261 Transponder vs. Garmin 327

[rdowens]

I upgraded to the Dynon transponder (261) and have the ADS-B receiver. All seems to be working reasonably well; however, in more remote areas, the transponder signal seems to disappear from ATC whereas the Garmin 327 did not.

The installation is exactly the same (antenna and ground plane). The physical location of the new transponder is slightly closer to the antenna / ground plane, and the antenna wire needed the TNC connector instead of the BNC. I shortened the existing antenna wire maybe 8 inches and installed the TNC. Otherwise, all is the same.

The ADS-B receiver and antenna are about 2 feet away.

Should the signal strength be the same between the Trig unit and the Garmin unit? If it's installation, the only thing I can think that might be reasonable to blame is the new TNC connector.

Any ideas?

Thanks,

-Randy

 

[dynonsupport]

Well, first, what does your shop say? Since you put a new transponder in, you need a new transponder certification (assuming you are in the USA at least), and one of the tests is for output power. This would be the first thing I would check. The whole reason this is required is in case things like a cable are crimped improperly.

The -261 transponder is 250W nominal while the 327 is 200W nominal, so the -261 should work at pretty equivalent distances. However, frequency tolerance, sensitivity of the receiver, and other things come into play. The -261 is a Mode S while the 327 is a Mode C so for all I honestly know, the ground radar may treat them very differently. I know that Mode S and Mode C are processed differently so it could be that the ground processing allows a Mode C to "coast" farther than a Mode S.

How are you determining range? You are asking ATC if they can see you and they now can't see you in a place and altitude where they could see you reliably before?

 

[TRCsmith]

"Well, first, what does your shop say? Since you put a new transponder in, you need a new transponder certification (assuming you are in the USA at least), and one of the tests is for output power."

I hear more about problems with transponders lately. Why? because people are violating the FAR's.

FAR 91.217 requires that all transponder-equipped aircraft have their altimeter and encoder checked for data correspondence after initial installation or subsequent modification.

Also read FAR 91.413 - ATC transponder tests and inspections.

Note: Part 91 of the Federal Aviation Regulations also apply to Experimental Aircraft. 

If the transponder check was done, you would know if it was working correctly and what to fix if not. Just because it's a homebuild doesn't allow you to install a transponder and go fly. It MUST be check be a A certificated repair station properly equipped to perform those functions, 99% of homebuilders are not certified to do this inspection.

You must have an endorsement entered into the aircraft log book showing the check was completed and by what repair station. The check cost from $40 to $80.

 

[rdowens]

Thanks guys!

I had the transponder checked prior and it was A-OK. I just thought I would ask since I noticed a difference from ATC.

-Randy