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kenharrison
Joined: 06 Aug 2008
Posts: 4
Location: Lancaster, SC
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 Posted: Mon Dec 15, 2008 5:00 am Post subject: Transponder Noise with Rotax 582 |
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Hello Gentlemen,
I’m having transponder trouble. I have installed a “new” KT76 in my Kitfox III with 582 Mod 90. I am running BR8ES plugs and have a Key West regulator/rectifier. So far I have been very happy with the system and have very low/acceptable RF noise in the radio/intercom. The radio is a handheld on the 12V from the aircraft, and the intercom is a David Clark in panel (can’t remember the model at the moment). I have installed and wired the transponder according to the directions (relatively certain about that). With the engine not running, if I turn the transponder on it powers up and cycles through its test normally. It appears to ident and test properly as any other transponder I’ve used in other aircraft, and it appears to be receiving interrogation from ATC, and returning responses normally (the light blinks periodically). My problem is that when the 582 is running, the transponder will immediately start blinking incessantly and I get a crackling sound over the intercom.
Does anyone have any ideas what I’ve done wrong. I have not had the transponder certified by the shop yet. Was hoping to clear up this problem before I take it to them. I have searched high and low on the internet and on the Kitfox archives and on Aeroelectric.com but can find any discussion of such a problem.
I would appreciate any guidance.
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_________________
Ken Harrison
Kitfox III
Rotax 582 C Box
Powerfin 3-Blade |
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Fox5flyer
Guest
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| Posted: Mon Dec 15, 2008 5:08 am Post subject: Transponder Noise with Rotax 582 |
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There probably isn't anything wrong with the transponder. Sounds like
you're getting ignition interference. Check all of your wiring and ensure
none of the transponder wiring (especially antenna) is close to ignition
wiring.
Deke Morisse
Mikado Michigan
S5/Subaru/CAP 402+ TT
"The aim of an argument or discussion should not be victory, but progress."
- Joseph Joubert
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Paul A. Franz, P.E.
Joined: 02 Dec 2008
Posts: 280
Location: Bellevue WA
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| Posted: Mon Dec 15, 2008 6:05 am Post subject: Transponder Noise with Rotax 582 |
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On Mon, December 15, 2008 5:00 am, kenharrison wrote:
| Quote: |
My problem is that
when the 582 is running, the transponder will immediately start blinking
incessantly and I get a crackling sound o!
ver the intercom.
Does anyone have any ideas what I’ve done wrong. I have not had the transponder
certified by the shop yet. Was hoping to clear up this problem before I take it to
them. I have searched high and low on the internet and on the Kitfox archives and on
Aeroelectric.com but can find any discussion of such a problem.
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You're going to need to do some isolation tests. The noise described could be coming
from either the charging circuit (alternator/lighting coil and VR) or it is coming
from the ignition. If any of the wiring is coaxial cable make sure it is only grounded
on one end of the coax shield. Which end? That's somewhat important too but I can't
answer that with certainty. You're likely going to need a couple of low pass noise
filters too.
You would do well to post this on the aeroelectric list. I've seen many discussions in
the past about line noise. You can post without being subscribed to any maillist. You
only need to be subscribed to matronics. When you post there you can flag your message
to get a notification by e-mail when someone responds.
<http://forums.matronics.com/>
This system works so well, that I see no need to subscribe to any lists because once
you're signed up on matronics, all lists are accessible.
--
Paul A. Franz
Registration/Aircraft - N14UW/Merlin GT
Engine/Prop - Rotax 914/NSI CAP
Bellevue WA
425.241.1618 Cell
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_________________
Paul A. Franz, P.E.
Registration/Aircraft - N14UW/Merlin GT
Engine/Prop - Rotax 914/NSI CAP
Bellevue WA
425.241.1618 Cell
425.440.9505 Office |
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n85ae
Joined: 14 Mar 2007
Posts: 403
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| Posted: Mon Dec 15, 2008 9:34 am Post subject: Re: Transponder Noise with Rotax 582 |
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Check make sure that you have a decent size grounds from your avionics to battery (-), if you're using airframe as ground you might want to look
into running independent grounds to your devices. Also connect a ground
to the encoder case, especially if you have it adel clamped to the frame.
Regards,
Jeff
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mikeperkins
Joined: 22 May 2007
Posts: 123
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| Posted: Tue Dec 16, 2008 2:12 pm Post subject: Re: Transponder Noise with Rotax 582 |
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Jeff is right in suggesting that you check the ground connection; ground connections are often the source of radio noise.
A troublshooting procedure is this:
You need to know if the transponder is being disturbed by the RF input (antenna input) or by the power source. A quick way to check this is to remove the antenna connector right at the transponder and see if the the funny operation goes away. If it still acts funny, power the transponder from a separate 12 v battery (not suggesting this as a solution, just a test).
The old transponders like the KX76 don't have much power filtering. I'd be surprised if the transponder's problem here was something other than noisy power. It's hard to fool a transponder to think it's receiving radar signals, but it's easy to make them misbehave with noisy power. The above tests will tell you.
Mike Perkins
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mikeperkins
Joined: 22 May 2007
Posts: 123
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| Posted: Tue Dec 16, 2008 2:22 pm Post subject: Re: Transponder Noise with Rotax 582 |
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Post script to my troubleshooting procedure - - If you see transponder replies with the antenna disconnected, shut the transponder down pretty quickly - KX76s don't like transmitting for very long without an antenna connected, but a few seconds won't hurt.
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Tue Dec 16, 2008 7:53 pm Post subject: Transponder Noise with Rotax 582 |
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Try powering your Xpndr with an independent battery. If it cycles properly then you know you have a lot of noise coming in on the B+ line. If the Xpndr continues to have start up issues while on an independent battery then you have too much RFI from your engine.
The thing to do is first of all to be sure that the resistor caps are still intact. The 582 is the exception that makes the rule about using both resistor plugs and caps... You should be using both.
The next thing is to check all your grounds. Make sure they are all clean and tight to the frame of the plane. I expect that more than 90% of the problems people have with avionics can be traced to poor grounds. While you are at it check there is a good heavy jumper that goes across the rubber "Lord" mounts of the engine... Those mounts make great insulators and control cables make poor grounds.
Finally check the coaxial cable on the transponder. Make sure it hasn't been pinched or cracked try to position the antenna on the bottom of the plane as far away from the engine as practical.
Be suer to let us know how things work out.
Noel Loveys
AME Intern, RPP
Kitfox III-A,
Aerocet 1100 floats
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_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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