[AMPS] Re: Antenna System power ratings

[Ian White, G3SEK]

Jon Ogden wrote:
>
>>My feeling is that a PL259 should be good to 3Kw in low SWR system - say
>><2:1. Although the Type N is rated to 1 Kw, I feel unhappy about putting
>>over 4 amps through what is a BNC as far as the inside is concerned. 
>
>Agreed on the N-connectors.  I would think that a PL-259 would have a 
>higher power rating than the N due to the thickness of the conductor.  
>The center conductor of the N is really quite small and is really a BNC 
>as you say.
>
N connectors will handle high power, but only if they are in good
condition, perfectly assembled and perfectly mated. Otherwise they're
just coaxial fuses.

>I know of a company I used to call on who makes paging transmitters.  
>They had a lot of N connectors in their system that they would run at 500 
>Watts at 900 MHz.  One of the engineers told me they burned up a LOT of N 
>connectors literally and that it was one of the major field issues.  They 
>had a bunch of Ns in their system as "blind-mate" connectors (push on - 
>so they could slide modules in and out of racks. Customers don't want to 
>"screw" on cables). 

That's really asking for trouble, because assembly tolerances will
almost guarantee imperfect mating if there's nothing to pull each pair
of connectors together.

> They redesigned the system to use the 7/16 DIN 
>connectors and eliminated all of the Ns in the high power areas.
>
>I've also heard of hams burning up N's at 1500 Watts on UHF frequencies.

Yup - I recently burned one out on the 7/8" heliax on 432, so am
starting to change over to 7/16 DIN wherever possible. 

It only took 600-700W to do the damage, but it's pretty certain that
something had gone wrong inside the connector first. Probably the inner
pins had migrated apart; the RF arc-welded them permanently together,
carbonizing the Teflon in the process. 

To put all this into perspective, Ns are working just fine in other
parts of the system, including the shack end of the heliax where the
power level is higher. The emergency repair worked pretty well too,
using a straight grub-screw connector for the inner, and copper sheet
and hose clamps for the outer.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.demon.co.uk/g3sek

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