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A200 and Flightcom squeal

 
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nuckolls.bob(at)aeroelect
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PostPosted: Mon Nov 12, 2012 6:38 am    Post subject: A200 and Flightcom squeal Reply with quote

Quote:


It's would be great to hear some feedback from the pro Bob Nuckolls.

When you can "make a difference" with the waving of hands,
two possibilities pop up (there may be more but I'm on my
first cup of coffee). The first suggests an acoustic
coupling wherein the microphone is hearing audio leakage
from under your headset seals . . . seems unlikely due
to the noise cancelling designs for most aviation
mic-headsets and the effectiveness of the seals. But
I wouldn't throw that one out yet.

The other is an RF interference condition. Hi levels
of RF in the cockpit and in PARTICULAR from an AM
transmitter (easily de-modulated by non-linearities
in over-stressed circuitry) can 'paint' electronics
with a stress they were never designed to withstand.

Try putting a dummy load on the A200 antenna connector
and see if noise goes away. Here's a DIY load you can
build if you can't put your hands on one by some other
means.

http://tinyurl.com/cchp3pf

If the noise goes away, then inspection of the
antenna system is indicated. Do an SWR check on the
A200 antenna, alternatively you can move the dummy
load to the far end of the coax and see if the noise
is still gone. The most common sources of hi level
cockpit radiation are the byproduct of either antenna
proximity combined with low coupling losses (plastic
airplane) -OR- bad feedline where the #1 culprit in
my experience was a shield termination pulling out
of the clamp on a old nut-style UG-88 connector.

A a-placing-of-hands-healing by grabbing the mic boom
suggests that demodulation of the AM transmitter signal
is taking place in the electronics that conditions
the signal from modern electret microphone cartridges
to emulate the legacy aviation carbon microphone.
(A(at)$%!#(at)$%!! why is it that the rest of the world
talks to each other on digital spread spectrum, or FM
supported by electronics having no vestige of WWII
technologies . . . while aviation still struggles
with these system integration alligators? A topic
for another time).
Bob . . .


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SIDESLIP



Joined: 14 Oct 2012
Posts: 78
Location: CYOO

PostPosted: Mon Nov 12, 2012 8:42 am    Post subject: Re: A200 and Flightcom squeal Reply with quote

Bob....

Thanks for the input. The audio leakage from the headsets is, in my opinion almost impossible, stricktly due to the fact they fit so well, and are nicely broken in. The other part that super confuses me is that the handheld is wired into the system exactly the same as the A200, with the only variable being a different antenna.

So, you can see how it points me to the A200's settings of mic gain/sidetone and or antenna issues. I've been told to try and simply swap the antenna connections and try this first.

Make sense? I "think" I have an SWR meter still from my CB radio days around somewhere.... I believe. I'll look later tonight. Bob, what does your gut tell you about this? Antenna? Simple adjustments? I know that when we turned the sidetone down to factory settings, the squeal was nowhere near as bad, but still no clear transmission. Just less invasive. When I pulled the mic jack mid transmit, the squeal disappeared immediately.

Chad


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SIDESLIP



Joined: 14 Oct 2012
Posts: 78
Location: CYOO

PostPosted: Mon Nov 19, 2012 5:24 pm    Post subject: Re: A200 and Flightcom squeal Reply with quote

Swapped antennas. Just changed the connections at the antennas, and was able to transmit from the apron to an in flight aircraft over 25miles away! The twiggy looking coat hanger style antenna under the fuselage works like a charm! The handheld works fine on the antenna that the A200 didn't like. Still need to flight test the final result, but all appears resolved....... Go figure!

Chad


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PostPosted: Wed Nov 21, 2012 7:34 am    Post subject: A200 and Flightcom squeal Reply with quote

At 07:24 PM 11/19/2012, you wrote:
Quote:


Swapped antennas. Just changed the connections at the antennas, and
was able to transmit from the apron to an in flight aircraft over
25miles away! The twiggy looking coat hanger style antenna under the
fuselage works like a charm! The handheld works fine on the antenna
that the A200 didn't like. Still need to flight test the final
result, but all appears resolved....... Go figure!

If I understand correctly, the coax feed lines to the
two antennas are long enough and the antennas are
close enough to each other that you could simply swapped
the feed lines?

Refresh my memory . . . what kind of airplane, what
kind of antennas and where are they located on the
airplane?

Did you ever get a look-see at SWR for the 'problem'
antenna?
Bob . . .


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SIDESLIP



Joined: 14 Oct 2012
Posts: 78
Location: CYOO

PostPosted: Wed Nov 21, 2012 3:29 pm    Post subject: Re: A200 and Flightcom squeal Reply with quote

Bob;

It's a Zodiac 601XL-B. One antenna is right behind pilots head, other right below. The coax is long enough on each to swap connections AT the antennas. I never got a look at the SWR for the antennas. I can't believe the range I get now. 20 miles from sitting on the apron at the airport talking to an aircraft flying THAT far away! Unreal! With an antenna UNDER the airframe none the less! Did some taxi tests today, and tower was very happy with my clarity etc. 5/5. The handheld also works on the problem antenna with no issues. My theory....... The A200 puts out just a little too much power to be so close to the actual pilots head. Within 2 feet of headset. When I moved my head forward, the squeal almost completely disappeared.

Puzzled...... But happy with result.

Chad


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PostPosted: Wed Nov 21, 2012 5:15 pm    Post subject: A200 and Flightcom squeal Reply with quote

The A200 puts out just a little too much power to be so close to the
actual pilots head. Within 2 feet of headset. When I moved my head
forward, the squeal almost completely disappeared.

Puzzled.....

I'm not. The electret microphone in your
mic-headset has some electromagic devices
between the actual mic cartridge and the
radio . . . seems our radios would STILL
work fine with a 1940's carbon microphone
connected to them.

That little bit of electronics has to
amplify MICROVOLTS off the microphone up
to several hundreds of millivolts to make
the transmitter happy. What's more, the
electronics is fitted with some rather
efficient antennas on both the goesinta
and goesouta connections. I wish I'd
known that your headset was so exposed to
the antenna . . . that would have raised a
big red flag.

Bob . . .


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SIDESLIP



Joined: 14 Oct 2012
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Location: CYOO

PostPosted: Wed Nov 21, 2012 6:26 pm    Post subject: Re: A200 and Flightcom squeal Reply with quote

Bob;

So then this makes sense to you? Why doesn't the handheld not show similar issues with that same antenna behind my head? Lower output? Less of a radio over all? So in the end, it very well could have been the close proximity of the antenna for the A200?

Chad


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Kellym



Joined: 10 Jan 2006
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PostPosted: Wed Nov 21, 2012 6:31 pm    Post subject: A200 and Flightcom squeal Reply with quote

Not Bob,
But yes. 5-8 watts of output very close to headset, vs 150 milliwatt
output of handheld.
I've seen similar effects when headset was close to antenna coax and
coax had bad shield connection.
Kelly
On 11/21/2012 7:26 PM, SIDESLIP wrote:
Quote:


Bob;

So then this makes sense to you? Why doesn't the handheld not show similar issues with that same antenna behind my head? Lower output? Less of a radio over all? So in the end, it very well could have been the close proximity of the antenna for the A200?

Chad

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C-GYXQ. 912ULS. 601XL-B


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PostPosted: Wed Nov 21, 2012 10:24 pm    Post subject: A200 and Flightcom squeal Reply with quote

At 08:30 PM 11/21/2012, you wrote:
Quote:


Not Bob,
But yes. 5-8 watts of output very close to headset, vs 150 milliwatt
output of handheld.
I've seen similar effects when headset was close to antenna coax and
coax had bad shield connection.

Agreed. The few times I've encountered high levels
of RF in the cockpit, it proved to be a shield pulled
out of the clamp in an old style BNC connector with
a clamp-nut. This turned the coax into a long-wire
antenna that radiated the interior of the airplane.

In your case, the antenna was for all practical
purposes in the cockpit and no doubt both antenna
and feed line were functioning as advertised.

Bob . . .


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uuccio(at)gmail.com
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PostPosted: Wed Nov 21, 2012 11:29 pm    Post subject: A200 and Flightcom squeal Reply with quote

So I'm wondering: my Nav antenna is a dipole type which i plan to locate right above my head stretching from one side of the cockpit to the other (in the same plane as the wing). So it will be only a foot or two from the headsets. Is this a bad idea?

Sacha
Kitfox IV
On 22/nov/2012, at 02:14, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

Quote:




The A200 puts out just a little too much power to be so close to the actual pilots head. Within 2 feet of headset. When I moved my head forward, the squeal almost completely disappeared.

Puzzled.....

I'm not. The electret microphone in your
mic-headset has some electromagic devices
between the actual mic cartridge and the
radio . . . seems our radios would STILL
work fine with a 1940's carbon microphone
connected to them.

That little bit of electronics has to
amplify MICROVOLTS off the microphone up
to several hundreds of millivolts to make
the transmitter happy. What's more, the
electronics is fitted with some rather
efficient antennas on both the goesinta
and goesouta connections. I wish I'd
known that your headset was so exposed to
the antenna . . . that would have raised a
big red flag.

Bob . . .







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nuckolls.bob(at)aeroelect
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PostPosted: Thu Nov 22, 2012 6:11 am    Post subject: A200 and Flightcom squeal Reply with quote

At 01:28 AM 11/22/2012, you wrote:
Quote:


So I'm wondering: my Nav antenna is a dipole type which i plan to
locate right above my head stretching from one side of the cockpit
to the other (in the same plane as the wing). So it will be only a
foot or two from the headsets. Is this a bad idea?

Sacha
Kitfox IV

Receiving antennas do not radiate,
only transmit antennas: VHF Comm and Transponder

Bob . . .


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uuccio(at)gmail.com
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PostPosted: Thu Nov 22, 2012 9:43 am    Post subject: A200 and Flightcom squeal Reply with quote

Doh! Smile thank you.... I need to put "turn brain on before asking question" on my checklist Smile

On 22/nov/2012, at 15:10, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

Quote:


At 01:28 AM 11/22/2012, you wrote:
>
>
> So I'm wondering: my Nav antenna is a dipole type which i plan to locate right above my head stretching from one side of the cockpit to the other (in the same plane as the wing). So it will be only a foot or two from the headsets. Is this a bad idea?
>
> Sacha
> Kitfox IV

Receiving antennas do not radiate,
only transmit antennas: VHF Comm and Transponder



Bob . . .






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