Tom Rauch wrote:
>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.
>
All true... of the traditional N connector design which still seems to
be very common in the USA.
The improved "pressure sleeve" design meets all Tom's objections -
except of course for the size of the center pin.
In the "improved" design the center pin is captive and cannot move
lengthways (except under a lot of sustained force). The contact to the
braid is via a ferrule that slips under the braid, and the rubber
pressure sleeve slips over the jacket. When the back nut is tightened,
the sleeve compresses the braid into contact just like Tom says it
should. For people who haven't seen this style of connector, the
pressure sleeve is not like the wimpy rubber washer in the traditional
design - it grips the cable so firmly you can swing on it, and the water
seal is excellent.
Same applies to BNC. The pressure sleeve plugs are so much more
reliable, I won't use the traditional type at all.
It seems surprising that the old-style N and BNC plugs are still made at
all. In Europe they have mostly been the pressure sleeve design for 20
years or more.
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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