In message , Brian Reay writes
On 19/08/17 13:05, Ian Jackson wrote:
In message , Gareth's Downstairs Computer
writes
On 19/08/2017 10:34, Jimbo wrote:
sexes).
when I was newly licensed and poor I used 75 ohm TV coax and
belling lee
connectors on HF and got away with it .......


And it was standard on 145MHz. (QQV03-10 anyone?)
Actually, the original B&L connector is a pretty good 75 ohm match
up to 1GHz and more. If I remember correctly, many 50 ohm BNCs are
not so hot
500MHz. With 75 ohms, the problem is maintaining the structural
return
loss constant while having enough PTFE insulation to hold the pin in
place. Some are only really good to around 200Mhz. Of course, for most
purposes, both are usable to much higher frequencies.
And mixable!

Well, the B&L connectors are used for TV which covers well into the
100s of MHz. There is also the F connector, another 'cheap and
cheerful' beast, used beyond 1GHz. I've not done any measurements but
it obviously performs were enough for the task demanded of it.

Both the B&L and F connector suffer (as do all connectors) problems if
not fitted correctly but they are more prone to being 'bodged'.

As already mentioned about the N-connector, the B&L assembly is almost
specifically designed to be botched. [Note: 'Botched' is the word, not
'bodged'!]

The B&L is, for example. prone to issues with poor braid bonding while
the F connector, which uses the centre conductor as the pin, tend to be
prone to the 'pin' not aligning etc. I believe the F connector is used
in the US where we would, generally, expect to see a B&L connector. I
believe the B&L is virtually unknown in the US. I was contacted by a US
amateur some time back who had acquired a bit of UK kit (KW?) which had
B&L sockets. He'd not seen them before. I sent him some plugs etc.

These days, because of the American use, the F-connector is the standard
RF connector on all customer cable TV equipment (and also used a lot on
headend and associated equipment).

One technical virtue of the F male connector is that the 'pin' is simply
the cable inner. That should not prevent it aligning with the female
receptacle, unless whoever cut the cable bent it while doing so. It
helps mating if the inner is cut to the correct length, ie protruding
1/16th inch.

While the structural return loss of the F male connector is essentially
perfect, it's the capacitance of the female that limits the top
frequency. Like many connectors, it can be used at frequencies well
above where it should be!

These days, the cable TV industry uses various types of 'snap and seal'
male connectors (the old crimp type are definitely verboten). However,
for home use, for convenience I normally use the domestic screw-on type.
Like the B&L, the secret is knowing what to do with the braid.

Of course, there is nothing 'magic' about 50 ohm coax or the connectors
we 'normally' use on our radios. If we were to stick to using 75 ohm
coax and B&L connectors the world wouldn't end. Likewise, if you mixed
50 ohm and 75 ohm, while you may be able to measure a slight
difference, chances are, in real terms, it wouldn't make much
difference to the overall set up performance- at least unless you were
doing something 'exotic'. You'd be more likely to notice the impact of
a poorly fitted 'correct' connector in an all 50 ohm system.

The company once had a clear-out, and (among a lot of stuff) was going
to dump several 1000' reels of RG11. Needless to say, I and another
licensed co-worker tried to help them out with some of the cable. We
offered it to three or four of the local clubs, but it was refused on
the grounds that it was 75 ohms.

I tend to favour N types but I've not change all the connectors on my
radios. The 'first' patch lead as whatever the radio needs on one end
and required N type to connect to rest on the station on the other. The
same for my mobile set ups.

I also have a good collect of, quality, interseries, adaptors etc and a
set of the correct connectors for my Bird power meters and dummy load
etc. Through in a few home brew special adaptor leads for things I
don't have adaptors for and I can interconnect virtually anything.






--
Ian