[aprssig] Mic muting

[Scott Miller]

I very rarely work with mic encoder mode, and I just wired up a TM-271A for
some testing yesterday.  It worked fine, but I noticed that the mic audio
isn't muted when the PTT is released.  If there's too much background noise
it mangles the packet data.

I haven't seen any tracker circuits with a provision to handle mic muting,
but I don't have a TAPR Mic-E schematic available either.  Was it able to
mute the mic?  Or is it not a problem with most radios?  Most of my testing
in the past has been with radios like the Kenwood TK-90, where there's a
separate accessory connector and the mic is muted when the auxiliary PTT is
used.

Scott
N1VG