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Correct coax for GTX-327 antenna

Simon Hitchen

Simon Hitchen

Well Known Member
Just wondered if anyone could shed some light on the Coax people are using for the antenna on the transponder. The manual States rg400 is ok with a max length of 8.8 feet. My installation routing exceeds that yet I'm finding it a challenge to find the next recommended coax of RG304 in anything less that 100 foot spools.

Many thanks
 
A better solution would be to relocate the antenna closer to the transponder. The 327 is a great unit but typically it does not have much power to spare. Any more than the specified 1.5 db cable loss and you risk not being able to pass the req'd biannual transponder test.

Another option (not as good as moving the antenna closer) would be to use solid core RG142 which is pretty common and has a little less attenuation than the RG400 (12.8db vs 14.7db/100 ft) is the same size and uses the same connectors as RG400, this would allow you about 10ft vs 8.8ft.
 
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Walt said:
A better solution would be to relocate the antenna closer to the transponder. The 327 is a great unit but typically it does not have much power to spare. Any more than the specified 1.5 db cable loss and you risk not being able to pass the req'd biannual transponder test.
Click to expand...

FWIW I had the same situation with my transponder installation and always had issues with ATC not seeing my transponder from any significant distance. When I installed a new panel, I relocated the transponder module a lot closer to the antenna (from 15ft to 4ft) and all the issues went away.

:cool:
 
Been there

Installed RG304 when my install was around 10 feet. Hard to find and was somewhat difficult to get connectors. It is also a FAT cable to run through the center section. Did it just in case the margin was needed for the new Mode S stuff at a later date.
Using RG304 I have never had a complaint from ATC :)

If I was to do it today I would get a remote transponder like the trig to keep the coax run to a minimum.
 
Walt, the electrical gurus always say to never use solid core wire in airplanes and boats (basically anything that moves) due to the vibrations and possibility of breaking. Has this changed??? Inquiring minds want to know!:)


Walt said:
A better solution would be to relocate the antenna closer to the transponder. The 327 is a great unit but typically it does not have much power to spare. Any more than the specified 1.5 db cable loss and you risk not being able to pass the req'd biannual transponder test.

Another option (not as good as moving the antenna closer) would be to use solid core RG142 which is pretty common and has a little less attenuation than the RG400 (12.8db vs 14.7db/100 ft) is the same size and uses the same connectors as RG400, this would allow you about 10ft vs 8.8ft.
Click to expand...
 
JDanno said:
Walt, the electrical gurus always say to never use solid core wire in airplanes and boats (basically anything that moves) due to the vibrations and possibility of breaking. Has this changed??? Inquiring minds want to know!:)
Click to expand...

Which internet electrical Gurus are you referring to? Both are MIL-C-17 approved cables and both are used extensively in aircraft.
For example Garmin (and many others) call out 3C142B coax (or something similar) in their approved install manuals, this cable is basically RG142 made by ECS and Carlisle.
 
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Thank you

Thanks everyone, I managed to get the cable length down to 10 feet and the experts seem to feel that regular RG400 will be just fine.

Thanks for the help
 
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