Re: Francophones

On Wed, 25 Dec 2024 22:18:21 +0000, Ian Jackson
<ianREMOVETHISjackson@g3ohx.co.uk> wrote:

In message <l7vomj55u59o3cu753v7de77t0j4n20jtp@4ax.com>, john larkin
<JL@gct.com> writes

On Mon, 23 Dec 2024 23:05:03 +0000, Ian Jackson
<ianREMOVETHISjackson@g3ohx.co.uk> wrote:
>

In message <nnd$23e91f0d$053bf96e@d25fd620e9918bf1>, Arie de Muijnck
<noreply@ademu.nl> writes

On 2024-12-23 16:22, Ian Jackson wrote:

For many purposes you can ignore the difference between the 50 and 75
ohm impedances (and 60 if you ever come across any). However, be very
aware only BNC 50 and 75 ohm connectors are mutually mechanically
mateable (yes - they really are!). I don't know if any others that are.

>
Not recommended.
The center pin differs, a 50 Ohm BNC pin is thicker and may damage a 75
ohm BNC.
I'm cautious, most of my below 1 GHz equipment is 75 Ohms (from CATV
company), the rest is 50.
>

For most of its length, the male BNC 50 ohm pin is actually the same
diameter as the 75. However, the tip of the 50 pin is fairly 'blunt',
while the 75 is more pointed.
>
I guess that if you are particularly clumsy while you are inserting a 50
male into a female 75, it might just be possible to have the blunter
male pin a bit off-centre, and catch the side of the female receptacle,
and splay it. However, despite 43 years working in the CATV industry, I
failed to achieve this!
>
The real difference between the two impedances is that the amount of
PTFE dielectric in the 75 has been minimised in order to increase (with
some difficulty) the Zo from 50 to 75 ohms. IIRC, the 50 has a
more-uniform structural RLR, so it the better connector at the higher
frequencies.

>
The critical part of the connector here is a fraction of an inch long,
so none of this stuff matters below a few GHz.

>
Yes. Obviously.
I've been retired now for many a year but, IIRC, the 50 ohm was
considered 'good' to around 1000 MHz, and the 75 to around 500MHz. [A
Google on the individual manufacturers' specs is recommended.]
Regardless, both are often used to higher frequencies.

>

Here's a BNC tdr/tdt. It's really not so bad.

https://www.dropbox.com/scl/fi/1yklmtb4gxanwn7c5ldlx/BNC_TDR_TDT.JPG?rlkey=f8ro6nzy7n2nvdfjqfu1b36rf&raw=1

https://www.dropbox.com/scl/fi/oacgzpebcjbhxg396hytq/BNC_TDR_ZOOM.JPG?rlkey=8j0ke6s8rw424t6q0ik6ohzp0&raw=1

https://www.dropbox.com/scl/fi/gldt1avq6edxqzvgnitvx/BNC_TDT_RISE.JPG?rlkey=lc3w3zb8naegvf1x5pmq8r11g&raw=1