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VOR reception and behavior
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362PC View Drop Down
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    Posted: 13 Jun 2024 at 3:43pm
I am currently working on my instrument rating and during a lesson yesterday we were having odd results with the VOR. 

Full Dynon Skyview HDX with IFD540. All other functions between the two seemingly working correctly through various flights and approaches.

With the VOR tuned to the correct frequency and only being 3 miles or so out the needle was jumping wildly from side to side. Crossing over the VOR typical behavior. Tracking outbound the identifier was dropping and returning and the needle was difficult to keep centered.  

The install is not quite a year old and I don't recall this being an issue during initial test flights. Antenna worked fine with previous avionics so it is doubtful that is the issue. with all other functions working properly what could be causing this?  No known NOTAMS on the station.
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rolfe_tessem View Drop Down
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Points: 190 		Post Options Post Options   Thanks (0) Thanks(0)   Quote rolfe_tessem Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jun 2024 at 8:52am
Not really an answer, but once you have your instrument rating you will probably never tune a VOR on your IFD again. I was one of Avidyne's earliest customers for the IFD540 and have never done it myself. In practice, if using a VOR as a waypoint, you'll use the GPS equivalent. I'm not aware of any VOR approaches left that don't have a better RNAV alternative, at least in my neck of the woods.

In the meantime, I would start troubleshooting with the antenna. How does it behave when tuning a localizer?

Rolfe
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rpostmo View Drop Down
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rolfe,  agree, but there seems to be more and more gps outages.
Bob
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Originally posted by rpostmo rpostmo wrote:

rolfe,  agree, but there seems to be more and more gps outages.
Have you actually experienced a problem getting a GPS fix, or are you just reading about such problems?

There have definitely been problems with GPS jamming in the Middle East and near the fighting in Ukraine.  However, I have not heard of any GPS availability issues in the US.  I live near a military base that issues NOTAMS several times a year for GPS outages in the region, and even so I have yet to see any affects to GPS availability in 15 years of flying.

That's not to say there's absolutely no reason to be concerned, but it is to say that I hear a lot more people pearl-clutching over GPS problems than I hear about actual GPS problems, at least in the US.
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I have had multiple GPS outages in flight, just flying around the southeastern US. Different hardware, different airplanes, different days. They are fairly rare, but they can happen… and not just when there are announced outages due to jamming testing.

(And, fun fact, the jamming exercises the military does move around; there was one last week centered near Mobile, Alabama that spread across most of Alabama and Mississippi and a good chunk of Georgia-- not the usual areas near White Sands, offshore Norfolk, etc.)


Edited by paulr - 18 Jun 2024 at 9:17am
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rpostmo View Drop Down
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I've not had one, but in planning my trip to Sun-N-Fun this year, the briefing included warnings for
GPS outages such that I rerouted slightly to be on a VOR friendly track.  
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birddog486 View Drop Down
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Originally posted by 362PC 362PC wrote:

I am currently working on my instrument rating and during a lesson yesterday we were having odd results with the VOR. 

Full Dynon Skyview HDX with IFD540. All other functions between the two seemingly working correctly through various flights and approaches.

With the VOR tuned to the correct frequency and only being 3 miles or so out the needle was jumping wildly from side to side. Crossing over the VOR typical behavior. Tracking outbound the identifier was dropping and returning and the needle was difficult to keep centered.  

The install is not quite a year old and I don't recall this being an issue during initial test flights. Antenna worked fine with previous avionics so it is doubtful that is the issue. with all other functions working properly what could be causing this?  No known NOTAMS on the station.

What antennae are you using? I've had the same issue with my IFD440 and HDX since install and Testing the VOR with a signal generator at the last condition inspection had a perfectly stable needle.(strange)

Not sure what the issue is but sitting on the ground looking at the Vortac I have the same wagging needle as I do 100 miles from the VOR. I've also tested the SWR and it's below 1.5

Here's a short video on the ground looking at the VOR https://youtu.be/KXOHCPbbiJA



Edited by birddog486 - 19 Jun 2024 at 5:34pm
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362PC View Drop Down
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Points: 13 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 362PC Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 2024 at 1:38pm
not sure on the antenna make or model, they were in the plane when purchased 2 years ago, connected to steam gauges / CDIs / Garmin 430 and worked correctly with those instruments. 
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362PC View Drop Down
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Points: 13 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 362PC Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jul 2024 at 7:43pm
update... we found the antenna cables were frayed near the connections to the antennas atop the tail. redid the heat shrink and there is no longer any issues with the needles.  happy it was an easy fix.
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