Re: Some comments on calibrating a Tektronix CFC250 100MHz frequency counter.
I must disagree with some of this.? In fact there was a rush ?Because patents were expiring.? The alternate line scanning used for monochrome and color was to reduce bandwidth. A big problem was the desire to make color compatible with monochrome.? The CBS field sequential system could not render motion without serious artifacts.? ? The final NTSC system was actually pretty good but it's potential had to wait for three line delay to be available.? A large part of the color gamut problems were due to phosphor limitations. There are many details. I agree with your friend that color was rushed into production before the technology was adequately developed . The reason is simply the economics of business.? Add that color did not increase the audience or advertising revenues. I also spent most of my professional life in broadcasting.
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Re: Some comments on calibrating a Tektronix CFC250 100MHz frequency counter.
There is also SECAM="System Entirely Contrary to the American Method" and PAL="Picture At Last" ?:)
Ozan
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On Thu, Mar 30, 2023 at 05:30 PM, Jim Strohm wrote:
And all these years I thought that NTSC stood for "Never The Same Colour".
?
Jim N6OTQ
NTSC was the "National Television Standards Committee' which originally set the standards for Monochrome Television, then later chose the modifications to allow color without a severe beat in the Chroma.?
?
?
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Re: Some comments on calibrating a Tektronix CFC250 100MHz frequency counter.
The 60 Hertz sync frequency was shifted to 59.94 Hertz.
The 15,750 Hertz sync frequency was shifted to 15, 734 Hertz.
8 cycles of studio 3.579540 MHz (315/88) reference frequency
was inserted on the back porch of the horizontal sync pulse
of each of the 525 lines. The 8 cycles was filtered and then
injected into a simple diode phase comparator along with a
sample of the television's own 3.579540 MHz crystal oscillator,
which generated a voltage that was applied to a reactive
tuning device such as a tube or varactor and phase locked the
television's local 3.579540 MHz oscillator to that of the studio.
Older B&W television circuits worked without issue using the
revised synch rates.
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Re: Some comments on calibrating a Tektronix CFC250 100MHz frequency counter.
and PAL may mean Probably Always Laughing after they saw NTSC.
and yeah, I heard that about NTSC.? Who said that variety isn't nice?
Harvey
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On 3/30/2023 8:30 PM, Jim Strohm wrote: And all these years I thought that NTSC stood for "Never The Same Colour".
Jim N6OTQ
On Thu, Mar 30, 2023 at 7:26?PM Michael A. Terrell <terrell.michael.a@...> wrote:
NTSC was the "National Television Standards Committee' which
originally set the standards for Monochrome Television, then later
chose the modifications to allow color without a severe beat in
the Chroma.
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Re: Some comments on calibrating a Tektronix CFC250 100MHz frequency counter.
And all these years I thought that NTSC stood for "Never The Same Colour".
Jim N6OTQ
NTSC was the "National Television Standards Committee' which originally set the standards for Monochrome Television, then later chose the modifications to allow color without a severe beat in the Chroma.?
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Re: Some comments on calibrating a Tektronix CFC250 100MHz frequency counter.
NTSC was the "National Television Standards Committee' which originally set the standards for Monochrome Television, then later chose the modifications to allow color without a severe beat in the Chroma. From memory, vertical was 59.94 Hz and horizontal was 15, 734.34 Hz. Stations typically ran 60/15,750 if they only transmitted in monochrome. I was the engineer at a station like that in 1973'74.which made it difficult but not impossible to transmit our station ID in color without? any color equipment. Our master sync generator had a Genlock input that I drove from a color bar generator. It was first generation Grass Valley, and used RTL or DTL logic. There were circuits that used frequency multiplication and dividers to convert Colorburst to 5 000 MHz, but it was only accurate if it was a network feed that wasn't modified at a local TV station, which was rare. The stations I worked at used a cheap 14.318.189 MHz crystal instead of a rubidium master oscillator.
As I recall, the "60 Hz" vertical scan rate for NTSC is not supposed to be exactly 60 Hz, but slightly different, to provide color and still maintain integer counting values. Likewise, the horizontal is not 15,750 Hz as in monochrome, but something like 15,734. This was all part of the trick to squeeze the vector modulated color info into the spaces between the normal monochrome scan spectral lines, and magically work for both color and B&W TV sets, with "mostly" full compatibility, and without needing any extra channel bandwidth. If you study up on NTSC, you can get the exact values and rationale of the scheme. I've always found it quite fascinating how this was figured out and done way back when. I used to understand it, but it's been a lot of years.
Anyway, you can force your unit to run at exactly 60 Hz by tweaking the oscillator to match whatever divide ratio is used. The HP/Grass Valley thing likely wasn't intended to make exactly 60 Hz, but the NTSC version of it. Changing that to real 60 Hz would be a much bigger project.
Ed
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Re: Some comments on calibrating a Tektronix CFC250 100MHz frequency counter.
59.94 IIRC.? The color subcarrier frequency was chosen to put the energy of the color subcarrier in between the energy created by the monochrome image.? I think they changed the audio subcarrier frequency a bit, just to avoid the beat frequency between the audio and the color information.
Everything was derived from 14.31818 Mhz, which generated the horizontal and vertical frequencies, and kept the picture artifacts minimized.
The I and Q modulation was picked so that the major amount of energy was low (since they decided that people couldn't see certain colors, so that large objects are all three colors, and the next set of color details are only two colors.? Anything higher than 1.5 Mhz in the old NTSC is black and white, IIRC.
Harvey
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On 3/30/2023 7:41 PM, Ed Breya via groups.io wrote: As I recall, the "60 Hz" vertical scan rate for NTSC is not supposed to be exactly 60 Hz, but slightly different, to provide color and still maintain integer counting values. Likewise, the horizontal is not 15,750 Hz as in monochrome, but something like 15,734. This was all part of the trick to squeeze the vector modulated color info into the spaces between the normal monochrome scan spectral lines, and magically work for both color and B&W TV sets, with "mostly" full compatibility, and without needing any extra channel bandwidth. If you study up on NTSC, you can get the exact values and rationale of the scheme. I've always found it quite fascinating how this was figured out and done way back when. I used to understand it, but it's been a lot of years.
Anyway, you can force your unit to run at exactly 60 Hz by tweaking the oscillator to match whatever divide ratio is used. The HP/Grass Valley thing likely wasn't intended to make exactly 60 Hz, but the NTSC version of it. Changing that to real 60 Hz would be a much bigger project.
Ed
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Re: Some comments on calibrating a Tektronix CFC250 100MHz frequency counter.
As I recall, the "60 Hz" vertical scan rate for NTSC is not supposed to be exactly 60 Hz, but slightly different, to provide color and still maintain integer counting values. Likewise, the horizontal is not 15,750 Hz as in monochrome, but something like 15,734. This was all part of the trick to squeeze the vector modulated color info into the spaces between the normal monochrome scan spectral lines, and magically work for both color and B&W TV sets, with "mostly" full compatibility, and without needing any extra channel bandwidth. If you study up on NTSC, you can get the exact values and rationale of the scheme. I've always found it quite fascinating how this was figured out and done way back when. I used to understand it, but it's been a lot of years.
Anyway, you can force your unit to run at exactly 60 Hz by tweaking the oscillator to match whatever divide ratio is used. The HP/Grass Valley thing likely wasn't intended to make exactly 60 Hz, but the NTSC version of it. Changing that to real 60 Hz would be a much bigger project.
Ed
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Re: slightly off topic feel free to delete
Hi Michael,
?What you say about your experience may be be true, on the other hand I have had a 250ft length of
CAT5 feeding my Icom R-71a for about 10 years, in Florida, and so far all is good.
Plenty of people with coax antenna leads have had their radios damaged by lightning,
?Lightning is like water, "water always wins, just look at the Grand Canyon". :-)
?????????????????????????????????????????? Mikek
?PS. miss you over on SED.
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Re: slightly off topic feel free to delete
The statement that capacitance decreases as the turns per unit
increases is wrong, the capacitance will INCREASE.?
Don't believe everything that an AI claims.
Leon Robinson ?? K5JLR
Political Correctness is a Political Disease.
Politicians and Diapers should be changed
often and for the same reasons.
On Wednesday, March 29, 2023 at 06:18:18 PM CDT, John Kolb <jlkolb@...> wrote:
The impedance can vary
with the number of turns per distance.
"The
characteristic impedance of a transmission line is determined by
its physical parameters, such as the diameter of the conductors,
the spacing between them, and the dielectric material between
them. Twisting the conductors of a transmission line changes these
physical parameters and can alter the characteristic impedance.
When the number of turns per unit distance is increased, the
capacitance between the conductors decreases, and the inductance
increases. This change in capacitance and inductance can cause the
characteristic impedance to change."??? chatGPT
When I worked at Southcom International, the engineer had a chart
for 28 and 30 ga wire with Z vs turns per inch.
John ?? KK6IL
On 3/29/2023 8:51 AM, Mikek wrote:
>
unshielded twisted pair ethernet cables:
> I think the nominal impedance is 150 ohms
?I think twisted pairs are closer to 100Ω, I once measured one
and got 102Ω.
It is dependent in the diameter of the wire and the thickness of
the insulation.
Using the calculator,?
I get a slight lower number for a Cat5 wire I have, it is 24
gauge with polyethylene?
insulation that is 0.075" thick. This puts the 0.0201" wire
spaced 0.015" by the
insulation that has an er of 2.25 at a center to
center distance of 0.035" and an impedance of 92Ω.
?If the spacing of the center to center distance is increased
0.003" the impedance becomes 100Ω.
Or if the er is lowered to 1.9 the impedance is 100Ω.
i.e. I could have a little error in the thickness
and/or the er of the insulation, a small change could
get me close to 100Ω.
????????????????????????????? Mikek
.
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Re: slightly off topic feel free to delete
The impedance can vary
with the number of turns per distance.
"The
characteristic impedance of a transmission line is determined by
its physical parameters, such as the diameter of the conductors,
the spacing between them, and the dielectric material between
them. Twisting the conductors of a transmission line changes these
physical parameters and can alter the characteristic impedance.
When the number of turns per unit distance is increased, the
capacitance between the conductors decreases, and the inductance
increases. This change in capacitance and inductance can cause the
characteristic impedance to change."??? chatGPT
When I worked at Southcom International, the engineer had a chart
for 28 and 30 ga wire with Z vs turns per inch.
John ?? KK6IL
On 3/29/2023 8:51 AM, Mikek wrote:
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Show quoted text
>
unshielded twisted pair ethernet cables:
> I think the nominal impedance is 150 ohms
?I think twisted pairs are closer to 100Ω, I once measured one
and got 102Ω.
It is dependent in the diameter of the wire and the thickness of
the insulation.
Using the calculator,?
I get a slight lower number for a Cat5 wire I have, it is 24
gauge with polyethylene?
insulation that is 0.075" thick. This puts the 0.0201" wire
spaced 0.015" by the
insulation that has an er of 2.25 at a center to
center distance of 0.035" and an impedance of 92Ω.
?If the spacing of the center to center distance is increased
0.003" the impedance becomes 100Ω.
Or if the er is lowered to 1.9 the impedance is 100Ω.
i.e. I could have a little error in the thickness
and/or the er of the insulation, a small change could
get me close to 100Ω.
????????????????????????????? Mikek
.
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Re: slightly off topic feel free to delete
To add to this… ? The number of twists per foot determines the differential-mode susceptibility of the cable. More twists per foot, higher rejection of differential energy. ? It does not improve the Common Mode environment susceptibility though – the cable is still a monopole receive or transmit antenna. ? Shielding and properly terminating the shields helps with Common-mode susceptibility and emissions. ? Ross ?
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From: [email protected] < [email protected]> On Behalf Of Tom Lee Sent: Wednesday, March 29, 2023 10:16 AM To: [email protected]Subject: Re: [Test Equipment Design & Construction] slightly off topic feel free to delete ? And I should have added that the impedance is measured at a frequency of 100MHz.
-- Prof. Thomas H. Lee Allen Ctr., Rm. 205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 On 3/29/2023 09:14, Tom Lee wrote: If you take random hookup wire and twist it with some random pitch, you'll often see something closer to 100 than to 150, but 150 is certainly not out of the question. That said, CAT5 is spec'd at 100 ohms, plus or minus 5 ohms.
-- Cheers
Tom
-- Prof. Thomas H. Lee Allen Ctr., Rm. 205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 On 3/29/2023 08:51, Mikek wrote: > unshielded twisted pair ethernet cables:
> I think the nominal impedance is 150 ohms
?I think twisted pairs are closer to 100Ω, I once measured one and got 102Ω.
It is dependent in the diameter of the wire and the thickness of the insulation.
Using the calculator,?
I get a slight lower number for a Cat5 wire I have, it is 24 gauge with polyethylene?
insulation that is 0.075" thick. This puts the 0.0201" wire spaced 0.015" by the
insulation that has an er of 2.25 at a center to center distance of 0.035" and an impedance of 92Ω.
?If the spacing of the center to center distance is increased 0.003" the impedance becomes 100Ω.
Or if the er is lowered to 1.9 the impedance is 100Ω. i.e. I could have a little error in the thickness
and/or the er of the insulation, a small change could get me close to 100Ω.
????????????????????????????? Mikek
.
?
?
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Re: Signal Ingress-- coax vs CAT5
Fifty years ago I fabricated and sold 1-M diameter, single-turn, resonant-loop antennas for the AM broadcast band.? These were designed to recover a virtually noise-free signal for AM broadcasters with studios in downtown office buildings where elevator noise and other interference was a significant problem.? Coaxial cable lead-ins just did not work.? The solution was simply shielded audio wire with a ferrite balanced-to-unbalanced transformers at the modulation monitor or other equipment end, as the very low impedance feed from the center-grounded loop antenna was well-balanced.? As I recall, such shielded audio cables measured in the 100 to 150-ohm range.
Bruce, KG6OJI
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Signal Ingress-- coax vs CAT5
I have seen a little discussion of feed line ingress amplitude with coax vs twisted pair.
My position was influenced by Dallas Lankford when he was building directional phased MW antenna systems.
When he was having a hard time nulling an unwanted signal and tried a twisted pair speaker wire, it was a but of a
eureka moment for him and he continued using twisted pair and also CAT5 cable.
?? I would like to see definitive tests done on the question, Such as stretch out 150ft of coax and 150ft of CAT5 on the ground
and do listening tests.
Questions I have,
I suspect you would want to terminate the far end in the cables in their characteristic impedance.
For the CAT5, a 100Ω to 50Ω transformer should be used at the input of the testing receiver.
?What should be done to the other 3 pairs in the CAT5?
How about parallel connecting two of the twisted pair in a CAT5 for a 50Ω characteristic impedance?
How does that affect the signal ingress?
MW is good for testing, because of large continuous signals to measure signal strength.
I don't know how well that translates to HF.
?I know Common modes chokes can be added to both to reduce ingress.
There are different qualities of both Coax a (solid braid) and CAT5/6 (UUTP, F/UTP, and F/FTP)
So, I would expect a comparison of better quality cables.
?I'd like your thoughts on how this test would be performed, I suspect a Spectrum analyzer would be useful in the testing.
??????????????????????????? Thanks, Mikek
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Re: slightly off topic feel free to delete
USTP works, but not a good idea in areas with a lot of lightning strikes. Back in the '80s I maintained a 36 channel Cable TV headend. One strike blew out 12 audio inputs on the modulators, and caused distortion in a few more. I replaced the cables with single pair shielded audio cable and never lost another CA3240 FET input op amp afterwards.
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Re: slightly off topic feel free to delete
And I should have added that the impedance is measured at a
frequency of 100MHz.
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
On 3/29/2023 09:14, Tom Lee wrote:
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Show quoted text
If you take random hookup wire and twist it with some random
pitch, you'll often see something closer to 100 than to 150, but
150 is certainly not out of the question. That said, CAT5 is
spec'd at 100 ohms, plus or minus 5 ohms.
-- Cheers
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
On 3/29/2023 08:51, Mikek wrote:
>
unshielded twisted pair ethernet cables:
> I think the nominal impedance is 150 ohms
?I think twisted pairs are closer to 100Ω, I once measured one
and got 102Ω.
It is dependent in the diameter of the wire and the thickness
of the insulation.
Using the calculator,?
I get a slight lower number for a Cat5 wire I have, it is 24
gauge with polyethylene?
insulation that is 0.075" thick. This puts the 0.0201" wire
spaced 0.015" by the
insulation that has an er of 2.25 at a center to
center distance of 0.035" and an impedance of 92Ω.
?If the spacing of the center to center distance is increased
0.003" the impedance becomes 100Ω.
Or if the er is lowered to 1.9 the impedance is
100Ω. i.e. I could have a little error in the thickness
and/or the er of the insulation, a small change
could get me close to 100Ω.
????????????????????????????? Mikek
.
|
Re: slightly off topic feel free to delete
If you take random hookup wire and twist it with some random pitch,
you'll often see something closer to 100 than to 150, but 150 is
certainly not out of the question. That said, CAT5 is spec'd at 100
ohms, plus or minus 5 ohms.
-- Cheers
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
On 3/29/2023 08:51, Mikek wrote:
toggle quoted message
Show quoted text
>
unshielded twisted pair ethernet cables:
> I think the nominal impedance is 150 ohms
?I think twisted pairs are closer to 100Ω, I once measured one
and got 102Ω.
It is dependent in the diameter of the wire and the thickness of
the insulation.
Using the calculator,?
I get a slight lower number for a Cat5 wire I have, it is 24
gauge with polyethylene?
insulation that is 0.075" thick. This puts the 0.0201" wire
spaced 0.015" by the
insulation that has an er of 2.25 at a center to
center distance of 0.035" and an impedance of 92Ω.
?If the spacing of the center to center distance is increased
0.003" the impedance becomes 100Ω.
Or if the er is lowered to 1.9 the impedance is 100Ω.
i.e. I could have a little error in the thickness
and/or the er of the insulation, a small change could
get me close to 100Ω.
????????????????????????????? Mikek
.
|
Re: slightly off topic feel free to delete
> unshielded twisted pair ethernet cables:
> I think the nominal impedance is 150 ohms
?I think twisted pairs are closer to 100Ω, I once measured one and got 102Ω.
It is dependent in the diameter of the wire and the thickness of the insulation.
Using the calculator,?
I get a slight lower number for a Cat5 wire I have, it is 24 gauge with polyethylene?
insulation that is 0.075" thick. This puts the 0.0201" wire spaced 0.015" by the
insulation that has an er of 2.25 at a center to center distance of 0.035" and an impedance of 92Ω.
?If the spacing of the center to center distance is increased 0.003" the impedance becomes 100Ω.
Or if the er is lowered to 1.9 the impedance is 100Ω. i.e. I could have a little error in the thickness
and/or the er of the insulation, a small change could get me close to 100Ω.
????????????????????????????? Mikek
.
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Re: slightly off topic feel free to delete
Hi:
If the length of coax is less than about 1/10 of a wavelength then
you can approximate it with lumped elements, so the Zo is not that
important.
The impedance of coax is NOT a constant, so when used for audio you
need to look at more parameters than just the nominal impedance.
See:?
--
Have Fun,
Brooke Clarke
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
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Some more thoughts on impedance.
?
I had a discussion with some EE
professors about coax cable, impedance, loss, loss due to the
"wrong impedance" and one suggested this article:
?
I doubted the claimed loss due to
mismatch, until I worked out the Telegraphers Equation for
myself.
?
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slightly off topic feel free to delete
Interesting topic! Cable impedance vs. loss. I remember reading, many years ago, about power handling vs. vs calculation concerning impedance for coax. The article said 30 ohms was the best power handling in a coax while 72.5 ohms was the lowest loss!?
During WWII there were committees on coax standards and fittings. It was decided that the best overall value for power and loss was 52.5 ohms (halfway between ?) which became our 50 ohm standard. And 75 ohms was best for low loss. Then there was 93 ohms for pulse cable (radar baseband pulse).
And BTW, Oliver Heaviside of the Telegraphers Equation (basic Zo of transmission lines) is the inventor of coax cable (around 1890 or so).
Respectfully?
J.Kruth
?
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Michael A. Terrell
John Kolb
ebrucehunter