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Nav audio high static weak morse code

dbaflyer

Well Known Member
I have a GMA240 audio panel. The GTN650 has the P1004 connector pins 16/17 (VOR/ILS Audio Hi/Low) wired to the audio panels pin 16/17 (NAV 1 Hi/Low).

In my hangar with only the avionics powered the morse code audio is useable but does have a bit of background static.

In the air or on the ground with engine running, the morse code is not even useable. The static seems louder and the signal seems weak. The VOR receiver works fine when tracking radials, etc.

When the engine running on the ground I've turned off alternator and strobe. This matches the reasonable signal I got in the hangar, but with the engine running. Although now that I'm sitting here, I should have also tried turning on/off the ignition. I have one Magneto and an EFII ignition coil

Any other trouble shooting ideas would be appreciated.
 
Are you sure the morse code filter is off? e.g., with the 650 in nav mode (so the volume control adjusts the nav volume) do you see ‘ID’ up in the frequency box? If no, push and release the volume knob. Now you should see ‘ID’ and hear the morse code.
 
The archer wing tip antennae installed in right wing tip. This is not a new issue, but can't say I've tried to identify a VOR until now since I'm doing IFR training.

The com radio is also fine with no noise

The morse code filter is/was off. The ID was shown in the nav box. In the hangar it's useable, but I was at the VOR checkpoint today with engine on and you can barely hear some morse code but with a lot of static. Also in an actual flight Thursday it was basically not useable.
 
If you are receiving VOR stations at ~100nmi at altitude, then the nav ID issue is associated with the GTN-650 and/or a noisy LED NAV/Strobe. Does the problem go away if you turn off the LED lights? If you cannot receive VOR stations at a reasonable range, then I’d suspect the antenna install.

Just slapping in an Archer antenna can be hit or miss. Find a ham radio guy with a real antenna analyzer to ring out your coax and the antenna. Also if using a 90 degree solder BNC connector for the nav antenna line to the GTN-650 it is real easy to short the soldered coax center pin and leave the solder joint with a little tip on it - the tip then shorts the center coax conductor to ground when you install the connector cap over the solder joint.

Carl
 
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I am able to receive a VOR about 45-50 nm around 5,000MSL. I thought that was pretty reasonable but not sure.

I did go back out and tried cycling my mag and electronic ignition. The electronic ignition is definitely putting some extra noise into the NAV signal, but even with it off was unable to hear the morse code very well. It's odd the noise is not present in the com signal. Turning the mag off did not substantially change the noise level.

I have LED nav/strobe, but already tried turning those off along with both alternators, at least on the ground. Did not try this airborne.

I'll see if someone in my local EAA chapter has an antennae analyzer
 
Did the USB outlet give you trouble even if nothing was plugged in to it? I do have one wired up along with a round type power plug.
 
I replaced my electronic ignition plugs with new BR8ES (3961) gapped at 0.25 and this has reduced the noise from my ignition. I had the screw on tips prior to this. I don't think it's ideal yet, but certainly improved.
 
I have a GMA240 audio panel. The GTN650 has the P1004 connector pins 16/17 (VOR/ILS Audio Hi/Low) wired to the audio panels pin 16/17 (NAV 1 Hi/Low).

Any other trouble shooting ideas would be appreciated.

Typo? nav audio is 17/18...
 
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