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

so the fix for mircroair is for everyone else to change their
equipment? sounds odd.
Chris

actually far from it...there have been several modifications and updates to
the Microair radios and a lot of improvements since the original
manufacturer first introduced these radios...early ones were IMHO real bad
radios...but the most recent versions and updates have all been improvements
and in fat the current M760 Ver Q is really an excellent and completely
different radio inside and out from all previous versions.keep in mind also
that the company changed hands quite some time ago and from the beginning
has been sorting out the original manufactures poor design work.
I still find most problems with Microair radios even with most early
versions is user/installer errors and just plain bad installation, next is
like with nearly all transceivers bad power supplies either bad batteries,
bad battery charging or insufficient cabling and bad soldering.This is not
to say that these and all other avionics cannot be at fault but most common
is as I have described.
tim
Please visit the Wings & Wheels website at www.wingsandwheels.com


"chris ruf" wrote in message
...
so the fix for mircroair is for everyone else to change their
equipment? sounds odd.
Chris

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Just to weigh in. I have an earlier Microaire M760 from 2004 or
2005. At first it worked great. Then I had an issue with distortion
in my transmit. I returned it to Eire Aviation (http://
www.erieaviation.com/radio.htm) in 2007 for some mods. Things got a
little better. I then hear about some other mods and sent it back to
Eire again and since then my radio have been perfect. I have been
told that the mods had to do with loose or bad grounds that either 1)
happen over time or 2) we related to "bad" designs.

The point of all this is the Microaire has been updating their design
quite often and providing those updates to their dealers. This is all
for the good. Also, Eire Aviation has been great working with. Quick
and professional.

My $0.02.

- John DeRosa