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Occasional Com Radio Issue

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oskrypuch View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 29 Oct 2018 at 5:35pm
I concur, swapping out the tray would be the thing to try, only a few hours labor. There doesn't appear to be a design issue in the IFD COM radios, with thousands of units out there for a number of years now, if there was it would be obvious.

My IFD540 works quite well. The SL-30 I have as #2 is about the same in performance, and it is a very good unit.

If Avidyne even sent out three replacement units, looks like they did a yeoman effort. Even a modest non-connect of the antenna would explain your problems. The Avidyne trays are much better construction, for sure, try the tray swap -- very little to lose. 

* Orest



Edited by oskrypuch - 29 Oct 2018 at 5:38pm
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programmer@pcmforles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote programmer@pcmforles Quote  Post ReplyReply Direct Link To This Post Posted: 29 Oct 2018 at 8:46pm
Agreed.   I have also found before that if the BNC connector that is installed is not done properly the center contact does not stick out far enough and it will have an intermittent engagement with the backplate BNC connection.   I've accidentally done this before with the one crimper tool I had that I've since replaced.   On the IFD units the Com antenna connection is near the very top and often on a tight fit there is pressure on the com antenna coax with the glareshield or other things near the back of the firewall.   

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Post Options Post Options   Thanks (0) Thanks(0)   Quote PA23 Quote  Post ReplyReply Direct Link To This Post Posted: 02 Mar 2020 at 1:38pm
I know this is an old thread but I'm experiencing poor reception on the IFD440, replaced the COAX which was RG-58, now it is shiny new RG-400, no improvement, tried 2 different antennas, no improvement.

I'm going to work with my IA to test the VSWR (Avidyne wants this even though VSWR has very little bearing on reception).  We'll be using a "Sark-110 Antenna Analyzer" and provide the report to Avidyne.

This radio was a slide in replacement for a GNS430W, the 430W had no issues with receiving, even before replacing the antenna coax.

Jeff
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programmer@pcmforles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote programmer@pcmforles Quote  Post ReplyReply Direct Link To This Post Posted: 02 Mar 2020 at 11:23pm
Jeff, does your other com radio have any interference in it that varies with Engine RPM?   If so the IFD will pick up that interference and auto squelch it out and your reception will be poor.   This happened on my plane and a customer plane.    Turns out we both had spark plug/Mag ignition harnesses that were in bad condition that were radiating electromagnetic interference.   If I switched to one mag the noise went away, but was present on the other.   Put a new harness on mine and fixed the harness on the customer aircraft and both now have GREAT reception and range.   I did VSWR test both of them and they had SWR in the 1 to 1.5 range and the power output was 9 to 9.5 watts with .5 to 1 reflected back.    That indicates very good coax and antennas.
After these repairs my radios have been flawless and super clear.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote brou0040 Quote  Post ReplyReply Direct Link To This Post Posted: 03 Mar 2020 at 9:20am
Originally posted by programmer@pcmforles programmer@pcmforles wrote:

Jeff, does your other com radio have any interference in it that varies with Engine RPM?   If so the IFD will pick up that interference and auto squelch it out and your reception will be poor.   This happened on my plane and a customer plane.    Turns out we both had spark plug/Mag ignition harnesses that were in bad condition that were radiating electromagnetic interference.   If I switched to one mag the noise went away, but was present on the other.   Put a new harness on mine and fixed the harness on the customer aircraft and both now have GREAT reception and range.   I did VSWR test both of them and they had SWR in the 1 to 1.5 range and the power output was 9 to 9.5 watts with .5 to 1 reflected back.    That indicates very good coax and antennas.
After these repairs my radios have been flawless and super clear.


I believe I had a similar issue.  The issue was resolved when I changed the engine and redid the alternator, alternator wiring, ignition harnesses, overhauled mag, and more.  I can't isolate what fixed it since I did a bunch of work at once, but my theory was that the IFD was auto squelching such that I couldn't always hear with with the IFD radio when I could hear with the KX-155.
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PA23 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PA23 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Mar 2020 at 4:18pm
I have no noise whatsoever in the other radio, plus the antenna for the IFD is even further away from the engines than my #2 radio.

working with my IA I've sent over VSWR reading (VSWR of 2.20 from 118 - 136) to support which was taken from the front of the tray (pulled the radio and pushed a BNC female plug onto the connector in the tray) so I have the VSWR from the connection the radio uses through the coax to the radio. Support is looking for some logs now, hopefully I can get them tonight before my friend borrows the airplane for the weekend. 

If it matters, when I had the VSWR meter connection I performed also did TDR to get the cable length, the total length was just under 12 ft, (13 ft minus the 1 foot lead on the tester), cable is brand new RG400.


Edited by PA23 - 04 Mar 2020 at 4:21pm
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FlyingCOham View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FlyingCOham Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar 2020 at 1:33am
A VSWR of 2.2 isn't that bad (1.0 is perfect) but with a brand new RG400 cable and a properly tuned antenna I'd hope for something less than 2.0??
Jim Patton
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Post Options Post Options   Thanks (0) Thanks(0)   Quote B2C2 Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jul 2020 at 9:29pm
Well its been a while but I finally had this happen when I could try pulling the circuit breakers and I found that power cycling only the COM1 breaker for the radio section on the IFD fixed the issue. These breakers were installed new with the unit, so could be a bad/high resistance breaker, or the radio. At any rate there is a simple fix that doesn't require powering down the entire avionics stack. Now the queston is what to do about it.    
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