The mating parts of the pins of N and BNC are similar sizes. The rest of
the pins are not. N is mostly air insulated so the outsides of the pin
and socket beyond the mating portion is a different size to maintain 50
ohms impedance. 75 ohm pins are smaller in diameter to maintain
impedance match.
UHF connectors where NAMED UHF in a day when UHF was 20 MHZ. They have
multiple limitations. First their impedance is not 50 or 75 ohms. Second
their ground connection between connectors depends entirely on the
tightness of the ring. Finger tight with vibration is not tight. I've
burned a pair of connectors black with only 18 watts in a mobile
installation. Then there's their attachment. Screwing and soldering the
standard 83-1SP to RG-8 coax is far more difficult (though when done
right its quite secure) than installing any version of N or BNC. There
are many such connectors in ham shacks improperly installed. Those
alternative installation details tend to lead to open braid connections
and thus to TVI from coax radiation, and poor receive from coax line
noise pickup and mismatch. UHF cause mismatch, the center pin may
tolerate it but the foibles of the outer connection and the plain
mismatch of the connector lead to problems in the long run.
73, Jerry, K0CQ
--
Entire content copyright Dr. Gerald N. Johnson. Reproduction by
permission only.
|