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nuckolls.bob(at)aeroelect
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 Posted: Sun Jul 10, 2011 8:54 am Post subject: PTT buzz |
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At 11:07 AM 7/10/2011, you wrote:
--> AeroElectric-List message posted by: Dan Billingsley <dan(at)azshowersolutions.com>
So I believe I may have narrowed it down to two possibilities if not both of
them adding to the issue...
1. I turned the intercom off and tried to transmit...I still got the buzz and it
is oscillating. My wife heard it broadcast on the HT and I heard her loud and
clear when she talked to me. I have not measured the voltage across the radio as
it is being keyed yet, however, my Dynon 100 indicates I my system voltage
(BATT) is at 11.3V. So Daniel, this may be part of it.
Any electronics that is qualified to install
in TC aircraft is operational down to 11.0 volts
or lower with full performance and stable with
reduced performance down to 9.0 volts.
2. As I was reading the Intercom install manual I found this entry interesting:
Electrical Noise IssuesWARNING: You must use separate shielded cables for
the microphone and headphone jacks. Combining
these two wires WILL cause loud oscillations and degrade
the intercom function. The oscillation is caused
by the cross-coupling between the large headphone
signal and the small microphone signal.
Hmmmm . . . I would like to see this demonstrated.
It is exceedingly difficult to 'cross couple' significant
energy between two parallel wires at these signal
levels. The headphone signal is larger . . . but not
that much larger.
So, realizing that the intercom is currently bypassed, should this warning still
be of concern? Remember I mentioned in a previous post that the headphone and
mic jacks were sent too short, so I cut them off behind the panel and spliced
them with Cat-5 cable. These jacks terminate behind the co-pilot.
OOPS! 26 AWG solid wire? It would have been better to
use extensions of 22AWG tie-wrapped into a bundle.
I would check these extensions very closely. What
you're describing now smells strongly of wiring error.
Bob . . .
[quote][b]
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enginerdy(at)gmail.com
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| Posted: Sun Jul 10, 2011 9:04 am Post subject: PTT buzz |
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You're using those jacks in your test even though the intercom is bypassed, right?
The unshielded wire feedback sounds more plausible than my other suggestions.
On Jul 10, 2011, at 11:07 AM, Dan Billingsley wrote:
| Quote: |
So I believe I may have narrowed it down to two possibilities if not both of
them adding to the issue...
1. I turned the intercom off and tried to transmit...I still got the buzz and it
is oscillating. My wife heard it broadcast on the HT and I heard her loud and
clear when she talked to me. I have not measured the voltage across the radio as
it is being keyed yet, however, my Dynon 100 indicates I my system voltage
(BATT) is at 11.3V. So Daniel, this may be part of it.
2. As I was reading the Intercom install manual I found this entry interesting:
Electrical Noise IssuesWARNING: You must use separate shielded cables for
the microphone and headphone jacks. Combining
these two wires WILL cause loud oscillations and degrade
the intercom function. The oscillation is caused
by the cross-coupling between the large headphone
signal and the small microphone signal.
So, realizing that the intercom is currently bypassed, should this warning still
be of concern? Remember I mentioned in a previous post that the headphone and
mic jacks were sent too short, so I cut them off behind the panel and spliced
them with Cat-5 cable. These jacks terminate behind the co-pilot.
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dan(at)azshowersolutions.
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| Posted: Sun Jul 10, 2011 11:19 am Post subject: PTT buzz |
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[quote]
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Sun, July 10, 2011 9:51:49 AM
Subject: Re: Re: PTT buzz
OOPS! 26 AWG solid wire? It would have been better to
use extensions of 22AWG tie-wrapped into a bundle.
I would check these extensions very closely. What
you're describing now smells strongly of wiring error.
Bob . . .
Very well, back to shielded wire all the way to the jacks.
Thanks for the input!
Dan
[b]
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jul 10, 2011 6:27 pm Post subject: PTT buzz |
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| Quote: |
Bob . . .
Very well, back to shielded wire all the way to the jacks.
Thanks for the input![/b] |
Not being shielded is no big deal whether the
mic and headset wires are bundled together or
not. Mic and headsets jacks should be insulated
from airframe and their respective grounds carried
to the intercom on separate wires. Twist them
as a pair (headset) and trio (mic) if it helps
keep them together. But I'm concerned about
gross connection error of some type that is
producing your feedback. Obviously, shielded
trios are very common and color coded to boot.
It's the easiest stuff to use so if you can find
some, go for it. I can send you some if you need
it.
Bob . . . [quote][b]
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dan(at)azshowersolutions.
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| Posted: Sun Jul 10, 2011 8:46 pm Post subject: PTT buzz |
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[quote]
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Sun, July 10, 2011 7:23:07 PM
Subject: Re: Re: PTT buzz
| Quote: |
Bob . . .
Very well, back to shielded wire all the way to the jacks.
Thanks for the input! |
Not being shielded is no big deal whether the
mic and headset wires are bundled together or
not. Mic and headsets jacks should be insulated
from airframe and their respective grounds carried
to the intercom on separate wires. Twist them
as a pair (headset) and trio (mic) if it helps
keep them together. But I'm concerned about
gross connection error of some type that is
producing your feedback. Obviously, shielded
trios are very common and color coded to boot.
It's the easiest stuff to use so if you can find
some, go for it. I can send you some if you need
it.
Bob . . .
Thanks Bob, Understood. The Approach guys told me when I discovered the lines were too short that they would send me some wire as well if I found I need it. I will go ahead and take them up on it.
Dan
[b]
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