<<Most hams know that the standard BNC (not the mini
version)
should handle 200-300 watts and not be pushed higher, altho
likely will go
higher for some time.>>
The BNC, either 50 or 75 ohm, is dimensionally almost
identical to the 50-ohm style type N connector. As a matter
of fact we use BNC males with the locking ring removed as
push on connectors to mate with 50 ohm N females. All we
have to do is very slightly flare the BNC mating ground
shell to increase pressure a bit on the inside of the N.
The weak point is the cable with BNC's, not the connectors.
The connectors, like a type N, will handle a few kilowatts
into a matched load.
<<The So-239 is often rated at a Kilowatt of RF but clearly
takes double
that in many many shacks. However, at about 6 KW with a
small
SWR, the SO-239 will begin to arc the pin to shield.>>
We high-pot SO-239/PL-259 combos at 5,000 volts peak. A good
connector properly installed will easily make that number.
5000*.707 is 3500 VRMS. That's 250kW into 50 ohms, so arcing
is never the issue in a properly installed connector. They
are current limited which is a heating problem, but will
easily handle five times the current of a type N because the
pin surface area is much larger.
Whenever we install connectors we high pot them to be sure
we have no stray strands or other problems. We flatly reject
anything below 3.5 kV, but prefer to have 5kV or more.
<The big one that looks something like a BNC, called an N,
has many advantages including taking higher RF, presenting
a lower SWR bump in the line, greater shielding of the
shield line,>>
I disagree Charlie. There is a HN we use in plasma and other
high power high SWR applications, but a type N like the BNC
is really a weak connector. The N is a glorified weather
tight BNC. I'd never consider a type N at more than 1500
watts or especially into a high SWR. They are terrible for
lightning and SWR related damage because they have very
small center pins and very close internal spacing. The HN is
much better if you want a reliable connector that is N
style. That's all we use on high power plasma and medical.
The impedance bump in a UHF is limited to an area about 1/2
inch long. The problem is all in the female, the male (like
most males) is nearly perfect. You wind up with 1/2 inch of
30-45 ohm line section for every standard properly installed
UHF connector pair. The general electrical rule is a
moderately sensitive system like a communications system can
have about 1 degree of bump at that SWR, so the UHF
connector should be good up to lower UHF with problems
unless you get too many in the system. This is why Motorola
never had a problem with UHF connectors on VHF gear.
As a matter of fact when I install hardline here I actually
machine the N female ends and convert them to UHF females
with Teflon insulation. We've had N's blow right apart in
lighting hits, but the UHF connectors keep on ticking. For
UHF weak signal I might consider an N, but they are
unreliable at high power or with high SWR or lightning.
At low power where a cable needs to be quickly disconnected
a BNC is fine, but I'd never use them here for anything
outside of the test bench or a radio that needs a quick
disconnect. Ham manufacturers did the right thing by using a
UHF connector. It was generally a smart move.
73 Tom
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