Transponder not working - how do I troubleshoot?

[Bill_H]

I have a new RV-12 with Skyview and Dynon transponder. I am flying off the initial hours. I live in an area with really poor radar coverage (northern Arkansas.)

On a test flight yesterday, I climbed to 8000' and ATC was still not getting a transponder signal, although they were getting a primary return.

I am getting no diagnostic messages from the transponder. The code is showing in the top bar, in green, showing ALT. I was able to change codes and Ident and the Ident indicator shows up. ATC did not receive the Ident. I cycled it to OFF and ON and ALT with no change in ATCs reception. The Reply Status indicator never appeared during the test.

(I HAVE registered the transponder with the Octal code as per Chapter 11 in the installation manual. Hex A4DBB7 to Octal 51155667. If that was wrong would it cause this?)

How do I troubleshoot this? Obviously I will check the antenna connections but would a faulty connection produce some sort of error message? How would I best check the antenna connections?

 

[dynonsupport]

A transponder and altitude encoder must be checked by a shop before your first flight and every few years. They will verify all the antenna connections and the overall performance of the system. They will verify that the transponder replies correctly and at the right levels. Has this check been performed?

 

[Bill_H]

No such check has been performed and indeed the Skyview installation manual states specifically how the FAA 24-month check is inapplicable to this transponder since the altitude source is identical for the EFIS and the transponder. There were no requirements for an avionics shop check of the transponder in the RV-12 installation instructions.

 

[Bill_H]

In any case, the question remains - how do I best troubleshoot it myself - at least initially? I don't want to fly to an avionics shop, then pay a fee for them to tell me perhaps "The box is bad. Get another one. Put it in, bring it back, and we'll check it again and you can pay another fee." I'd like to do as much as is possible myself, lacking radio test equipment.

 

[dynonsupport]

There is no way to test it without RF test equipment. It's a TSO'd device that worked when tested at the factory. The serial communications to and from it are working, so the whole box is not dead. It is allowing you to go into ALT mode, so the self test has been passed and it thinks it's fine.

There is a 99% chance that the issue is in the RF cable or antenna, since the transponder is acting like there is no antenna installed. It's worth checking your cable for crimps, shorts, breaks, etc, and to make sure it has a solid connection to the antenna and the ground plane for the antenna.

After that though, the only way you can "test" it is to mess with it and then go fly it again and see if it works, but that's 100% illegal if it has not been checked by a certified test station.

The transponder is the only device in a homebuilt that must be certified and tested. Please don't give the FAA reason to put more regulations on homebuilts by ignoring the one, single requirement they have.

Sorry for the harsh tone, but as vendors of a TSO'd transponder, we cannot condone any use of the transponder in an improper manner, and implore you to get it tested properly.

 

[DonFromTX]

So, is this statement correct in regards to an EAB aircraft?

A transponder and altitude encoder must be checked by a shop before your first flight and every few years.

 

[Bill_H]

I am not currently flying in airspace that even requires a transponder.

 

[dynonsupport]

So the statement about the altitude encoder calibration is really aimed at 91.217(2) (see http://www.risingup.com/fars/view_far.php?part=91&type=FAR&num=217), which says

...Unless, as installed, that equipment was tested and calibrated to transmit altitude data corresponding within 125 feet (on a 95 percent probability basis) of the indicated or calibrated datum of the altimeter normally used to maintain flight altitude, with that altimeter referenced to 29.92 inches of mercury for altitudes from sea level to the maximum operating altitude of the aircraft; or...

So what we're saying in our manual is that these devices are one and the same. Therefore, the altimeter and encoder are within 0 feet of each other 100% of the time by definition, which satisfies the above test requirement.

Now, separate from that, you need to comply with 91.413 (http://www.risingup.com/fars/view_far.php?part=91&type=FAR&num=413), which says:

....No persons may use an ATC transponder that is specified in 91.215(a), 121.345(c), or §135.143(c) of this chapter unless, within the preceding 24 calendar months, the ATC transponder has been tested and inspected and found to comply with appendix F of part 43 of this chapter; and....

The above basically means that you can't use your transponder in any controlled airspace, you need to test the end to end system. We don't make any claims that this requirement is alleviated.

 

[dynonsupport]

To be clear: 91.413 is a regulation that applies to all pilots in all aircraft in the USA, so it does apply to EAB aircraft.

You can fly the plane before you get the transponder certified, as long as you don't turn it on, which means you are fine in areas that do not require a transponder.

 

[Bruno]

Hello Support
        Just for my own education on the subject above...

Will it be possible that the Dynon TXPR will show on the Skyview display ( Direct wiring to the DB-37 HARNESS) and while not properly setup as part of the serial port set up in the set up menu..

I know in my case, my Garmin GTX-327 was showing up on the display and ATC were getting a primary return but no altitude return but when I checked the Port set up, it wasn,t set up the right way ( I believe the encoder part was set up to NONE while it should have been set to ICARUS 100 or 10 ..Once I done the change ,ATC were able to see the altitude returns...

It might be worth a look/see..

Bruno

 

[Bill_H]

Problem probably found!

I have a defective transponder antenna cable. This is the RV-12 SKYVIEW update "adapter" cable- a short 11 inch cable is supplied to adapt from the Dynon transponder component antenna connector (which has a female center pin and male threads and is non-BNC) to the existing BNC cable already run in the plane to the antenna.

This adapter cable center pin is shorted to the connection hardware on both ends. This explains my problems in that the Dynon transponder's self-diagnostics are fine but it does not receive ATC interrogations nor transmit responses.

It is labeled "Coleman Cable, 988591, M17/28-RG058 MIL-DTL-17 OXDS2" - Since all parts for us RV-12 builders come from Van's, I am not sure if this adapter cable is supplied by Van's, Steinair, or Dynon.

The cable has a male-pin/female threaded connector combo on one end and a female-pin BNC connector on the other, 11 inches long.

The short in it is a pretty good one, it does not alter if you bend or move the cable around. I checked the other existing cable to the antenna and the antenna itself and they are fine - the center pin conducter is isolated from ground and the antenna and cable itself is well grounded to the airframe.

In checking everything out, I have another question. Having removed the antenna cable from the transponder component itself, I checked for continuity between the center pin of the connector on the transponder component to aircraft ground and to the connector body around that center pin. There WAS continuity with both the DB cable connector in place or removed. Now, this is kind of back-checking circuitry inside the transponder box itself, but I am wondering if this is a normal indication. Thanks - Bill H.

 

[dynonsupport]

RV-4: No. If the transponder isn't assigned to a serial port, the transponder window and menu won't even appear. If it's hooked up to our transponder but, say, you've chosen the wrong serial port in the setup, you'll get a "red X" and a transponder failure warning message in the message alert area / window. For 3rd party transponders, we can only display the status they provide. Note that a 327/330 display pressure altitude on their own displays.

Bill: In short - on the antenna side of things, we don't sell or provide anything downstream of the transponder itself. On the D25 side, the transponder comes with D-sub shell, connector, and pins, but a "retail" customer would make their own harness for that. With the RV-12, of course, you get more than that from Vans.

 

[Bruno]

Hello Support

Thanks for the info

Cheers

Bruno

 

[TRCsmith]

Just a note on transponders, You also are required to have a transponder anytime you're above Class "C" airspace and above 10,000 MSL. 

For those that fly away from B airspace but near C.