Re: Francophones

On 12/25/24 15:48, Cursitor Doom wrote:

On Tue, 24 Dec 2024 22:42:17 +0000, Ian Jackson
<ianREMOVETHISjackson@g3ohx.co.uk> wrote:
 

In message <6ftjmjppf4421dl2ec0ek4mvfht74lmnu2@4ax.com>, Cursitor Doom
<cd@notformail.com> writes

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

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.

>
I don't think that's quite right. The diameter of the inner and outer
conductors has more influence on Zo than the dilectric thickness.

>
It's right all right.
>
The outer diameter is the same for the 50 and 75 ohms. For the 75, I
presume it's not practicable to make the pin diameter smaller and retain
its robustness, so the only way to increase the Zo is to remove as much
of the dielectric as possible. If you compare the 50 and the 75, you
will see what I mean.

 I still maintain the principal determinants of the impedance are  as I
stated previously. The formulas for line impedance are shown on this
page and the aforementioned determinants are key.
 https://www.everythingrf.com/rf-calculators/coaxial-cable-calculator
 

Very poor web page indeed. No educational value whatever.
They lump together the values of the dieelectric constant
and the permeability of free space, the geometry of the
configuration and the conversion from natural to base-ten
logarithms all together into one magic factor, without any
hint of where it all came from.
Shame! That's not 'everythingRF': It's almost nothing!
Oh, and there is no such thing as "impedance per unit length".
Jeroen Belleman