In message , Jimbo
writes

"Ian Jackson" wrote in message
...
In message , S&DWS via
rec.radio.info Admin writes

Sheffield & District Wireless Society

///////////////////////////////////////////
Foundation Course Material in PDF Format

Posted: 18 Aug 2017 04:04 AM PDT
http://sheffieldwireless.org/2017/08...aterial-in-pdf
-format/


PDF File versions for the Foundation Course

Please may I offer one correction:

In 'Antennas & Feeders', the information about BNC connectors, you are
warned
"Take care not to mix incompatible 50 and 75 Ohm versions which have
different inner pin sizes".

This is NOT totally correct. While the profile of the pins are slightly
different (the 50 ohm usually has a somewhat stubbier point), the
diameters are the same. The difference in characteristic impedance is
achieved by the amount of PTFE dielectric.

As a result, you CAN physically mate 50 and 75 ohm BNC connectors (both
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 .......

For 43 years, my day job was cable TV - so I've rarely used anything
other than 75 ohm coax!

Some cable TV trunk coax used to be (as one of my bosses put it) "as
thick as a horse's prick". Unfortunately, it was not too convenient for
home use.

But as for BNC connectors, they are essentially the same as the innards
of 50 ohm N-connectors. You can mate a female BNC with a male 50 ohm N.

However, note that you can't inter-mate 50 and 75 ohm N-connectors, as
the 75 ohm has a much thinner pin.

A 50 ohm female in a 75 ohm male won't make contact (unless you put a
bit of wire inside the female receptacle). A 50 ohm male fully mated
with a 75 ohm female will splay the receptacle, and cause usually
permanent damage.



--
Ian