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Occasional Com Radio Issue

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B2C2 View Drop Down
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    Posted: 16 May 2018 at 3:51pm
I have had an on and off problem with the radio quality on my 540 for a year or so and was wondering if anyone else has seen this. Once in a wile, I believe after a bit of a sit but haven't had it happen often enough to verify this, I will get comments from ground etc that my 540 com radio is 1 by 5. Reception is fine. I have two radios so I switch to the other one and all is good. Then it seems like after I power cycle the unit, typically next startup on the same day after a flight somewhere its fine. As you might imagine its not easy to diagnose this when the avionics shop is at another airport. So far it seems like it goes away by itself and I haven't been able to get it to do it at the shop. We checked all antenna connectors, tray etc and no obvious problems found. Has anyone else seen anything like this or have a suggestion of what might be causing it?    
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AzAv8r Quote  Post ReplyReply Direct Link To This Post Posted: 16 May 2018 at 10:53pm
I have had two incidents of something similar, both in mid February of this year.  The IFD was installed ~ Jul 15.

The first time I was contacting Ground for a day VFR departure, sitting near our hangar.  After several tries with no response, Ground replied "Aircraft repeatedly attempting to contact ground, nothing but a squeal." I switched to #2 (a Garmin SL30), Comms was fine, and we departed.  Later in the flight I did a radio check on the IFD with ATC and all was well, so we used the IFD for the remainder of the flight.  I attributed the issue to having the perfect (unlucky) position in an aluminum (hangar) canyon, out of line-of-sight from the tower, to maximize any of a number of RF distortions (I started life as a radio engineer).

Three days later departing a different airport, and sitting on a wide-open ramp in clear line-of-sight to the tower, Ground replied to my initial attempt "weak and unreadable".  I again switched to #2, and was successful.  We departed VFR on #2.  After a while in the flight, we switched back to the IFD and did a radio check with ATC.  No issues, so we used #1 for the remainder of the flight. 

Subsequent flights have revealed no issues.   Still scratching my head, and wishing I'd bought a lottery ticket.   Right now I'm assuming a defective antenna connection somewhere, but intermittent problems are difficult/expensive to track down until you discover the magic sequence that makes them repeatable.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote HenryM Quote  Post ReplyReply Direct Link To This Post Posted: 16 May 2018 at 11:16pm
i had a similar problem in a non-IFD-equipped plane. The root cause in my case was a loose ground connection. I accidentally found it when I touched a nut on the firewall that turned when it was supposed to be tight. We had spent a couple of hours chasing the bug right after an engine monitor installation in a Cessna 172. We were chasing leads related to the engine monitor installation which had not even touched the area where the loose ground was found. 

The loose ground caused the radio signal to react as described. Fortunately the ground was loose enough that it was not as intermittent as the problems described here. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PA20Pacer Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2018 at 7:07am
You have probably already thought about this, but often the #1 comm is wired to an antenna on the bottom of the plane. On the ground, it is possible for the plane to be positioned so that a wing or another part of the airframe is blocking the signal.

Regards,

Bob
Bob Siegfried, II
Brookeridge Airpark (LL22)
Downers Grove, IL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote compasst Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2018 at 11:39am
I experienced transmission clarity issues on my first IFD 540 shortly after it came out. Turns out it was a problem that required warranty work.

I knew it wasn’t antenna issues because the previous radio worked fine on same antenna and wiring.

Give tech a call and ask for Christine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote B2C2 Quote  Post ReplyReply Direct Link To This Post Posted: 18 May 2018 at 7:49pm
Ill try calling tech support. Given the extremely intermittent nature of the problem I'm not sure what they will say but its worth a shot. When you had this problem that was fixed under warranty was it also intermittent or predictably present?

In regards to one of the previous posts when I had the problem the other day i tried the radio again from a different spot on the field prior to departure to see if I was being blocked on the antenna due to the hangars nearby and had the same problem. Next time I'm going to power cycle the radio stack and see if it fixes it. I had a passenger with me and didn't want to unduly delay the flight with trouble shooting.   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Plunger Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 10:33am
I have a new IFD 440 with a different problem and can't get Avidyne Tech support to help me with. My situation is that the comm radio in the 440 has poor reception.I compare it to the comm 2 which is a 20 year old radio which receives perfectly. I swapped the antenna cables, for both radios but that didn't help. Next the avionics shop swapped out the 440 with a new unit off the shelf but the reception was still poor with the replacement radio. Next we reinstalled my old Garmin 430 and the reception was perfect.I have not replaced the coax cables or antennas yet.

Not sure what to do now. Rolland from Avidyne won't return my calls, the Avionics Place in Rockford is stumped. Not sure Avidyne was a good choice.

Anyone have any ideas?  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 1:34pm
I have never heard of anyone (customer, or shop) not getting return calls from Tech support, when they had an outstanding problem.

There is no general issue with the IFD COM section, if there was, it would have shown up a long time ago.

The thing that is common here would be the mounting tray. The fit on the IFD and GNS are a little different. I would bet that replacing the tray (if you didn't use the nice new IFD tray), might solve the problem.

Just a guess.

* Orest



Edited by oskrypuch - 24 May 2018 at 1:34pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Plunger Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 2:18pm
Orest, Thanks for the response I don't believe that Avidyne has an answer to this problem so it seems that their solution is to just ignore me.I went with the 440 so that I would not need to replace the tray and all of the expense associated with replacing my Garmin unit.

One theory that has been suggested is that possible the coax antenna cables could be the problem. Any thoughts?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gring Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 2:24pm
did you check to see if your squelch is on?  That will cause comm issues.  Aux page and audio tab.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Plunger Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 2:35pm
I have played with the squelch and don't believe that is the problem. Any signals will break the squelch much sooner on my old Bendix King (comm 2) before it will on the new 440. I turn off the squelch and I can hear a faint staticy signal while the comm2 is already receiving well.As I get closer to the signal source the reception improves but never gets a good as the old comm 2
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 4:21pm
Originally posted by Plunger Plunger wrote:

....
One theory that has been suggested is that possible the coax antenna cables could be the problem. Any thoughts?

Well, yes, something related to that or its connection to the new unit.

Has your shop tried to bench test the units? Any good avionics shop will have the tools to measure output. But rather unlikely that there were two faulty 440s in a row.

* Orest

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Plunger Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 5:31pm
The avionics shop did test with a power meter but not sure if that test will tell anything about reception. Tomorrow I will fly and see if I can get data on the transmitt quality. I have not had moments about the transmitt quality. So far I only know that reception is poor. I should know more tomorrow.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote B2C2 Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2018 at 3:50pm
I am not an install tech but suggest the following. Since two units both behave the same its almost certainly not the 440. It looks like the radio connects through a bulkhead pass through connector at the back of the tray. The antenna coax connects to the opposite end of this connector outside of the tray. I would suspect a problem with the IFD antenna coax connector to the tray bulkhead pass through connector connection. This could be caused by incomplete seating of the unit in the tray. It could also be that this bulkhead pass through connector is slightly out of spec or damaged due to the action of the Garmin unit on the connector. During one service visit with my 540 and an Avidyne tray the service tech had some trouble seating the 540 properly. its a tight fit. So I would double check the 440 is all the way seated. If that doesn't do it I would think about replacing the bulkhead pass through connector. These can be damaged and a poor connection will result in poor reception.   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote B2C2 Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2018 at 1:05pm
So I had the same issue when I went to fly the plane this last weekend, but this time I power cycled the radio stack in the run up area. Radio then worked properly. Problem solved. So I do think its associated with power up after sitting and it can for the moment be fixed by power cycling the unit,however this is the first time I have had it happen on back to back flights. Time for that call to tech support. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Plunger Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jun 2018 at 6:31pm
Is there anyone who knows what the part numbers are for the antennas that will work a IFD 440. This may be a long shot but an easy one to check for my poor reception problem. I Have not heard back from Avidyne in a while so will attempt to troubleshoot the comm problem.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DavidBunin Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jun 2018 at 4:14pm
I believe I used the CI-121 on mine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gring Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jun 2018 at 6:19am
The acceptable antennas are listed in the install manual available on the Avidyne website. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dmtidler Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jun 2018 at 7:43am
The install manuals used to be publicly available on the Avidyne website...not anymore.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AzAv8r Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jun 2018 at 9:28am
Unlike with GPS, any good quality comm antenna should work fine, as long as it is intact/undamaged.  By far the most likely issue with an antenna system is in the coax cable (including grounding) between the transceiver and the antenna.  Cables have an "impedance" determined by their physical cross-section dimensions and materials, so distortion (eg, kink it or tie it in a knot) can dramatically reduce their ability to deliver RF power.   Cuts in the shielding (which isn't just a shield, but part of the transmission line) can have this same effect.   The first time I was deep inside our panel (actually, when the IFD 540 was installed) I discovered the transponder antenna cable had been abraded through the shield on one side, which I'm sure meant we weren't radiating full transponder power. 

For a transmitter, the bad thing about an impedance problem is that part of the transmitter power gets reflected back into the transmitter itself, which distorts what signal does get transmitted.    So when the problem does happen, ask the person giving you the radio check (after you've switched to the good transmitter) about clarity.   That's why there is an "and" in the traditional radio check response "Loud and Clear", "Loud and distorted", "weak but readable", "weak and unreadable", etc..

Any chance you can correlate the issue to temperature?  I've seen bad BNC connectors where the center pin would barely mate with the female socket.  As materials shrink when they get cold perhaps you have a center pin pulling out of a connector.

Since the problem is intermittent, I would suggest swapping antenna and cable systems at the boxes themselves.   So your #1 comm will use your #2 antenna and cable, and vice-versa.   Fly this way until the problem is observed again.  If it follows the antenna, you'll know it's in the antenna system.  If it follows the radio, you'll know it is in the radio, the tray, or any coax pigtail between the tray and where you swapped the antenna systems.


Edited by AzAv8r - 06 Jun 2018 at 9:36am
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