VOR/ILS needle oscillation

NealRomeoGolf

NealRomeoGolf

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Trying to get some of the last gremlins out of my plane and up come new ones. I have now installed a Garmin GNC255A for my Com/Nav2 radio. It goes through my Garmin G5 HSI. Since I am getting ready for my IR training, I decided on the flight today to track a VOR and then make sure I had needles for an ILS. As I tracked the VOR, the HSI needle would oscillate back and forth (left and right of center). The ILS did the same but seemed to be less pronounced. The glideslope did not oscillate. Is this an antenna problem? Electrical interference?
 
Sounds like "scalloping" and is a natural phenomenon.
I had never heard of it either until I read my owner manual for my KX-145 (horrendous com/nav) from the 70's.
 
No, it is not normal assuming you don’t fly like you are drunk.
 
It sounds to me like it could be an antenna or balun problem. You can also slide the radio out and clean the contacts with an electronic contact cleaner spray. I have done that and had it help a lot. I had to use a plastic soda straw to get the spray to the back of the tray where it needed to be. An avionics shop would be able to check things out for you. Don't give up. :)
 
I'd try a couple different vors and localizers. Some of them can be pretty funky.
 
NealRomeoGolf said:
Trying to get some of the last gremlins out of my plane and up come new ones. I have now installed a Garmin GNC255A for my Com/Nav2 radio. It goes through my Garmin G5 HSI. Since I am getting ready for my IR training, I decided on the flight today to track a VOR and then make sure I had needles for an ILS. As I tracked the VOR, the HSI needle would oscillate back and forth (left and right of center). The ILS did the same but seemed to be less pronounced. The glideslope did not oscillate. Is this an antenna problem? Electrical interference?
Click to expand...

Is it doing this only with the NAV 2 up on the HSI, but not the NAV 1 using the same VOR & ILS?
 
NealRomeoGolf said:
Trying to get some of the last gremlins out of my plane and up come new ones. I have now installed a Garmin GNC255A for my Com/Nav2 radio. It goes through my Garmin G5 HSI. Since I am getting ready for my IR training, I decided on the flight today to track a VOR and then make sure I had needles for an ILS. As I tracked the VOR, the HSI needle would oscillate back and forth (left and right of center). The ILS did the same but seemed to be less pronounced. The glideslope did not oscillate. Is this an antenna problem? Electrical interference?
Click to expand...

How fast did it oscillate?
 
Incidentally, I had a similar issue.
The avionics shop lent me a replacement CDI to test. If the oscillation remained -> radio/antenna issue. If the oscillation ceased -> bad CDI.
It was a bad CDI.
 
NealRomeoGolf said:
I didn't check Nav1 (530W) so will need to do that next time.
Click to expand...

You need to isolate whether it's the NAV source or the G5.
I presume your NAV 1 and NAV 2 share the same VOR antenna?
Do you have a separate CDI, or only the G5 HSI?

Also, great to hear about the IR. You'll enjoy the challenge and sense of accomplishment I hope! It was the rating I had the most fun training for.
 
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GRG55 said:
You need to isolate whether it's the NAV source or the G5.
I presume your NAV 1 and NAV 2 share the same VOR antenna?
Do you have a separate CDI, or only the G5 HSI?

Also, great to hear about the IR. You'll enjoy the challenge and sense of accomplishment I hope! It was the rating I had the most fun training for.
Click to expand...
I only have the G5.

Been chomping at the bit for the IR. Instructors are not aplenty here. Plus the whole 2 months down for the prop overhaul didn't help.
 
I used to fly a C421 that the loc would do that unless you bumped the the props up to the top of the green. Something about the harmonic interference at certain prop rpms.
 
Seems to be electrical interference from the strobes. Went up for my first IR lesson today (finally!) and were doing holds. Needle was oscillating again (different VOR from last week) so we switched the strobes off and the oscillation went away. Put the strobes back on and it stayed fine. Go figure.
 
^ the vagaries of our old planes. Hope the fix is a simple one. Folks chase the loc early in IR training. The visual of chasing an oscillating loc is nutty.

Sent from my SM-G960U1 using Tapatalk
 
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