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Wagging VOR needle

birddog486

Well Known Member
I've been trying to track down the interference thats causing my Dynon HDX VOR needle to slowly/randomly wag up to 3 degrees back and forth without any luck.

I'm using the Archer NAV wingtip antenna tied to RG400 connected to a RAMI diplexer to an IFD440. It gets crystal clear morse code 60+ miles away and flying a localizer at almost 20 miles the needle is rock steady but the VOR wagging happens weather near or far from the station.

It doesn't make any difference with lights or strobes on or off. I've also removed power from the dynon roll servo and still no change.

I'm tempted to turn off the mags one at a time next because I'm out of ideas.

I ran across an article written by Bob Archer saying there were issue with newer glass panels and the wingtip antenna's but It didn't talk about a fix to the problem.

Anyone have this happen and come up with a fix?
 
Dont think scallopings the issue, it has the same behavior at all altitudes and acts the same if I'm at 1 mile or 60 on all the VOR's I've tested.
 
Scalloping can be caused by a weak RF signal coming from the antenna. I had one Archer antenna, with a splitter feeding two nav radios. The scalloping happened on the ILS needle; the archer antenna has a good VSWR for VOR but the VSWR degrades at the higher (2x) ILS frequencies. The splitter halved the power which only compounded the problem. Poor VSWR is less RF energy making it to the radio. I cured my problem with a separate archer antenna for each nav radio. Do you know someone with a VSWR meter? I'd check there first- check the VSWR at the coax that plugs into the radio, then work backwards if needed. A ham radio buddy would be a good place to start; also radio shops have VSWR meters.
 
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Nope, ILS frequency is about the same as VOR. Glide Slope frequency is three times the VOR frequency. All such quarter and half wavelength antennas work just fine at three times it’s base frequency.

Splinters do cut the signal by 3db, but they also cut the background noise by 3db. Your receiver is interesting in signal to noise ratio, not just signal strength. While there is a point of no return, for most applications adding a splitter has little practical impact.

Carl
 
I've got a clean antenna setup, following very closely all Bob's installation instructions. Here is my measured data using a RigExpert antenna analyzer:

112 Mhz +-6 Mhz: VSWR < 1.9
333 Mhz +- 3 Mhz: VSWR < 6.0

Archer's antenna is tuned to the VOR frequency, however it falls off at the glide slope frequencies, which isn't a surprise.
 
I've been trying to track down the interference thats causing my Dynon HDX VOR needle to slowly/randomly wag up to 3 degrees back and forth without any luck.

I'm using the Archer NAV wingtip antenna tied to RG400 connected to a RAMI diplexer to an IFD440. It gets crystal clear morse code 60+ miles away and flying a localizer at almost 20 miles the needle is rock steady but the VOR wagging happens weather near or far from the station.

It doesn't make any difference with lights or strobes on or off. I've also removed power from the dynon roll servo and still no change.

I'm tempted to turn off the mags one at a time next because I'm out of ideas.

I ran across an article written by Bob Archer saying there were issue with newer glass panels and the wingtip antenna's but It didn't talk about a fix to the problem.

Anyone have this happen and come up with a fix?

You may want to check to be sure that your Archer antenna is well grounded to the wing skin metal. In my case, I was relying on the wing tip fasteners and nut-plates that were riveted through the antenna to provide a ground to the wing skin. This was insufficient, so I used adhesive-backed copper foil wrapped around the edge of the wingtip flange (and under the antenna) to provide a more robust ground path to the wing-skin for a good ground plane.

Skylor
 
You may want to check to be sure that your Archer antenna is well grounded to the wing skin metal. In my case, I was relying on the wing tip fasteners and nut-plates that were riveted through the antenna to provide a ground to the wing skin. This was insufficient, so I used adhesive-backed copper foil wrapped around the edge of the wingtip flange (and under the antenna) to provide a more robust ground path to the wing-skin for a good ground plane.

Skylor

The antennas mounted under 4 or 5 nutplates and the wingtip is screwed on so, I assume it's grounded well enough because the planes polished but, I'll look into that.

Sounds like finding an analyzer/VSWR meter is next, I think because the morse code is loud and clear the radial would be stable but maybe thats not the case
 
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"What's a VOR" You know, in the last couple of years the "signal" from
a "VOR" seems to have been getting weaker. Really, seems like it.
And yes, my radios are getting older, if it has a VOR. Maybe the government is turning down the power on the VOR transmitter to save on electricity.

In my state (Ohio) there will be only two VOR's left when the end comes. That's what they said a few years ago.

My Loran doesn't seem to work either.

John
 
RPM

Might try changing RPM. Mag noise and propeller modulation of the signal can cause VOR waggle. Easy to check. Modern circuitry may have reduced it some. Used to be a common complaint.

Ron
 
I took a short video of whats happening. There's some turbulence and a few degrees of heading change but I'm about 25 miles from the VOR.

It should take 10 seconds or more flying 90 degrees to the radial to get this much needle deflection. I've tried another antenna and got the same result so unfortunately I may need to take it to a shop.

https://youtu.be/WjxxxERLEfo
 
Box

Wow. Looked at the video. The CDI is all over the place. There is no periodicity, just random wandering. So beat frequency and even scalloping is very unlikely. Did a lot of flying and a lot of bench work way back. Don't remember seeing anything quite as unstable as that.

Fairly certain it's a bad box, looks like some component dying in the vor processing circuity. The loc signal processing path is different. Since the loc function is reported rock solid, the install is probably fine.

Ron
 
Wow.
Fairly certain it's a bad box, looks like some component dying in the vor processing circuity. The loc signal processing path is different. Since the loc function is reported rock solid, the install is probably fine.

Ron

Can you park at an airport where a vor can be received on the ground? If the needle still wags like this, it’s likely the electronics.
 
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