Did surefly kill my transponder?

[Derrickearly]

I just had a surefly installed in my M20F. Now, my gtx345 is not transmitting. Did I just get lucky, or is the surefly causing some interference with the transponder?

Update:  A new transponder antenna resolved the issue. 

Edited June 17, 2024 by Derrickearly
Fixed issue

[Red Leader]

Unaware of any interference caused by the addition of a SureFly but more likely you will find it is a wiring/connection issue caused by others fumbling behind the panel or engine bay that might've caused this issue. Take it back to the mechanic that installed the device and find a diplomatic way to inquire if it might've been something done during installation to cause the trouble. 

[Derrickearly]

1 minute ago, Red Leader said:

Unaware of any interference caused by the addition of a SureFly but more likely you will find it is a wiring/connection issue caused by others fumbling behind the panel or engine bay that might've caused this issue. Take it back to the mechanic that installed the device and find a diplomatic way to inquire if it might've been something done during installation to cause the trouble. 

It’s already with him. We’re going to try a new antenna tomorrow. 

[Red Leader]

Been there, done that. Don't let them say it's the antenna (which might fix the issue) when all it could be is a connection that is fixed when installing a new antenna. They LOVE to bill for solving problems which they might have caused. It allows them to make more money and helps them save face - you, otherwise, would never know.

[Derrickearly]

5 minutes ago, Red Leader said:

Been there, done that. Don't let them say it's the antenna (which might fix the issue) when all it could be is a connection that is fixed when installing a new antenna. They LOVE to bill for solving problems which they might have caused. It allows them to make more money and helps them save face - you, otherwise, would never know.

I trust Chris. We have already tried the simple stuff. 

[PT20J]

Any chance the GTX was powered up with the antenna disconnected? Running the GTX without the antenna (or a dummy load) connected can damage the power stage because it transmits Mode S acquisition squitter pulses once a second even if not receiving ground radar interrogations and with no antenna all the energy gets reflected back into the transmitter. This problem most often occurs during maintenance when a belly panel is removed and the antenna is then disconnected. My installer put a label on the coax at the antenna end reminding to pull the GTX circuit breaker if the antenna is disconnected.

There is a caution about this in the GTX maintenance manual.

[PeteMc]

33 minutes ago, PT20J said:

Running the GTX without the antenna (or a dummy load) connected can damage the power stage because it transmits Mode S acquisition squitter pulses once a second even if not receiving ground radar interrogations and with no antenna all the energy gets reflected back into the transmitter.

Good advice for ANY transmitter.  Just DO NOT transmit without an antenna or dummy load.

 

[Derrickearly]

4 hours ago, PT20J said:

Any chance the GTX was powered up with the antenna disconnected? Running the GTX without the antenna (or a dummy load) connected can damage the power stage because it transmits Mode S acquisition squitter pulses once a second even if not receiving ground radar interrogations and with no antenna all the energy gets reflected back into the transmitter. This problem most often occurs during maintenance when a belly panel is removed and the antenna is then disconnected. My installer put a label on the coax at the antenna end reminding to pull the GTX circuit breaker if the antenna is disconnected.

There is a caution about this in the GTX maintenance manual.

Maybe a failed antenna could kill my transponder. We never operated it without the antenna connected. 

[MikeOH]

1 hour ago, Derrickearly said:

Maybe a failed antenna could kill my transponder. We never operated it without the antenna connected. 

Maybe, but I’m just not a big believer in coincidence: working fine before the shop laid hands on, not working after….sorry, my bet is the shop is responsible.

I get it that you may have to go-along to get-along if you want to keep a good relationship with the shop. Hopefully, they “deep discount” the antenna, or whatever, they say is broken.

[PT20J]

Did they run a VSWR test on the antenna and cable, or are they just replacing it? Antennas are pretty simple devices. Not really a lot to go wrong and hard to see how it would kill the transmitter unless it was physically damaged causing a short or something. But @EricJ's likely more knowledgeable about antennas.

[EricJ]

+1 that actual antenna failures are extremely rare.   Sudden cable failures are also rare unless suddenly crimped or cut or stretched or such.   Something got bumped or dislocated or disconnected or something.   

If you let them sell you a new antenna, KEEP THE OLD ONE, because it is almost certainly still good unless it is physically broken.

They're easy to test, including the cable or not, with appropriate equipment.

[dkkim73]

Tangential question: would the above caution about transmitting without a dummy load or antenna mean that one should not turn on the master/avionics (tied in my plane, G1000) when the belly panel is dropped without attaching the xponder cable to a dummy load?

[EricJ]

1 hour ago, dkkim73 said:

Tangential question: would the above caution about transmitting without a dummy load or antenna mean that one should not turn on the master/avionics (tied in my plane, G1000) when the belly panel is dropped without attaching the xponder cable to a dummy load?

You don't want the transponder to transmit without a load, so if it doesn't come on unless the avionics bus is on, that's one safety.    You can also turn it off or pull the breaker to keep it from transmitting.    Ground mode may work, but I don't trust it. 

Many of the more modern transmitter designs include input protection for the power amplifier, so this is not an issue for them, but unless you know that a particular device has that it's best to be careful.

 

[Fly Boomer]

1 hour ago, dkkim73 said:

Tangential question: would the above caution about transmitting without a dummy load or antenna mean that one should not turn on the master/avionics (tied in my plane, G1000) when the belly panel is dropped without attaching the xponder cable to a dummy load?

I was confused by this question.  I don't know anything about your airplane, but on my M20K, the transponder antenna isn't attached to the belly panel -- it's on the bottom of the fuselage further forward.

[dkkim73]

1 hour ago, Fly Boomer said:

I was confused by this question.  I don't know anything about your airplane, but on my M20K, the transponder antenna isn't attached to the belly panel -- it's on the bottom of the fuselage further forward.

The transponder "baby shark fin" is on the aft ventral panel on the M20TN. Sorry, I did not think to clarify this as I thought it was a common mounting position. 

[Derrickearly]

The new replacement rod antenna resolved my transponder issue. The old one was bent previously, so I guess that damage caught up with me.