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Triaxial Cable, What For? - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


Lipari
 Post subject: Triaxial cable, what for?
Posted: Mon Feb 23, 2009 1:27 pm 
 
Lieutenant

Joined: Mon Feb 23, 2009 1:06 pm
Posts: 1
Hi everyone,

I’m working on a project involving antenna installations on a navy ship. The specifications call for using triaxial antenna cable, i.e. coaxial cable with two separate AND insulated shields.

I’ve done a lot of antenna installations in many sorts of environments and normally I use double braided cable like RG-214 or foil+braid cable. This normally satisfies all requirements for shielding as foil+braid cable has a shielding efficiency of around -90dB.

I’ve been searching the internet for more knowledge, and I’ve found some manufacturers like Times that makes triaxial cable and others like Trompeter and King that makes connectors.

The cable specs are not so impressive, they seem to be equivalent to the foil and braid double shielded coax. The pricing is however very impressive ;-). Also the connectors look very expensive.

So what are the true benefits of using triax for HF and VHF shipborne antennas? Has it got something to do with EMP protection levels?

I would appreciate any input on this from someone more knowledgeable then I.


 
   
 
nubbage
 Post subject: Re: Triaxial cable, what for?
Posted: Sat Feb 28, 2009 5:00 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 236
Location: London UK
Hi Lipari
we often use double-screened coaxials in the oil/gas industry on off-shore platforms, in the sense that a regular RG-214 with a braid-armouring jacket around the PVC outer sheath of the regular RG-214 is pretty well what you describe.
There are 3 reasons this is done
1. for additional mechanical strength in a tough outdoor environment
2. Differential grounding: the armouring is grounded to any steelwork, while the inner breaid is grounded to a low-noise low resistance earth to the bottom of the vessel and the sea.
3. It affords better lightning strike protection as the armouring can be grounded outside a steel room, passed through a wall transit with just the regular coax (having stripped the armouring away) then the cable terminates at the equipment end as usual.

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