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rossmickey(at)comcast.net
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 Posted: Thu Jul 23, 2015 6:44 am Post subject: Radio Buzz.......................NO More |
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Yesterday, I unpinned the 18” piece of unused OAT cable as well as three unused “input” wires that were connected to my AFS 5600 main harness as well as grounding the serial port shield to the chassis. I am happy to say that both radios are clear as a bell.
Thank you all for your help in identifying the problem. One step closer to getting my baby back into the air.
Ross Mickey
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Ross Home
Sent: Monday, July 20, 2015 9:14 AM
To: aeroelectric-list(at)matronics.com
Subject: RE: Radio Buzz
With my dumbed down handheld sniffer I have identified the major culprit and perhaps a second. The main interference (80%-90%) is from an 18” piece of unused OAT wire that is plugged into the main harness with pos, signal and shield all pinned in the harness. In talking with AFS tech support, the three options are, 1) connect the pos and signal wires together 2) connect the signal and shield together or 3) unpin all three wires from the harness and remove the whole thing.
The second culprit is a couple of the serial port wires (2 of the 4). These are emanating some interference which is probably caused by my error. I connected a black the wire coming out of the premade harness (which is connected to the four shield wires for the serial ports) to ground rather than to the chassis of the EFIS. The new harnesses from AFS (mine is two years old) do not have this but take care of connecting the serial shields to the chassis in the pinning of the harness.
I will check these out on Weds when I get back to the hangar.
Thank you all for your help.
Ross
From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) [mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Robert L. Nuckolls, III
Sent: Monday, July 20, 2015 6:12 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: Radio Buzz
At 06:16 PM 7/19/2015, you wrote: | Quote: |
I will try to rig a short antenna. As it is, I get about 6-9 inches from the EFIS to set off the sniffer (a handheld radio)
Ross Mickey |
Your zeroing in on the root cause . . . I have
an h-t antenna that's only about an inch long with
a 1/2" disk soldered to the end. This can be used
to probe wires, openings in enclosures, lcd screens,
etc.
Of course, this only works with noise sources that have
strong amplitude modulated components . . . but if you
can 'hear' it in your nav-comm, you can generally 'sniff
it' with a hand-held.
Bob . . . 012345678901234567
[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jul 23, 2015 7:41 am Post subject: Radio Buzz.......................NO More |
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At 09:42 AM 7/23/2015, you wrote:
| Quote: | Yesterday, I unpinned the 18” piece of unused OAT cable as well as three unused “input” wires that were connected to my AFS 5600 main harness as well as grounding the serial port shield to the chassis. I am happy to say that both radios are clear as a bell.
Thank you all for your help in identifying the problem. One step closer to getting my baby back into the air.
Ross Mickey |
Thank you for bringing this to the List . . . this
has been a useful demonstration of the value for
tracking down root cause, propagation mode and
mitigation of an unfriendly transfer of energy
from one system to another.
It's all physics . . . when boiled down to the
controlling simple-ideas, the fix becomes simple
as well. Our science and art of building and
operating successful aircraft is burdened
with a lot of guessing, too little understanding
and most important, a lack of interest.
For most of my tenure at Beech, I was chartered
and financed independently of project budgets
to track down and identify such things.
I wrote perhaps a dozen white papers
describing the efforts, discoveries, deductions
and remedies for a variety of antagonists . . .
some of costing hundreds of thousands of dollars
in warranty, re-certification and/or lost
customer confidence.
But as of this writing, I'll bet any one of
those situations could pop up again at the new
Textron . . . and nobody would remember that
we had been there, done that. They'll struggle
through it all over again.
This is why it is so important that the any
'new' problem be approached with the same
kind of inquiry and deduction that folks are
expected to exercise when figuring out that
Col-Mustard-did-it-in-the-library-with-a-gun.
The processes are identical.
Bob . . . [quote][b]
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