TX POWER LOW (145)

[Jerry Gaulden]

Flying a first-generation Van's RV-12 with Dynon Skyview Classic and associated transponder. The avionics kit was purchased from Van's Aircraft in late 2011 or early 2012. During flight, I'm getting the following transponder error message:

TX POWER LOW (145)

Can you please assist by telling me where to start troubleshooting?

Thank you!

 

[MikeD]

Transponder errors are listed in the Skyview installation manual. Get a copy of the Skyview Installation manual that is appropriate for your model.

From the manual:

TX POWER LOW (value)

Transmit power output is low;
value is Power output.

Generally, an installation issue
with antenna, feedline, or
connector. Check antenna,
feedline, or connector. A visual
inspection is often not sufficient
to find the fault.

Good luck troubleshooting!

 

[Rhino]

Is this a new install or a new problem on equipment that was previously installed? If a new install, I'd suspect the cable and/or connectors. For an existing install, I'd add the antenna as a possible culprit. They can be bad out of the box, but mostly tend to have faults with age. Make sure good quality cable was used, not the cheap RG-58 stuff. RG-400 or better is recommended. Make sure there is no shorting of pins, pushed pins or bad solder joints on the connectors. Bad solder joints have a habit of showing up over time rather than just being obvious in the beginning. And don't forget to check for plain old loose connectors.

 

[Jerry Gaulden]

To answer your first question, this is an old problem on equipment that was previously installed. In other words, the system was installed in 2012 and has never worked properly. Please don't ask. The SV-XPNDR-261 has a TNC connector for the output cable. There is a short cable approximately eight inches long that serves as an adapter from TNC to BNC. From there, it's BNC through to the antenna.

An interesting observation: there is electrical continuity between the center pin receiver and threaded barrel on the TNC connector on the SV-XNDR-261 itself. Is this to be expected? I hope I'm using the correct terminology here.

It seems to me that I could install the Amphenol 242149 BNC Jack to TNC Plug at the SV-SPNDR-261, replacing the existing adapter cable. Then install a new BNC cable to the antennae. For good measure, it might pay to go ahead and install a new antenna while I'm at it.

Your opinion here will be greatly appreciated.

 

[Rhino]

Continuity would depend on several factors. Are you measuring the cable at the transponder end, or the connector on the transponder itself? I'm not sure about the 261, but some continuity on the cable and antenna may be perfectly normal, depending on the type of antenna used. The type of cable can also affect that, and your TNC to BNC adapter can too. Quite a few variables at play there.

If it were me, and I realize you're not me, I'd get rid of the TNC to BNC adapter and just build a straight RG400 cable with TNC on one end and BNC on the other. That's the least expensive option for eliminating several possible culprits. Next, I would replace the antenna. If you decide to replace both cable and antenna at the same time, you could also consider an antenna with a TNC connector if you can find one that works for you, but that isn't really necessary. Before I did any of this though, I'd contact Dynon to make sure there aren't any known issues with the 261 that might be causing this.

 

[Rhino]

By the way, there are places out there that will custom make that cable to your desired length if you don't want to do it yourself, and they'll test it before sending it to you.

 

[GKC Aviation]

I had a BNC 90 degree adapter do this to me recently with a new Garmin GTX345 installation.
The GTX was brand new, new antenna cable, and the adapter was brand new out of the packet. It caused a 1030Mhz receive fail.
Process of elimination revealed the adapter was at fault. It wasn't a cheapo one either, Amphenol.
Weird things happen at high frequencies sometimes.
Making up a new RG400 antenna cable is a simple quick job, someone will be able to do it for you for the cost of materials and a 6 pack

 

[Rhino]

....Making up a new RG400 antenna cable is a simple quick job, someone will be able to do it for you for the cost of materials and a 6 pack

Relatively speaking, yes. But I learned long ago that things most of us avionics/electronics consider quick and easy, are not necessarily so for everyone else. I saw some people get transitioned to new careers because, even after passing more than a year of electronics training with great scores, they still couldn't solder correctly, even if their life depended on it. Strangely enough, coax cables seemed to be the thing that tripped them up the most. Go figure.

 

[GKC Aviation]

they still couldn't solder correctly, even if their life depended on it. Strangely enough, coax cables seemed to be the thing that tripped them up the most. Go figure.

Oh yes, I've seen some wonderful examples over the years.
I was particularly referring to getting someone that knew what they were doing to make the cable

 

[Rhino]

I know. That was more like thinking out loud, especially since I knew you could relate.