HP signal generator and terminated in 50ohms; with some experimentation, this loss could probably be reduced as I just guessed at the number of turns based on the AMRAD design for a LF balun. As a result, my ERP will decrease from 18dBm to 17dBm.</div><div dir="ltr" id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><br clear="none"></div><div dir="ltr" id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><b id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12635">Effect on sidebands due to AC modulation: </b> Listening to myself on the air on 20m while transmitting with the Raspberry Pi, I still get occasional double spots due to a sideband 120Hz from the carrier frequency. However, the difference betwen the carrier and sideband signal strengths can be over 50 dB with the balun, according to WSJT-X, making the RPi WSPR transmitter apparently within FCC specs for spurious transmissions.</div><div dir="ltr" id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><br clear="none"></div><div dir="ltr" id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253">Looks like this is a worthwhile addition to the RPi TAPR kit setup and helps reduce the sidebands 10s of dB, at least at my station.</div><div dir="ltr" id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><br clear="none"></div><div dir="ltr" id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253">73, Ron</div><div class="yiv9836998307yqt7702941505" id="yiv9836998307yqtfd61629"><div dir="ltr" id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><br clear="none"></div><div dir="ltr" id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><br clear="none"></div><div id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><br clear="none"></div><div id="yiv9836998307yui_3_16_0_ym19_1_1473298633268_12253"><br clear="none"></div></div></div></div></div><br><div class="yqt7702941505" id="yqtfd13182">_______________________________________________<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_1473372431013_64082">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_1473372431013_64083">http://www.tapr.org/mailman/listinfo/hfsig</a><br clear="none"></div><br><br></div> </div> </div> </div></div></body></html>