Barry, G4RKO wrote:
My MH-2 mic is very intermittent when the PTT is pressed. Sometimes it works
fine and allows me to transmit, other times it does nothing - no transmitted
signal. The mic in itself works very well and I get excellent audio reports
especially if I pull the transmit line down by keying my morse key in SSB
mode whilst transmitting into the MH-2 mic. I have stripped the Heil mic
down and can find no evidence of poor or partial connections or the dreaded
dry joints. Is this a common problem with this mic or should I be looking
elsewhere for the cause? Any suggestions most welcome.
=========================
General experience from many years servicing radios on ships with curly-cord
mics on the bridge-to-bridge VHF radios is that the failure most often
occurs in the cord itself, Barry.
I believe the MH-2 uses such a cord.
One of the wires inside the cord breaks *inside* the insulation, so the cord
looks fine. Even if you were to strip the outer cover, the wires inside
would probably look normal. But inside one of those wires the copper
conductors have crystallized from movement and pulled apart, so they only
touch when the cord is in a certain position with, or without a certain
strain on it. It varies a great deal.
In this case, it sounds like the 'hot' PTT line has broken and become
intermittent.
I agree with you - the first thing I always did in such cases was to check
the ptt switch - especially on a ship where salt air can corrode contacts,
but the failure was usually in the cord.
You can try isolating it by holding down the PTT and wiggling the cord, but
all that might do is confirm that the cord is bad. They aren't worth trying
to repair. You can't open the outer casing in a way that is easy to put
right again unless it happens to be right at the end. Perhaps a better way
to confirm the problem is in the cord is to temporarily connect another
conductor between the mic and the jack, outside the cord and in parallel
with the PTT line. If the intermittent goes away, you've confirmed a bad
cord.
On the plus side, those cords are pretty easy to find.
Ron AC7AC
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