[AMPS] Hi Power Connectors

[Tom Rauch]

Ian said:
> With the "UHF" the problems is manufacturing quality of the cheaper
> ones, as Ian says... so buy MIL-spec ones.

I buy my PL-259's from VanGorden Engineering in Euclid Ohio.

He sells reasonably priced teflon connectors that fit everything just 
fine. They will hold off more than 10 kW, the cable will fail long 
before the connector. 

Even regular Amphenol 259's are fine for high power, and the Van 
Gorden connectors are overkill...and less expensive. 

> With N, the manufacturing quality is generally good, but there can be big
> problems with the way we hams use them. When a loose-pin type of plug is
> fitted without a cutting jig, the pin can wind up a long way from the
> correct position, and sooner or later it will pull back or push through.

N connectors are a poor mechanical design. They do not grip the 
cable, so you have to be very careful not only in how you install 
them but in the type of cable you use.

Many types of cables have very flexible jackets. This allows the  
braid to slide on inner dielectric. The outer part of the N friction fits 
the jacket with a poor mechanical grip, and if the braid is not 
bonded or compacted into the center dielectric pushing or pulling of 
the pin is inevitable no matter how careful you are.

I've actually found premium grades of RG-8 style cables that won't 
fit UHF fittings (which screw onto the outer insulation) properly. The 
outer jacket is soft, and this prevents the braid and connector from 
staying in place. Use a cable like that on an N, and you are 
screwed! And some of those cables are expensive!

Not only does the connector not fit well, the cable will deteriorate 
rapidly for loss. That's because the braid requires compacting 
pressure to maintain electrical integrity through the weaves. 
Remember the skin effect forces current to the INSIDE surface of 
the braid, so as the wire in the braid weaves it must transfer current 
through pressure connections to the strand nearest the center of 
the cable. If the pressure is low, and the braid is free to move 
around, the electrical integrity of the strand-to-strand contact is 
quickly reduced.

I measured a sample of that cable at rated loss when new, then 
used the cable between my rotating tower and the Heliax feeding 
the system. Over a summer, without water ingress, the loss in that 
cable tripled from the flexing that loosened up the braid.

Perhaps too many people are in the connector business and cable 
manufacturing business who don't understand or don't care how 
things actually work.

Bottom line is if you are a fussy person using the proper materials, 
N's will work but not handle near the power of a good UHF 
connector. If the most simple thing messes up, from either the 
cable construction to your installation, the N will be a problem.

I guess if someone wants to use a connector that is a problem 
waiting to happen in an application that doesn't demand a constant-
impedance connection that's their choice. But they are certainly 
deluding themselves if they think it is a "better" connector for HF or 
VHF use.



  

Eve

     

> Also, we try to fit them to unsuitable cable such as 9913 where you have
> to file the inner conductor and usually get it tapered and/or off-center
> (yes, I know you can buy special center pins, but "real hams" don't). All
> these things are failures waiting to happen.
> 
> I still have a few Ns in the 432 1.5kW setup, but those are new plugs with
> captive pins and have been fitted very carefully. If they're not OK, they
> let me know pretty quick, and then are replaced with 7/16.
> 
> Start looking out for 7/16 at hamfests. They used to be very rare in
> Britain, but  thanks to the cellular industry they quite suddenly
> started to appear as surplus over the last year or two.
> 
> 73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
>                           'In Practice' columnist for RadCom (RSGB)
>                            http://www.ifwtech.com/g3sek
> 
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> 


73, Tom W8JI
w8ji@contesting.com

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