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Mode C help.

RicoB

Well Known Member
Patron
Hello. I am A little puzzled. For the past month of flying I had few times when the tower said they weren't receiving my Mode C, it has happened on take off, it has happen inbound for landing. has been intermittent. My set up is Dynon D10A (has a built in encoder), GTX 327, Uvionix EchoUAT, IFD440. in the past I have cycled the transponder and tower was able to see my mode C, another times it didn't happen, another time I cycled the dynon and transponder it worked. today I took off in the morning it was fine, later in the day when I came back tower said i had no mode C, (he sees me, Ident is good, just no ALT) I tried cycling the transponder, Nothing. Tried the D10a, nothing. tried both at the same time Nothing. landed and still no mode C. i will try flying tomorrow to see if it is back alive.
Can anyone guide me how to troubleshoot this one? I was thinking of finding a 327 and swap out with mine to test it for few days. OR?
I am In KMOD for another week or so.

thanks
 
How is your D10A altitude data wired to your transponder? Is it serial (RS-232) or parallel (Gray code)? If it is gray code via a converter, there's twice the opportunity for a loose connection.

Whether its gray code or serial, I'd recommend you visually look at the wiring and each connector between your D10A and your GTX-327 to make sure they are secure.
 
I am connected via serial, D10A encoder transmit pin13 to gtx Rs-232 in- pin2

It has worked Flawless till about a month ago. Today I ran a ADSB performance report and i got to red boxes 1st is under "missing elements" - Flight ID and Baro Alt.
Both are red its the very 1st section of the report. Having a hard time figuring out if it is the D10A or the 327. I don't think the ADSB has any fault on this is also just not receiving the info i guess.

I will check the connections tomorrow.
 
I am connected via serial, D10A encoder transmit pin13 to gtx Rs-232 in- pin2

It has worked Flawless till about a month ago. Today I ran a ADSB performance report and i got to red boxes 1st is under "missing elements" - Flight ID and Baro Alt.
Both are red its the very 1st section of the report. Having a hard time figuring out if it is the D10A or the 327. I don't think the ADSB has any fault on this is also just not receiving the info i guess.

I will check the connections tomorrow.

If I’m not mistaking, the uAvionics Echo gets its altitude information from the transponder so either your transponder itself is intermittent or the Dynon encoder is intermittent, probably due to a poor electrical connection somewhere. If the transponder interrogation reply indicator in on when this is happening, my bet is on problem with it not receiving the encoder information consistently.


Skylor
 
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Rico, definitely check that 327. I just worked through a friends issue with a new GDL 82 install with the same unit. It was a failed transponder and had to be factory repaired. It also has a software update you might need, so check the version number. I don't recall precisely the version needed, but it did relate to an altitude issue with the ADSB pickup.

So, check your transponder and sw version. Serial altitude is recommended as precision is higher than gray code.
 
Does the xpdr display altitude data when the mode c is inop?
I assume it is losing that data from the dynon/wiring as I've never seen one display altitude but not transmit the data.
 
Echo app

What does echo app show while on ground? If you can get a interrogation blip on transponder, check the EchoUAT app on your phone and see if you show squawk 1200, pressure and gps altitudes. Should see all three. EchoUAT gets its data for altitude and squawk after transponder receives and transmits it out by sniffing micro voltage on plane wiring of this transmitted data. If not seeing data, drop sensitivity on EchoUAT lower....lower means increased sensitivity. Good luck.
 
If I?m not mistaking, the uAvionics Echo gets its altitude information from the transponder so either your transponder itself is intermittent or the Dynon encoder is intermittent, probably due to a poor electrical connection somewhere. If the transponder interrogation reply indicator in on when this is happening, my bet is on problem with it not receiving the encoder information consistently.


Skylor

Skylor, thanks for the reply.

I will inspect the plug integrity and connection.
 
Rico, definitely check that 327. I just worked through a friends issue with a new GDL 82 install with the same unit. It was a failed transponder and had to be factory repaired. It also has a software update you might need, so check the version number. I don't recall precisely the version needed, but it did relate to an altitude issue with the ADSB pickup.

So, check your transponder and sw version. Serial altitude is recommended as precision is higher than gray code.

Hello Bill.
I am hopping that this issue is the transponder. I am trying to locate one around Modesto that I can input my same settings and do couple of test flights. That would be the easiest way to rule out the transponder. I will check the SW version. I am connected via serial.
 
Does the xpdr display altitude data when the mode c is inop?
I assume it is losing that data from the dynon/wiring as I've never seen one display altitude but not transmit the data.

Is there any way to check if the dynon is sending the ALT info? specially when they report not getting my Mode C?
 
What does echo app show while on ground? If you can get a interrogation blip on transponder, check the EchoUAT app on your phone and see if you show squawk 1200, pressure and gps altitudes. Should see all three. EchoUAT gets its data for altitude and squawk after transponder receives and transmits it out by sniffing micro voltage on plane wiring of this transmitted data. If not seeing data, drop sensitivity on EchoUAT lower....lower means increased sensitivity. Good luck.

Hey Butch,
I have not checked the ECHO App. i will check it today. Dropping the sensitivity you mean getting into the hidden menu and lowering the threshold setting?
 
You should be able to verify your pressure altitude on the 327 display while in Mode C . That may tell you about the ability of the 327 to receive the serial or grey code altitude from the D10. The next level would be to check on your phone echo app and see if the 327 is TRANSMITTING the altitude and that the ADSB data is being received by the echo. I would verify these before swapping out 327 . best of luck
 
You should be able to verify your pressure altitude on the 327 display while in Mode C . That may tell you about the ability of the 327 to receive the serial or grey code altitude from the D10. The next level would be to check on your phone echo app and see if the 327 is TRANSMITTING the altitude and that the ADSB data is being received by the echo. I would verify these before swapping out 327 . best of luck

Hello Dennis.
So yesterday when tower couldn't see my ALT the transponder was displaying the pressure alt, i was reporting my alt to the tower by it. than I rebooted, it showed the pressure alt right away on it's display but no joy for the tower, for a brief moment the was dashed lines on the transponder (10 sec or so) but it came back on my display but not on the tower. I will try to fly today and see if happens, if so i will open up the echo app to see if it is feeding to it.
 
Does the xpdr display altitude data when the mode c is inop?
I assume it is losing that data from the dynon/wiring as I've never seen one display altitude but not transmit the data.

Walt, This will validate the transponder is getting the altitude, but not necessarily reporting with the ADSB output. The transponder I was referring to (GTX327) had an accurate readout of altitude on the display but not in the adsb report. Precisely, the adsb altitude report was periodically blank. As noted, it was a transponder issue due to triggering from the ADSB unit to meet the ADSB report cycle. It is a longer story, but that is the short version.
 
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Hi Rico, look at section 5.2.9 of the 327?s installation manual. There?s a page you can bring up that lets you view the serial data input to the 327.
 
Make sure the transponder is seating correctly/fully in the rack. I had a transponder problem in an older airplane, with similar "no mode C" issues, and bumping the face of the transponder with the palm of my hand resolved the issue. It just needed to be tightened down.
 
Clean Antenna

Also, be sure your transponder antenna isn?t dirty. I have heard of engine oil on the antenna causing issues with signal transmission.

Skylor
 
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