Today's Message Index:
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1. 12:41 AM - VHF Transmitting Noise (Garlick, Bill (W.D.))
2. 08:08 AM - Re: VHF Transmitting Noise (Noel Loveys)
Message 1
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| Subject: | VHF Transmitting Noise |
Hi
I'd appreciate some comments or advice from avionics installers who
half-understand what they're doing? (My limits are that I need to follow
manufacturers' installation instructions and wiring diagrams to the
letter; and if something doesn't quite work I'm at a complete
loss!...Although if any advice was something like connecting a xxx ohm
resistor in parallel in a particular circuit, I could manage to cope
with that).
I have just installed an ICOM IC-A200 transceiver coupled with a PS
Engineering PM501 Intercom in a newly built Vans RV7, and when I press
the PTT switch I get a lot of noise feeding-back into the earphones as
I'm talking... The Air Traffic Controllers say they're reading me
"fives", and the noise doesn't occur when Receiving or when using the
voice-activated intercom. The noise isn't in time with the engine, but
is constant whilst transmitting and sounds like wind blowing across the
microphone.
Any ideas about what could be wrong?
Thanks
BillG
Message 2
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| Subject: | VHF Transmitting Noise |
What you have described sounds a lot like alternator whine coming into your
audio panel. If it is, you should be able to remove it by installing a
choke in the power line to your PN501. A choke is simply a coil and a
capacitor, in parallel, tuned to remove alternator frequency sound. It is
wired in series in the B+ line of your audio panel and it stops the noise
which is coming in on that wire. Where to get the choke depends on the
registration of your plane GA will have to get it from an avionics shop,
others, from an electronics or amateur radio outlet. A lot of AB owners
can get a lot of free help from local amateur radio ops. They really know
what they are doing form a practical point.
Also check the wires between your transceiver and audio panel have the
shield grounded only at one end.
The last piece of advice is the one that is a pain... When you get your
system working draw up a little block interconnect diagram of exactly what
you have there so if you have future problems you will have an idea where to
look. You can start on that interconnect diagram ASAP even before installing
a choke. Better avionics shops won't put a finger on an installation until
they have finished their interconnect diagram. Doing that makes for less
mistakes in installation and much less problems. Things to include in the
interconnect diagram are wire connecters and fuse locations.
Hope this helps
Noel
From: owner-avionics-list-server@matronics.com
[mailto:owner-avionics-list-server@matronics.com] On Behalf Of Garlick, Bill
(W.D.)
Sent: Tuesday, January 15, 2008 5:10 AM
Subject: Avionics-List: VHF Transmitting Noise
Hi
I'd appreciate some comments or advice from avionics installers who
half-understand what they're doing? (My limits are that I need to follow
manufacturers' installation instructions and wiring diagrams to the letter;
and if something doesn't quite work I'm at a complete loss!...Although if
any advice was something like connecting a xxx ohm resistor in parallel in a
particular circuit, I could manage to cope with that).
I have just installed an ICOM IC-A200 transceiver coupled with a PS
Engineering PM501 Intercom in a newly built Vans RV7, and when I press the
PTT switch I get a lot of noise feeding-back into the earphones as I'm
talking. The Air Traffic Controllers say they're reading me "fives", and the
noise doesn't occur when Receiving or when using the voice-activated
intercom. The noise isn't in time with the engine, but is constant whilst
transmitting and sounds like wind blowing across the microphone.
Any ideas about what could be wrong?
Thanks
BillG
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