On Tue, 07 Nov 2006 23:36:44 GMT, ml wrote:
: In article , ml
: wrote:
:
: hi
:
: was hoping that someone might be able to share some advice
:
: rig MVField mic stock vs Heil w/heil cable (goldline 5)
:
: when i tx there is a slight but clearly noticable humm like a 60cycle
: sounds a little like the buzz of a transformer my tube stereo would do
: that if i touched a speaker wire w/o gnd
:
:
: here is what i observed:
:
: if i unscrew the mic plug at rig and pull it out a little so the mic
: metal connector dosn't touch the rig (leaving enough for pins to
: contact) humm goes away
:
: if i use the stock mic or another yaesu mic no humm not a drop
:
: if i use my astron to power the rig instead of it's built in supply the
: humm goes away
:
: both the rig and the mic etc are all kind of new moving the heil cable
: or mic location hum is same
:
:
: i tried removing and adding ground wires to the chassy gnd screw no
: change (thou my coax shields are grounded )
:
:
: my guess is the rig and it's connections are 'ok' since the stock
: mic's don't have any problems
:
: so guessing the problem is isolated between the heil cable/mic but i
: dunno somthing is not right and i know it's prob simple
:
: what is the likely cauze of the hum? whats the best test and or fix??
:
:
:
:
: any help is appreciated

It sounds very much like an induction ground loop. When you remove
the outer connector, you are probably breaking a current loop that
nearby 60 Hz magnetic fields are inducing. The problem mic must
somehow allow small induced currents to flow through its cable, and
you need to put a stop to them somehow. I'd start checking the mic
for failed components since your other mics work just fine. Maybe the
mic impedance is mismatched. Hard to tell at this distance, but in
that case an impedance matching device would probably help you.