WLawless at analogic.com
Thu Mar 9 13:05:50 EST 2000
I've encountered hum twice with 2 DVKs: MFJ-432 & recently MFJ-434.
MFJ-432 was a ground loop through the 12v supply line from an Astron supply feeding rig (IC-706 MK2) and MFJ-432. Solved by using a plug-in-the-wall AC/DC adapter to power DVK.
Recent hum was lack of ground on MFJ-434, which has a ground terminal (screw with wing nut). Grounding solved problem. FYI - I was using both MFJ-432 & MFJ-434 in series... both worked OK.
Makes me wonder if MFJ-432 couldn't perhaps benefit from an earth ground to its chassis??
1. Run DVKs off the internal back-up battery... if no hum, you know its power supply related.
2. Record message with no connections other than microphone. Play through radio & listen.
3. Compare using the built-in mic; if no hum this way but hum with tip #2, then it's in mic.
4. Simplify connections and nibble away.
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