Chuck N4AVC's use of the frequency counter in his digital multimeter is pretty cool and innovative. And it is nice to have yet another receiver in Virginia; he is down in the Richmond area. And of course the Sharpie callsign tattoos on the wooden board are really nice.
Chuck writes:
Completed!!! For Pete: "She ain't pretty, but she sure can cook!". Thanks Bill and Dean, I enjoyed the build and testing. It's funny, the audio oscillates on an older 9v battery, but is clean on the 9.5v bench supply. Going to put Bill's mod on the inductor to make tuning a little finer and spread the boards out a little more. I used the double sided boards I had and there is some interaction between the boards.
Congratulations Chuck! Welcome to the Hall of Fame!
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Old 9V Batteries tend to have higher internal resistance. Your bench supply may have low internal resistance. DCR's have very high audio gain, and a feedback path is possible on the +9.5V line. So, check those 47uF caps (C10,C15) and see if you have the right values. It wouldn't hurt to add a couple more on that line to ground. More effectively, break the line between C15 and R8 (refer to schematic), and insert a 220~470 ohm resistor.
ReplyDeleteBut Beware!! Unauthorized Mods will revoke your highly prized Soldersmoke Hall of Fame Status! You don't want that to happen! ---So just put in a fresh 9V battery and call it a day.