Today's Message Index:
----------------------
1. 07:44 AM - Re: Radio Buzz.......................NO More (Ross Home)
2. 08:41 AM - Re: Radio Buzz.......................NO More (Robert L. Nuckolls, III)
3. 09:03 AM - VOR antenna question (Robert L. Nuckolls, III)
4. 09:48 AM - Re: VOR antenna question (William Hibbing)
5. 02:56 PM - Re: VOR antenna question (Robert L. Nuckolls, III)
Message 1
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| Subject: | Radio Buzz.......................NO More |
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@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Ross Home
Sent: Monday, July 20, 2015 9:14 AM
Subject: RE: AeroElectric-List: 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@matronics.com
<mailto:owner-aeroelectric-list-server@matronics.com>
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: Monday, July 20, 2015 6:12 AM
Subject: Re: AeroElectric-List: Radio Buzz
At 06:16 PM 7/19/2015, you wrote:
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 . . .
http://www.matronics.com/Navigator?AeroElectric-List
http://forums.matronics.com
http://www.matronics.com/contribution
Message 2
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| Subject: | Radio Buzz.......................NO More |
At 09:42 AM 7/23/2015, you wrote:
>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 . . .
Message 3
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| Subject: | VOR antenna question |
At 06:47 AM 7/22/2015, you wrote:
Hi, Bob -
I have a 1962 Skylane, and I am not satisfied
with its VOR/GS performance at all. Add to that
the fact that the autopilot won't track worth a
damn, and I'm wondering if the Nav receiver/antenna setup is at fault.
How steady is the CDI display when receiving VOR? Are
the CDI warning flags lifted? Could you hand-fly the
airplane accurately using the display? If so, then
it seems unlikely that quality of data from VOR Rx
to AP is probably not the issue. If the
CDI warning flags are not dropping, then your
tracking problem is probably centered elsewhere.
I've decided to do a little troubleshooting
before I send the S-Tec 55x in for a major
(expensive) overhaul.=C2 At the very least, I want
to replace the VOR/GS coax and balun (The antenna
is a horizontal dipole on the top of the vertical stabilizer, like many
182s).
The balun is a typical made-from-coax affair that
has never been changed since the airplane was new
in 1962, as far as I can tell.=C2 I'm sure it has
drowned in water - or at least moisture - for a
very long time.=C2 The dipole is then just connected directly to the balun.
My questions are these:
1. The first thing is to replace the long run of
coax. What coax do you recommend? I know RG 58
will work (50 ohm), but I've heard there are much
better, lower-loss cables for this application.
Yes. A much more robust and lower loss product
like RG141/142/400 is never a bad bet. There
are less expensive 50-ohm coaxes with better
performance than RG58 like the LMR195, same
size and connectors as RG58, similar outside
insulation but better shield construction and
lower loss insulation around the center
conductor . . . but a little fussier to work
with than the double-shield, Tef-like products
cited earlier. I'd go with 141/142/400 but the
195 is fine too.
2. From what I read, the only purpose of the
balun is to keep RF off the braid on the coax;
the balun's matching function really doesn't do much for performance.
Yes. "Keeping RF of the braid" is a transmitting
issue . . and yes, it takes laboratory grade
instrumentation and observation methods to
deduce any benefits for adding the balun to
a VOR antenna. All other things being equal,
the pilot would not be able to tell whether
or not a balun was installed.
Since this is a receive-only setup, do I even
need to worry about a balun, or could I just
connect my new coax (unbalanced) to the antenna and forget about it?
We built thousands of airplanes at Cessna in the 60's
and 70's that were wired that way . . . and VOR performance
of vacuum tube receivers was deemed adequate. And
again, all things being equal, the pilots would not
know if a balun was present or not.
3. If you think a balun is worth it, where can I
find a decent 1:1 potted balun, so I don't have
to worry about fabricating a new coax one?
If the airplane's factory-delivered configuration
included a balun, then there's always risk of running
afoul of the TC-rule-gods.
They're easy to build, especially from RF141/142/400
coaxes that will readily stand off the effects of
soldering.
http://tinyurl.com/yytxwd3
So it's kinda your choice. A fresh hunk of modern
coax simply tied to the VOR whiskers will perform
nicely. Whether or not this produces better VOR/AP
performance is problematic.
Bob . . .
Message 4
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| Subject: | Re: VOR antenna question |
Give Kenny Poyner=C2- a call at 817-215-7637 (Cobham) and explain the sit
uation to him.=C2- He is a whiz at the S-Tec a/p's and can be very helpfu
l.=C2- Bill
On Thursday, July 23, 2015 11:05 AM, "Robert L. Nuckolls, III" <nuckol
ls.bob@aeroelectric.com> wrote:
At 06:47 AM 7/22/2015, you wrote:
Hi, Bob -
I have a 1962 Skylane, and I am not satisfied with its VOR/GS performanceat
all. Add to that the fact that the autopilot won't track worth a damn,and
I'm wondering if the Nav receiver/antenna setup is at fault.
=C2-=C2- How steady is the CDI display when receiving VOR? Are
=C2-=C2- the CDI warning flags lifted? Could you hand-fly the
=C2-=C2- airplane accurately using the display? If so, then
=C2-=C2- it seems unlikely that quality of data from VOR Rx
=C2-=C2- to AP is probably not the issue. If the
=C2-=C2- CDI warning flags are not dropping, then your
=C2-=C2- tracking problem is probably centered elsewhere.
I've decided to do a little troubleshooting before I send the S-Tec 55xin f
or a major (expensive) overhaul.=C3=82=C2- At the very least, I want tore
place the VOR/GS coax and balun (The antenna is a horizontal dipole onthe t
op of the vertical stabilizer, like many 182s).
The balun is a typical made-from-coax affair that has never been changedsin
ce the airplane was new in 1962, as far as I can tell.=C3=82=C2- I'm sure
it has drowned in water - or at least moisture - for a very longtime.=C3=82
=C2- The dipole is then just connected directly to thebalun.
My questions are these:
1. The first thing is to replace the long run of coax. What coax do youreco
mmend?=C2- I know RG 58 will work (50 ohm), but I've heard thereare much
better, lower-loss cables for this application.
=C2-=C2-=C2- Yes. A much more robust and lower loss product
=C2-=C2-=C2- like RG141/142/400 is never a bad bet. There
=C2-=C2-=C2- are less expensive 50-ohm coaxes with better
=C2-=C2-=C2- performance than RG58 like the LMR195, same
=C2-=C2-=C2- size and connectors as RG58, similar outside
=C2-=C2-=C2- insulation but better shield construction and
=C2-=C2-=C2- lower loss insulation around the center
=C2-=C2-=C2- conductor . . . but a little fussier to work
=C2-=C2-=C2- with than the double-shield, Tef-like products
=C2-=C2-=C2- cited earlier. I'd go with 141/142/400 but the
=C2-=C2-=C2- 195 is fine too.
2. From what I read, the only purpose of the balun is to keep RF off thebra
id on the coax; the balun's matching function really doesn't do muchfor per
formance.
=C2-=C2-=C2- Yes. "Keeping RF of the braid" is atransmitting
=C2-=C2-=C2- issue . .=C2- and yes, it takes laboratorygrade
=C2-=C2-=C2- instrumentation and observation methods to
=C2-=C2-=C2- deduce any benefits for adding the balun to
=C2-=C2-=C2- a VOR antenna.=C2- All other things beingequal,
=C2-=C2-=C2- the pilot would not be able to tell whether
=C2-=C2-=C2- or not a balun was installed.
Since this is a receive-only setup, do I even need to worry about abalun, o
r could I just connect my new coax (unbalanced) to the antennaand forget ab
out it?
=C2-=C2-=C2- We built thousands of airplanes at Cessna in the60's
=C2-=C2-=C2- and 70's that were wired that way . . . and VORperforman
ce
=C2-=C2-=C2- of vacuum tube receivers was deemed adequate. And
=C2-=C2-=C2- again, all things being equal, the pilots wouldnot
=C2-=C2-=C2- know if a balun was present or not.
3. If you think a balun is worth it, where can I find a decent 1:1 pottedba
lun, so I don't have to worry about fabricating a new coaxone?
=C2-=C2- If the airplane's factory-delivered configuration
=C2-=C2- included a balun, then there's always risk of running
=C2-=C2- afoul of the TC-rule-gods.
=C2-=C2- They're easy to build, especially from RF141/142/400
=C2-=C2- coaxes that will readily stand off the effects of
=C2-=C2- soldering.
http://tinyurl.com/yytxwd3
=C2-=C2- So it's kinda your choice. A fresh hunk of modern
=C2-=C2- coax simply tied to the VOR whiskers will perform
=C2-=C2- nicely. Whether or not this produces better VOR/AP
=C2-=C2- performance is problematic.
=C2- Bob . . .
Message 5
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| Subject: | Re: VOR antenna question |
At 11:46 AM 7/23/2015, you wrote:
>Give Kenny Poyner a call at 817-215-7637 (Cobham) and explain the
>situation to him. He is a whiz at the S-Tec a/p's and can be very helpful.
>Bill
Thanks for the heads-up Bill, I've forwarded the suggestion
to Jim . . .
>On Thursday, July 23, 2015 11:05 AM, "Robert L. Nuckolls, III"
><nuckolls.bob@aeroelectric.com> wrote:
>
>
>At 06:47 AM 7/22/2015, you wrote:
>Hi, Bob -
>
>
>I have a 1962 Skylane, and I am not satisfied with its VOR/GS
>performance at all. Add to that the fact that the autopilot won't
>track worth a damn, and I'm wondering if the Nav receiver/antenna
>setup is at fault.
Bob . . .
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