VOR issues

Indiana_Pilot

Indiana_Pilot

Line Up and Wait
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Nov 2, 2013
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802
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Connersville, IN
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Flying "B"
My top VOR (VOR/ILS/LOC) tied to my KX155 is acting odd.. The ILS/LOC work fine (since it uses different frequencies than VOR)

When tuned to certain VORs it will read off 40 degrees or just jump around.. I could be 10 miles from it and it be off.. now I tune to another 40 miles away and it's rock solid. I have tried this with several VORs and it seems some frequencies work very well while others don't. My 2nd VOR works just fine. Example CVG 117.3 jumps no matter my location from it.. RID 110.6 is rock solid.

They are both using the same antenna (using a diplexer)

Has anyone else had experience with this? Can they be aligned? It seems like maybe they are off frequency? I hear audio just fine on them though..

I will take it to an avionics shop but like to troubleshoot myself too!
 
Very curious what you find out at the avionics shop.
 
While what you say is literally true, it is not actually a factor. The localizer uses the same frequency BAND as the VOR, but not the same frequencies. The LOC uses ODD decimal frequencies between 108 and 113 (108.1, 108.3, ... 112.9, etc), while the VOR uses EVEN decimal frequencies between these two limits (108.0, 108.2, ... 112.8 etc). Above 113, VOR uses the whole band. If it were anything except the internals to the radio, the LOC would be affected.

Jim
 
The more I think about it and read your posts.. I would think that if I hear the audio broadcast clear on the problem frequency then it is likely something in the VOR head itself.. Avionics shop can't get me in for another month! yikes!
 
weirdjim said:
While what you say is literally true, it is not actually a factor. The localizer uses the same frequency BAND as the VOR, but not the same frequencies. The LOC uses ODD decimal frequencies between 108 and 113 (108.1, 108.3, ... 112.9, etc), while the VOR uses EVEN decimal frequencies between these two limits (108.0, 108.2, ... 112.8 etc). Above 113, VOR uses the whole band. If it were anything except the internals to the radio, the LOC would be affected.

Jim
Click to expand...
What is different however, is the modulation. VORs use the phase difference of two transmitted signals to generate the angle. LOC just has two fixed signals that are compared in amplitude.
 
flyingron said:
What is different however, is the modulation. VORs use the phase difference of two transmitted signals to generate the angle. LOC just has two fixed signals that are compared in amplitude.
Click to expand...

As I vaguely recall, there were a couple of installations of phased LOC installations that SIMULATED VOR signals. Quite a kluge, and quickly went away.

Jim
 
If you're talking about the TLS there was exactly one installation (Watertown, WI) and never officially operational. However, it didn't use a simulated VOR, it used a simulated LOC and GS signals (i.e., it just broadcast the relative intensities from an omnidirectional antenna for what it wanted to display on the cockpit CDI/HSI).
 
I have nearly an identical issues with one of the planes I fly and it's baffling.

I can dial up an ILS/LOC just fine. I can ID the signal and the CDI reads correctly. When I dial up a VOR however, the CDI gives me a barber pole.
 
It's only baffling if your radio man can't fix it. As I pointed out the LOC and VORs are two different modulation schemes which the radio switches based on the frequency dialed in (as Jim pointed out initially). It's not surprising that your radio behaves differently. In addition, depending on the radio and the what you're using for a nav head, it's even less confusing. The thing that takes the OBS knob setting and the signal from the radio and translates that into needle deflection sometimes is inside the radio and sometimes it uses parts that are part of the head or otherwise exterior to the radio. The LOC doesn't give a hoot about OBS. All it does is drive the needle left or right depending on which tone is stronger.
 
If you have two CDIs that are the same part number one misbehaving and the other fine, I'd swap them and see if the problem follows. The same thing can be done with the radio itself.
 
bnt83 said:
If you have two CDIs that are the same part number one misbehaving and the other fine, I'd swap them and see if the problem follows. The same thing can be done with the radio itself.
Click to expand...

I wish I had the same heads.. the oddest part is that some VOR frequencies are perf fly fine.. really anything over 117MHz I have issues with 117.3 and 118.xx that I've noticed recently... the lower the frequency the more stable they are..


Sent from my iPhone using Tapatalk
 
flyingron said:
If you're talking about the TLS there was exactly one installation (Watertown, WI) and never officially operational. However, it didn't use a simulated VOR, it used a simulated LOC and GS signals (i.e., it just broadcast the relative intensities from an omnidirectional antenna for what it wanted to display on the cockpit CDI/HSI).
Click to expand...
Nope, I don't think it was TLS, and I'm not sure there ever WAS an operational one. It used some goofy phase modulation scheme that made the LOC detector THINK it was a difference in depth of modulation. But that was a LONG time ago and I'm sure that the details are on a dusty shelf somewhere.

Jim
 
Indiana_Pilot said:
I wish I had the same heads.. the oddest part is that some VOR frequencies are perf fly fine.. really anything over 117MHz I have issues with 117.3 and 118.xx that I've noticed recently... the lower the frequency the more stable they are..


Sent from my iPhone using Tapatalk
Click to expand...
That almost sounds like synthesizer on the jittery edge of lock.

Jim
 
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