On Wed, 25 Dec 2024 14:48:20 +0000, Cursitor Doom <cd@notformail.com>
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

That calc is nonsense. Reasonable entries generate negative values and
a preposterous cutoff frequency.

On 12/26/24 00:15, john larkin wrote:
> On Wed, 25 Dec 2024 14:48:20 +0000, Cursitor Doom <cd@notformail.com>
> 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
>
> That calc is nonsense. Reasonable entries generate negative values and
> a preposterous cutoff frequency.
>
Negative values for Z0? That would be surprising, because
the equation is correct, even though the physics are
obfuscated away into a few magic factors.

Example please?

Jeroen Belleman

On Fri, 27 Dec 2024 16:23:58 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:

>On 12/26/24 00:15, john larkin wrote:
>> On Wed, 25 Dec 2024 14:48:20 +0000, Cursitor Doom <cd@notformail.com>
>> 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
>>
>> That calc is nonsense. Reasonable entries generate negative values and
>> a preposterous cutoff frequency.
>>
>Negative values for Z0? That would be surprising, because
>the equation is correct, even though the physics are
>obfuscated away into a few magic factors.
>
>Example please?
>
>Jeroen Belleman

https://www.dropbox.com/scl/fi/aglpygrtir3m9bccil1to/EvRfZcalc.jpg?rlkey=nazlwgbmpvbssz5zv2a92hrqj&raw=1

On Fri, 27 Dec 2024 08:21:55 -0800, john larkin <JL@gct.com> wrote:

>On Fri, 27 Dec 2024 16:23:58 +0100, Jeroen Belleman
><jeroen@nospam.please> wrote:
>
>>On 12/26/24 00:15, john larkin wrote:
>>> On Wed, 25 Dec 2024 14:48:20 +0000, Cursitor Doom <cd@notformail.com>
>>> 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
>>>
>>> That calc is nonsense. Reasonable entries generate negative values and
>>> a preposterous cutoff frequency.
>>>
>>Negative values for Z0? That would be surprising, because
>>the equation is correct, even though the physics are
>>obfuscated away into a few magic factors.
>>
>>Example please?
>>
>>Jeroen Belleman
>
>https://www.dropbox.com/scl/fi/aglpygrtir3m9bccil1to/EvRfZcalc.jpg?rlkey=nazlwgbmpvbssz5zv2a92hrqj&raw=1

GIGO. Where on earth did you get those input parameter values from?
Try it again with something more realistic.

On 12/27/24 17:21, john larkin wrote:
> On Fri, 27 Dec 2024 16:23:58 +0100, Jeroen Belleman
> <jeroen@nospam.please> wrote:
>
>> On 12/26/24 00:15, john larkin wrote:
>>> On Wed, 25 Dec 2024 14:48:20 +0000, Cursitor Doom <cd@notformail.com>
>>> 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
>>>
>>> That calc is nonsense. Reasonable entries generate negative values and
>>> a preposterous cutoff frequency.
>>>
>> Negative values for Z0? That would be surprising, because
>> the equation is correct, even though the physics are
>> obfuscated away into a few magic factors.
>>
>> Example please?
>>
>> Jeroen Belleman
>
> https://www.dropbox.com/scl/fi/aglpygrtir3m9bccil1to/EvRfZcalc.jpg?rlkey=nazlwgbmpvbssz5zv2a92hrqj&raw=1
>

Indeed! They seem to have botched the inch and cm units.
It makes better sense for the other units. It's a weird
and wonderful error to make, because it doesn't actually
matter in which units the diameters are given, as long as
they are the same! The argument of the log is dimensionless!

Shame! Obfuscate the physics and then get it wrong too!

Jeroen Belleman

On Fri, 27 Dec 2024 18:10:10 +0000, Dan Green <dhg99908@hotmail.se>
wrote:

>On Fri, 27 Dec 2024 08:21:55 -0800, john larkin <JL@gct.com> wrote:
>
>>On Fri, 27 Dec 2024 16:23:58 +0100, Jeroen Belleman
>><jeroen@nospam.please> wrote:
>>
>>>On 12/26/24 00:15, john larkin wrote:
>>>> On Wed, 25 Dec 2024 14:48:20 +0000, Cursitor Doom <cd@notformail.com>
>>>> 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
>>>>
>>>> That calc is nonsense. Reasonable entries generate negative values and
>>>> a preposterous cutoff frequency.
>>>>
>>>Negative values for Z0? That would be surprising, because
>>>the equation is correct, even though the physics are
>>>obfuscated away into a few magic factors.
>>>
>>>Example please?
>>>
>>>Jeroen Belleman
>>
>>https://www.dropbox.com/scl/fi/aglpygrtir3m9bccil1to/EvRfZcalc.jpg?rlkey=nazlwgbmpvbssz5zv2a92hrqj&raw=1
>
>GIGO. Where on earth did you get those input parameter values from?
>Try it again with something more realistic.

They are physically reasonable, not garbage. I might build a high
voltage coax from a rod in a 1" copper pipe.

No simple equation will predict PCB trace or coax impedance in the
general case. Sensible software will warn when the input values are
out of the useful range of its equations. This one just displays
nonsense.

I guess that a polynomial on D/d might be better. At least it wouldn't
go negative.

We use a real e/m simulator to verify capacitances and impedances when
we suspect that the dumb programs are being dumb. Or build one and
measure it.

On 2024-12-25, john larkin <JL@gct.com> wrote:
> On Wed, 25 Dec 2024 14:48:20 +0000, Cursitor Doom <cd@notformail.com>
> 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
>
> That calc is nonsense. Reasonable entries generate negative values and
> a preposterous cutoff frequency.

this seems to be something related to their units conversion. If you use
millimeters it gives sensible-looking answers.

--
Jasen.
🇺🇦 Слава Україні

On Sun, 29 Dec 2024 02:44:16 -0000 (UTC), Jasen Betts
<usenet@revmaps.no-ip.org> wrote:

>On 2024-12-25, john larkin <JL@gct.com> wrote:
>> On Wed, 25 Dec 2024 14:48:20 +0000, Cursitor Doom <cd@notformail.com>
>> 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
>>
>> That calc is nonsense. Reasonable entries generate negative values and
>> a preposterous cutoff frequency.
>
>this seems to be something related to their units conversion. If you use
>millimeters it gives sensible-looking answers.

That's great, a program that only usually delivers nonsense.