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sjhdcl(at)kingston.net
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 Posted: Wed Sep 06, 2006 2:35 am Post subject: Dual radio interference |
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I have 2 radios. GNS430 and GNC300XL.
Also have GMA340 audio panel and Approach Systems wiring harness.
Everything works great, I just have one annoyance. When I select both radio
to listen to and then transmit on one, the transmission is very garbled for
me. ATC reads me loud and clear but I can barely make out what I'm saying.
Happens with both radios.
Any ideas on how to fix this?
Steve
RV7A
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FLYaDIVE(at)aol.com
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| Posted: Wed Sep 06, 2006 4:17 am Post subject: Dual radio interference |
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In a message dated 9/6/06 7:52:05 AM Eastern Daylight Time,
sjhdcl(at)kingston.net writes:
| Quote: | I have 2 radios. GNS430 and GNC300XL.
Also have GMA340 audio panel and Approach Systems wiring harness.
Everything works great, I just have one annoyance. When I select both
radio
|
| Quote: | to listen to and then transmit on one, the transmission is very garbled for
me. ATC reads me loud and clear but I can barely make out what I'm saying.
Happens with both radios.
Any ideas on how to fix this?
Steve
RV7A
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Steve:
More than likely it is because of 'front end overload', a electronics term
for too much signal going into the Received radio.
There should be a pin hooked up that mutes the receive radio when the other
is transmitting. You will have to check on the schematic for the radios, the
audio panel and the Approach System.
Barry
"Chop'd Liver"
"Show them the first time, correct them the second time, kick them the third
time."
Yamashiada
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europa flugzeug fabrik
Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA
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| Posted: Thu Sep 07, 2006 2:13 pm Post subject: Re: Dual radio interference |
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| sjhdcl(at)kingston.net wrote: | | When I select both radio to listen to and then transmit on one, the transmission is very garbled for me. ATC reads me loud and clear but I can barely make out what I'm saying. Happens with both radios. |
How close are the 2 freqs on COM 1 and 2 when this phenomenon occurs? I couldn’t duplicate the phenomenon using two VHF handhelds, unless the freqs were really close together. That's also like the two devices are within inches of each other, not the case of an airplane antenna installation.
Fred F.
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sjhdcl(at)kingston.net
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| Posted: Fri Sep 08, 2006 3:05 am Post subject: Dual radio interference |
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Freqs are far apart. 122.5 and 126.7.
Antenna are about 4 ft apart.
Steve
RV7A
| Quote: | Time: 03:15:13 PM PST US
Subject: Re: Dual radio interference
From: "europa flugzeug fabrik" <n3eu(at)comcast.net>
<n3eu(at)comcast.net>
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| Quote: |
sjhdcl(at)kingston.net wrote:
> When I select both radio to listen to and then transmit on one, the
transmission
|
| Quote: | is very garbled for me. ATC reads me loud and clear but I can barely make
out what I'm saying. Happens with both radios.
How close are the 2 freqs on COM 1 and 2 when this phenomenon occurs? I
couldnt
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| Quote: | duplicate the phenomenon using two VHF handhelds, unless the freqs were
really
|
| Quote: | close together. That's also like the two devices are within inches of
each
|
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europa flugzeug fabrik
Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA
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| Posted: Fri Sep 08, 2006 10:13 am Post subject: Re: Dual radio interference |
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| sjhdcl(at)kingston.net wrote: | | Freqs are far apart. 122.5 and 126.7. |
4 MHz apart is huge. A fault in a COM to cause that is possible, but not the same fault on 2 radios within SuperLotto odds.
Is it just on one or both of those frequencies? Possibly also in a specific geographic area? If so, maybe there’s a TV broadcast tower which in combination with your xmit on the problem freq, is trashy signal being received on the selected freq of the other COM.
Otherwise, what’s common in the symptoms is when “BOTH” are selected. Per picture of a 340 audio panel, looks like “tactile” type switches, not pushbuttons. That means, if not mechanical relays, then semiconductor switches and a faulty component somewhere. However, this may be difficult to duplicate on an avionics bench.
So first I would pull the audio panel, and “hot wire” the system. It looks like we just need a “D”connector or two of opposite sex, bringing out 6 wires (mic audio, mic key, and phone audio each). Then, jury-rigged to your headset and mic or PTT setup, see if we still have the problem, which I presume occurs also on the ground. If not, it’s the audio panel, and not anything installed in the aircraft.
Fred F.
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