No way the sensitivity difference between the two radios should be 20 dB --
that reflects an incident signal strength difference of 100-fold! If the
Garmin is not defective (and the unit swap seems to confirm this) then the
receive signal is being attenuated by roughly 20 dB someplace. This should
be fairly easy to find using a spectrum analyzer or similar instrument,
again something any avionics shop should have available.

However, I must wonder why your avionics shop isn't going through these
rather obvious diagnostic steps without outside help.


-Elliott Drucker