RG58 or RG400 for transponder antenna

[cscotthendry]

I guess the answer will probably be that RG400 is better, but for a short antenna cable, will RG58 be satisfactory for a transponder hookup?

 

 

[Guest Andys@coffs]

Scott

 

There's a good table in the Microair installation manual that covers this. http://www.microair.com.au/admin/uploads/documents/T2000SFLInstallationManual01R72.pdf Page 8.

 

At the end of the day it depends on the length of the run.

 

RG58U max run length 7ft (with their Tx/Rx), RG400 8ft and RG213/U is 19ft, but with a larger bend radius limitation of 125mm vs 50mm for 58 and 400. Remember that a tighter bend radius or a distortion of coax circular integrity creates a point of reflection which is counterproductive as you know.

 

Andy

 

 

[Guest Andys@coffs]

Sorry should have added, my experience is to go for the good stuff, transponders and associated wiring can create noise problems in audio systemsas you would expect from relatively sharp rise time pulses at high power....., reducing the amount of RF leakage from the transmission line helps to reduce that......a bit....

 

 

[Kyle Communications]

The RG-400 is double shielded teflon dielectric....use the RG400 The loss over the short distance is minimal

 

 

[Guest Andys@coffs]

yep about 3db loss over 5m for the RG400 (at SSR frequencies)

 

 

[Virago]

RG-400 is the only coax cable I would consider using these days. RG58 uses soft polythene type inner insulation which is prone to deformation (and melting under the right conditions). I remember tracking a transponder fault down to a length of RG58 which had been laid in the vicinity of a Cessna's hot air duct (near the bottom of the door pillar). The duct had partly come adrift from the outlet fitting allowing warm air to escape into the area behind the upholstery. The length of RG58 looked alright but a six inch section of inner insulation had melted, allowing the braid to short to the inner conductor. RG400 is more expensive and not as easy to work with but it's worth the extra expense and effort. I also recommend the use of quality crimp type BNC (and/or TNC) connectors. John

 

 

[cscotthendry]

Thanks all for your inputs and suggestions.

 

I guess the follow on question is where to source RG400 in the Brisbane area?

 

 

[Kyle Communications]

I have around 5 mtrs here how much do you need?

 

 

[cscotthendry]

I have around 5 mtrs here how much do you need?

Mark:

Not quite sure yet. I am going to install a transponder in my plane and a mate will probably need soem for his. I'm going to mount the RT under the floor and the antenna under the bottom of the tail. I'm guessing about 1.5-1.8mtr would probably do me.