<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_1473298633268_12254"><br></div><div id="yui_3_16_0_ym19_1_1473298633268_12253"><b id="yui_3_16_0_ym19_1_1473298633268_12625">Construction</b><b id="yui_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="yui_3_16_0_ym19_1_1473298633268_12253"><br></div><div id="yui_3_16_0_ym19_1_1473298633268_12253" dir="ltr"><b id="yui_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 id="yui_3_16_0_ym19_1_1473298633268_12253" dir="ltr"><br></div><div id="yui_3_16_0_ym19_1_1473298633268_12253" dir="ltr"><b id="yui_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 id="yui_3_16_0_ym19_1_1473298633268_12253" dir="ltr"><br></div><div id="yui_3_16_0_ym19_1_1473298633268_12253" dir="ltr">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 id="yui_3_16_0_ym19_1_1473298633268_12253" dir="ltr"><br></div><div id="yui_3_16_0_ym19_1_1473298633268_12253" dir="ltr">73, Ron</div><div id="yui_3_16_0_ym19_1_1473298633268_12253" dir="ltr"><br></div><div id="yui_3_16_0_ym19_1_1473298633268_12253" dir="ltr"><br></div><div id="yui_3_16_0_ym19_1_1473298633268_12253"><br></div><div id="yui_3_16_0_ym19_1_1473298633268_12253"><br></div></div></body></html>