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In message <vkckph$1cvdj$1@dont-email.me>, Jeroen Belleman <jeroen@nospam.please> writes
On 12/23/24 18:58, Ralph Mowery wrote:Yes - the 'innards' are essentially the same. IIRC, the BNC innards also mate with C-connectors. I think it's deliberate. After all, its the
In article <nnd$23e91f0d$053bf96e@d25fd620e9918bf1>, noreply@ademu.nl
says...
It is the N connector the center pin is different. The BNC pin is
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.
the
same. It is the ammount of dialectric (insulation) in the BNC that
makes it a 75 or 50 ohm connector.
N connectors are good, but the fact that 75 and 50 Ohm connectors
are similar enough to mate, but not nearly enough to do so without
damage or malfunction is perverse. When I took charge of the
electronics lab, it took a while to sort them out and to eliminate
the victims of mismatched matings. (I was always amazed at the
sheer quantity of connectors in a busy lab.)
For BNCs, there *is* a difference, but it doesn't usually matter.
I kept 50 and 75 Ohms separate, but when put to the test, many
75 Ohm connectors turned out to really be 50 Ohm ones in disguise.
In a pinch, BNC and N can even mate between them. I'm not sure if
that's deliberate or accidental.
innards that carry the RF.
On Mon, 23 Dec 2024 08:16:15 +0000, Jeff Layman <Jeff@invalid.invalid>
I did actually build one a few years ago with swappable bulbs for
different loads. Two problems, though:
1) I'd have to remember to use it
2) I'd have to somehow find it.
I think that you might have to add a third one in future - finding an
incandescent bulb to use!
Yes, getting harder as time goes by, so I stocked-up in advance and
put a couple of dozen aside while they were still widely available. I
would imagine the oven types will still be around for a few more
years, anyway - and they tend to be more robust.
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.
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.
On 23/12/2024 10:31, Cursitor Doom wrote:
On Mon, 23 Dec 2024 08:16:15 +0000, Jeff Layman <Jeff@invalid.invalid>
I did actually build one a few years ago with swappable bulbs for
different loads. Two problems, though:
1) I'd have to remember to use it
2) I'd have to somehow find it.
I think that you might have to add a third one in future - finding an
incandescent bulb to use!
Yes, getting harder as time goes by, so I stocked-up in advance and
put a couple of dozen aside while they were still widely available. I
would imagine the oven types will still be around for a few more
years, anyway - and they tend to be more robust.
I doubt they'll be able to replace the oven illumination easily (unless
they mount the bulb on the outside and use fibreoptics to bring light to
the inside!). I was surprised a few months ago when I bought a new
microwave oven to find it had an LED lamp which illuminated the inside.
I would have thought that with around a kW of microwave energy being >generated that would have been a pretty hostile environment for an LED
lamp. Obviously, though, they had the screening well sorted out. I
suppose that I shouldn't have been surprised as the timing and display >circuitry have been around for years and hasn't been affected by the RF >energy or switching spikes.
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
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
In message <nnd$23e91f0d$053bf96e@d25fd620e9918bf1>, Arie de Muijnck ><noreply@ademu.nl> writes
On 2024-12-23 16:22, Ian Jackson wrote: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',
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.
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.
In article <8i6omj1vidqoch9421207205iajrb0h5ue@4ax.com>,
cd@notformail.com says...
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
I could not get the calculator to come out for me. Getting negative
numbers and about 10 times what they should be.
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 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',
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.
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.
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 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.
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.
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.
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
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
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>Negative values for Z0? That would be surprising, because
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.
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>Negative values for Z0? That would be surprising, because
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.
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 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>Negative values for Z0? That would be surprising, because
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.
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>Negative values for Z0? That would be surprising, because
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 JacksonIt's right all right.
<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. >>>>>>
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.
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 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 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.
