nuckolls.bob(at)aeroelect
Guest
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 Posted: Wed Oct 30, 2013 6:02 pm Post subject: Transponder Interference with Icom A-22 Comm Radio |
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At 11:28 AM 10/29/2013, you wrote:
I just installed a Sandia Transponder with an Icom A-22 handheld
radio hard wired into the electrical system. On the first flight,
ATC had a difficult time understanding me and I heard "clicks" in
then headset while receiving. Not knowing if it was RF interference
from the transponder OR feedback from the aircraft 12 volt power
system, I removed the hard wire power from the radio and used the
battery pack... Everything worked great.
Radios of this variety are never qualified to DO160
recommendations for immunity to noise common to
the vehicular dc bus. The exact nature of
ATC's complaint would be good. The 'clicking'
you describe is not particularly interesting.
Further, the noise heard on your transmitted
signal may be very different than anything
you hear on receive.
Is this test with engine running or not? Does
it go away with the alternator off? Could you
record a sample of the noise received by
your listeners. Got access to a pocket recorder
and second transceiver to run an experiment.
Have somebody talk to you on the compromised
radio so you can offer an interpretation of
what you hear.
I even placed the VHF receiver within a inch of the transponder
antenna while it was being interrogated and it still worked fine.
Since the complaint was against your transmitted
signal, the experiment may not have any
significance.
Seems I am having some strange pulses running through the 12V system
while the transponder is ON because it is eliminated when I remove
acft power from it and use the battery pack.
Check your transmitted signal with the
radio hookd to the airplane with the
transponder on/off, alternator on/of
and any other electro-whizzies.
QUESTION - Is there something I can do or install that will isolate
electrically the Comm Radio from getting this feedback
from the transponder OR is thernee something I can add to the
Transponder Power feed?
Not enough data for a specific suggestion.
A simple noise filter may do the job but
it would help to know exactly where the
noise is coming from.
Bob . . .
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