{"id":5945,"date":"2013-10-19T12:16:00","date_gmt":"2013-10-19T01:16:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2013\/10\/19\/bitx-build-update-14-stability\/"},"modified":"2025-07-21T19:53:06","modified_gmt":"2025-07-21T09:53:06","slug":"bitx-build-update-14-stability","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2013\/10\/19\/bitx-build-update-14-stability\/","title":{"rendered":"BITX Build Update #14 — STABILITY!"},"content":{"rendered":"
<\/a><\/div>\n

Good news on the BITX. I think I have solved the low frequency oscillation problem in the power amplifier. I tried running the PA off a separate power supply — the oscillations disappeared leading me to conclude that the feedback was taking place via the power supply lines. I put a 22 uF cap to ground from the top of the PA’s RF choke. With this cap in place I can dispense with the separate supply kludge. The amp is stable. <\/strong>
<\/strong>
This morning I also resolved a different stability problem. I’m using a relay for T\/R switching. One set of contacts controls the DC power, the other set was supposed to disconnect the receiver input from the antenna\/lowpass filter when on receive. But I had positioned the relay too far from the LP filter and RX input, so I ended up with this long piece of coax that was hanging off the PA output terminal and carrying lots of RF on transmit. Yes, this led to oscillations. I thought about repositioning the relay, but I think part of the problem is that even if optimally positioned, the long unshielded contact levers inside this relay would be radiating a lot of RF and causing stability problems. So instead I put a small reed relay very close to the PA out and RX in connections. It carries the signal to the receiver when in R mode, and disconnects the RX when in T mode, without any long coax lines or unshielded relay levers. It works. <\/strong>
<\/strong>
I still have a few things to do: <\/strong>
— I need to build a proper speaker amplifier so that I can dispense with the amplified computer speakers KLUDGE. <\/strong>
— I need to get a 3 pole double throw switch and some crystal sockets so that I can switch crystals from the front panel. Three rocks will cover all of 17 meter phone. <\/strong>
— I have to build a case for this rig. I’m thinking wood, with tin or aluminum sheeting glued to the inside (for shielding). <\/strong><\/p>\n

Our book: “SolderSmoke — Global Adventures in Wireless Electronics” http:\/\/soldersmoke.com\/book.htm<\/a> Our coffee mugs, T-Shirts, bumper stickers: http:\/\/www.cafepress.com\/SolderSmoke<\/a> Our Book Store: http:\/\/astore.amazon.com\/contracross-20<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Good news on the BITX. I think I have solved the low frequency oscillation problem in the power amplifier. I tried running the PA off a separate power supply — the oscillations disappeared leading me to conclude that the feedback was taking place via the power supply lines. I put a 22 uF cap to … Continue reading “BITX Build Update #14 — STABILITY!”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":5946,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[28,25],"tags":[],"class_list":["post-5945","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-bitx20","category-troubleshooting"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/5945","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/comments?post=5945"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/5945\/revisions"}],"predecessor-version":[{"id":5947,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/5945\/revisions\/5947"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media\/5946"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=5945"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=5945"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=5945"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}