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Transponder Antenna Question?

Piper J3

Well Known Member
I have a Garmin 327 Transponder in my RV-12. I?m having a problem with uAvionix echoUAT ?sniffing? Baro Alt. My PAPR shows 100% fail for Baro Alt. I?ve been working with Kurt at uAvionix and they sent me a new echoUAT and it also fails Baro Alt.

I?m beginning to think I have a transponder problem. Transponder is set for 1200 ALT and displays pressure altitude. I can see steady pinging from ATC on the transponder so I think transponder is working. Transponder was certified one year ago.

Here?s my question? I notice the transponder antenna is loose ? the stem with the ball tip is able to be rotated in the mounting base. I assume the stem is connected to the center wire of the coax and it must be disconnected. I?m hoping this is the problem.

1) Do you think the Transponder is damaged because of no-load on the antenna?
2) Van?s show the part number for the antenna as AV-22. I look this PN up on Aircraft Spruce and see various Transponder antennas listed at different price points. Is there a difference in antennas? AV-11, AV-22, TED, CI 101.
 
Just go fly, and call up ATC and ask if they see your transponder. Then you'll know.
But all of these "sniffer" ADSB units have a means of adjusting the sensitivity for the transponder pick up, to account for antenna spacings, etc. Read the manual, or call uAvionics.
 
Just go fly, and call up ATC and ask if they see your transponder. Then you'll know.
But all of these "sniffer" ADSB units have a means of adjusting the sensitivity for the transponder pick up, to account for antenna spacings, etc. Read the manual, or call uAvionics.

Yes, uAvionix has had me change Transponder Monitor Threshold value to no avail so that is why I suspect transponder problem.
 
I believe it’s normal for the ball to be able to rotate.

If it's a TED antenna, the ball is fused to the rod (press fit, I believe) and the rod is soldered into the base. If it rotates, it is likely bad and likely the reason for your poor transmission performance. I have successfully repaired them by re-soldering the base with silver solder, but the insulator must come off first.

Receiving queries from the base station is not an indication of optimum performance. A bad antenna will lose more performance on transmit, as the ground stations are cranking out stronger signals.

Also, Uavionix has a serial mux that will avoid the sniffer for use with a 327. It gets the data from the serial port. The mux digitally branches the RS-232 feed for use by Echo

Larry
 
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Uavionix has a serial mux that will avoid the sniffer for use with a 327.
Could you elaborate on that, please. My RV-12 buddy is in the process of installing a Uavionix right now and would hate to remove his wing a second time to run a serial cable.
 
Food for thought

I had exactly the same experience when trouble shooting a bad TXP on my RV12 a few years back. It passed a ground TXP check, but was weak. I noticed that I was only occasionally seeing interrogations on the TXP screen.
I checked the antenna and found the same thing as you, a rotating post, so I changed to a new antenna, to no avail.
Finally, I tested the cable from the TXP to the antenna and the BNC at the antenna side ended up being bad. (This was a factory cable and it may have been like this from the beginning but only noticed when I started flying into controlled air space.)
I was back in business after putting on a new BNC. Interrogations were up to one or two per minute and it passed the TXP test with no problems. By the way, I changed back to the old antenna just to verify that it was good and it works fine even though you can still rotate the stem; however, this may not be the case in every situation.
Just another place to check.
By the way, I have this same ADS-B set up in my RV3, with the GTX327, and it works fine with no issues sniffing the TXP.
Good luck.
 
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Update... I flew today in loose formation with a friend's plane. He saw my tail number on his ADS-B traffic screen. I also called ATC and asked for transponder check - they had me squawk code and saw me as target with correct encoded altitude. So, transponder is working fine even with loose AV-22 antenna. I have ordered new antenna and will install soonest.

Now back to original problem where echoUAT is not sniffing encoded altitude from the transponder. I will call uAvionix on Monday to discuss.
 
Also, Uavionix has a serial mux that will avoid the sniffer for use with a 327. It gets the data from the serial port.
Yes, this is a great solution. Just order this harness when you call the uAvionix rep. It's as simple as one more connection while you're under the panel.

It's called the echoUATmux harness.
 
Jim,

What range of threshold settings have you tried? I had to go all the way down to 1350, and I have heard of some people needing to go even lower to get reliable results.
 
Jim,

What range of threshold settings have you tried? I had to go all the way down to 1350, and I have heard of some people needing to go even lower to get reliable results.

See table below.



uAvionix sent me a MUX cable - see photo below. Instructions that came with cable are anything but clear. My echoUAT transceiver is mounted in the baggage compartment. This cable harness doesn't look correct with three separate connectors?

navigate to nearest fuel station

I think correct wiring for GTX327 to echoUAT is this...




I have emailed uAvionix and haven't heard back yet. My guess is they are busy with run-up to OSH and 2020 just around the corner.
 
The Monitor and Configuration screens are different for the echoUAT but act similarly. I have used the Monitor screen on each flight and always see Pressure Altitude reported. Its a big mystery as to why I keep failing for some % Baro Alt.

History - I installed echoUAT last August and it worked fine with dozens of passed PAPR. Then I noticed (as did others) that targets were disappearing on screen. I tried to install new uAvionics software that solves this problem but my echo gave message that it would not accept software update. uAvionix sent me a new echoUAT and that is when my Baro Alt troubles all began. I have been struggling since November to pass PAPR.
 
I have been struggling since November to pass PAPR.
That's frustrating. I'm sorry you're having problems with the EchoUAT. It sounds like Uavionics hasn't quite gotten all the bugs out yet. (I went with the GDL-82 and have had zero problems.) I did need to install a new broadband (blade type) transponder antenna, though. I bought a Delta-Pop antenna.
 
It took several emails back/forth but I finally understand the wiring for the MUX cable. See wiring diagram below...

 
Failed PAPR for 1.66% Baro Alt

I have echoUAT with SKYFXY-EXT and Garmin 327. As described in my posts above I have the SKYFXY-EXT wired directly to the echo and now have the altitude encoder wired to pins 1 & 3 on a MUX cable. I couldn?t get the echo to sniff the transponder reliably so I added the MUX. I?ve been flying this new configuration now for over a month with good PAPR?S until today where I failed for Baro Alt = 1.66%. I go back and look at previous PAPR?s and see all have a low incidence of Baro Alt % (all below 1.5% except for today = 1.66%).

I?m wondering if I have an incorrect parameter setting in my transponder or wrong baud rate set in the echo. Transponder passed VFR certification 12 months ago.

Any thoughts/suggestions appreciated?
 
I'm going to fly one more flight tomorrow to get another data point and then talk to uAvionix at Oshkosh on Thursday.

I wonder if FAA has folks at Oshkosh to help understand ADS-B implementation problems?
 
Did you try or ensure the ground for the Beacon runs to the forest of tabs main ground?

Instructions mention this as a possible need.
 
I talked with FAA ADS-B specialist last week at Oshkosh AirVenture and they analyzed several of my past flights for failed PAPR. The flights show intermittent Baro Alt throughout the flight regime. The FAA provided two data files and suggested that uAvionix could help me determine how to troubleshoot the problem. I'm waiting for response from uAvionix. Does anyone have idea on how to troubleshoot this?

I can provide FAA data files by email request.

Any assistance will be appreciated…



 
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Baro Bad?

Jim, This a a little out of the box thinking but, your baro is from another pin of the transponder. In other words it comes from the processor to the output.
May be overloaded from a mass of traffic, TCAS, so on, etc, and can't send the data all the time to the avionix.....

Also, you have pin 20 and pin 19(GAR 327), both, in the same shielded cable..a no no. Probably not the problem, can be crosstalk though.

RS232 specs don't allow this but, I would tie the output of the encoder to
the avionix input and the 327 (pin 19) together, as a test. If it works
then the 327 is "slow". This is not a fix, just a test, only a test.

If it works........?.... I have the patch....

John
 
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