strange APRS problem

I had something strange occur on my last two flights. My APRS tracker appears to operate normally until I descend into the pattern. My radio then becomes overloaded with static and a rhythmic squeal to the point where it is painful. I know it is the micro track because the noise stops when I shut it off. This is a 300 MW unit with a twin lead antenna mounted in the right wing tip and powered off the navigation lights. In looking at my track it is obvious that I am not putting out any packets during this noisy period.

I pulled the wing tip today and inspected all connections and tested the unit on the ground and all seemed normal...

Why would this only happen below ~1500 ft and only when descending.. it doesn't happen on takeoff ??? This has happen at three different airports so it is not airport specific. Weird....

Unicom?

638RS said:

I had something strange occur on my last two flights. My APRS tracker appears to operate normally until I descend into the pattern. My radio then becomes overloaded with static and a rhythmic squeal to the point where it is painful. I know it is the micro track because the noise stops when I shut it off. This is a 300 MW unit with a twin lead antenna mounted in the right wing tip and powered off the navigation lights. In looking at my track it is obvious that I am not putting out any packets during this noisy period.

I pulled the wing tip today and inspected all connections and tested the unit on the ground and all seemed normal...

Why would this only happen below ~1500 ft and only when descending.. it doesn't happen on takeoff ??? This has happen at three different airports so it is not airport specific. Weird....

Click to expand...

Could it be associated with switching to a specific Unicom frequency?

Good point....In both cases the freq was 122.9, however I switched to the freq long before the noise started...

I'll have to investigate the freq issue further and try different airports

Something just occured to me

This problem starts after I announce my position on unicom . I wonder if my transmission puts the APRS transmitter into oscillation...

But shutting it off and turning it back on should stop it and it does not.

Things to Check.....

Hi Rich,

1) Did you glue the antenna in with Sikaflex?

2) Do you have a nosewheel?

3) Is your entire airframe primed?

4) Are you running E-mags?

Any/all of these things have been known to cause all kinds of havoc with our planes...... Sorry - I could not resist.

The unit is probably sending packets, but they are not being received when you are low in the pattern. Where is your comm antenna mounted? What comm are you running?

I have not had any issues with the J-pole and my Sl-40. If you want to try another antenna, drop me a line and Ryan and I will get you one to test.

Maybe Allen can weigh in with some thoughts.....

638RS said:

I had something strange occur on my last two flights. My APRS tracker appears to operate normally until I descend into the pattern. My radio then becomes overloaded with static and a rhythmic squeal to the point where it is painful. ...

Click to expand...

I have the same thing on one set of my noise reduction headsets. Starts sqealing on descent only into the pattern. Feedback somewhere internal to the left earphone.

Strange behavior

Let me restate the problem to make sure I understand it: A)When you tune your Comm radio to 122.900, transmit, and then descend, you start to receive an unpleasant whine in your receiver. b) The problem stops when you shut off the Micro-Trak, but starts again immediately upon powering the Micro-Trak back up. Is this correct?

Questions:

1) Are you using your ships' GPS, or an accessory hockey puck GPS receiver?
2) Does it do this with the GPS off or disconnected?
3) Do the airports you are landing on have RADAR?
4) Where are you drawing your power from?


Allen
VHS

Strange behavior

Allen,

Yes, you have described the problem correctly, other than the noise is much more than a whine, it is a loud crackling static, rhythmic in nature...

1)I am using the GPS puck supplied by Byonics
2) Don't know --- will test
3) No
4) power is drawn from the Nav light in the win tip

I forgot to mention that the unit worked normally for the first half dozen flights.

I a going to remove it from the wing tip and run it in the cockpit with 9 volt battery power to see if it still misbehaves...

Pete, Thanks for the offer of an antenna but I have another I can use to test

Interference

Please keep me advised. I am particularly interested in knowing if the MT-300 is transmitting ( red LED on) when this occurs, and if the problem occurs without a GPS connected. The Micro-Trak should pretty much be asleep between transmissions, but the GPS is always hot. If there is an undesirable product (intermediate frequency, intermodulation noise, etc) leaking in to your receiver, it seems most likely then that it is a product of the GPS. If you would like, send me your address and I will ship you a Micro-Volt. This might help bypass any noise to ground, and prevent any unforseen RF products from intruding into your Comm circuits.

Allen
VHS

Interference

Allen,

It will be a couple of days before I can test the unit. I'll keep you posted. Thanks for the input.

Problem Solved...( I think)

I removed the wing tip today to pull the micro track and test it... Which I did and it seemed to work fine on the bench with a battery power supply and a Ham transceiver to test.

However, When I removed the tip I had found that the excess cable for the GPS puck which I had secured with some Goop and a tie wrap clip in the wing tip had come loose. I don't know if this makes any sense but I have strobe power supplies mounted on the rib in each wing tip. The micro track is in the right wing tip so when I would make my turns in a left pattern it looked like the GPS wire bundle would fall on the strobe power supply and stay there. Possibly dislodging when I landed... So I relocated the GPS puck, secured the cable well, reinstalled the micro track and went for a short flight ( very bad visibility today) and all worked fine.

Further testing to be done... Thats my story and I'm sticking to it...

Strobe power supply

Interesting, and even makes sense! What kind of strobe power supply do you have?

Allen
VHS

Strobe power supply

They are Aeroflash power supplies, part number 152-0007.