Paul Smedshammer wrote in
8.29:


We recently upgraded the avionics and instrument panel, which was a
great improvement. However, I'm having a problem transmitting under
high power. I get a crackly static (during transmittion only) when
over say 20" MP and 2500 RPM or 25" MP and 2200 RPM. At the start of
the attempted transmittion there is a lot of static and then if I hold
the transmit button down the static slowly dies away after about 5 to
10 seconds but the transmittion is still garbled (it is not sync'd
with the engine RPM - it is either there or it isn't). With less than
those power settings the transmittion is totally clear with no
crackling. All during my recent IFR training we never had the
problem, however, my instructor was good about taking it easy on the
engine and other than climbing we were always at 20" MP and 2400 RPM
or less power. I'm thinking we would have noticed the problem under
higher power settings and the problem would have been intermittent.


Problem solved! Thanks everybody who responded. After really trying
everything, I gave it one last try last night and took off. Same
problem. So, in an effort to try and figure it out, I was a little more
aggressive pushing in the radios trying to seat them deeper in their
trays. Well, nothing worked by just by chance my fingers hit the PMA6000
audio panel and the problem immediately went away! Taking my fingers
off, the problem came right back. It seems that even though the PMA6000
is seated all the way back in the tray and can't go any further (the
faceplate isn't touching the airframe it is only on the tray), it can
still move a little up and down in front. The higher power settings just
seem to cause a change in the vibration enough to cause the problem.
Just a very slight push with one finger on the front of the panel and the
problem goes away. Back on the ground I could replicate the problem by
pushing on the PMA faceplate softly and putting pressure up and down on
the faceplate. I will call PMA for suggestions on fixing or if it could
be something wrong in the unit.

This was a highly frustrating problem. We checked everything from the
battery to the engine mounts and everything in-between. It is so great
to finally find the problem and now we can fix it! Whew! Thanks again
everybody.

Paul Smedshammer