tag:blogger.com,1999:blog-7590176649168185428.post2487916078419270110..comments2024-03-28T18:51:21.655-04:00Comments on SolderSmoke Daily News: Direct Conversion Receivers, AF Transformers, and MotorboatingBill Mearahttp://www.blogger.com/profile/07662500663603350847noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-7590176649168185428.post-15221745097731067042014-03-12T21:34:05.213-04:002014-03-12T21:34:05.213-04:00In addition to Michael's comments on the trans...In addition to Michael's comments on the transformer radiating, look at the power supply bus filtering and at the capacitor locations. The bus may soft or it may not be filtered close enough to the transformer and output transistor. As for shielding, you could be inducing currents into your ground plane so don't overlook that possible path.<br /><br />I can get some transformer lamination steel if you want to try to make a shield. Look for an email from me on this topic.David Wilsonhttps://www.blogger.com/profile/04861462976116484794noreply@blogger.comtag:blogger.com,1999:blog-7590176649168185428.post-14453954854401723352014-03-12T14:17:54.143-04:002014-03-12T14:17:54.143-04:00Except it changes with the volume control, I'd...Except it changes with the volume control, I'd wonder if it's audio feedback around the mixer transistor.<br /><br />The RC circuit wouldn't radiate, but the AF transformer might inductively couple to the antenna, thus providing a feedback path.<br /><br />I once played with an inductive loop around my room, feeding it with an audio amplifier. I could pick up the signal with an amplifier and inductive pickup, but if I turned up the amplifier feeding the loop, I'd get oscillation.<br /><br />What seemed to be happening was the loop signal was getting into my turntable cartridge, thus providing a feedback loop.<br /><br />It is somewhat possible the af transformer is doing the same.<br /> <br /> Michael VE2BVW<br />Michael Blacknoreply@blogger.com