Follow up on Microair distortion

In 2004 there was a discussion of the fact that some glider radios
were very distorted when being received by the Microair 760. At that
time I suspected that off frequency transmitters, combined with the a
narrow IF passband of the Microair were causing the problem. I no
longer think this is true.

It always struck me as significant that no FAA radio station was ever
distorted when received by the MIcroair but several glider radios of
much lower power output were distorted even when distant from the
receiver. Clearly receiver overloading was not the cause of the
problem. Experiments with zero beating transmitters against a
frequency standard did not show any significant frequency offsets.

I recently had the time to do some more testing with the owner of the
source of one the most distorted transmissions. It turned out the
problem was severe overmodulation of the transmitter. The simple
short term fix was to change to a different microphone.

In this recent test, while the transmission was intelligible on
another receiver, the audio quality was significantly improved on that
receiver when the microphone was changed.

It appears that the Microair may be more sensitive to overmodulated
signals than other receivers but the solution is the same. Get the
owners of the offending radios to reduce their modulation level by a
reduction in mic gain, changing the microphone type, or maybe just by
not shouting into the microphone.

Andy