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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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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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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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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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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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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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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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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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It was surprising the mechanical spinning disk system ever made it to market. The imagery was not bad but having the outer disk speed was fairly fast. And the drive motors were not exactly quiet. A lot of female customers complained about the noise from the disk and the mechanical vibration that frequently occurred in the flyback transformer at 17,734 Hertz. Yeah women could hear it.
Another wart in early three gun color crt technology was adjustment of the screen purity for round crts. Early color crts used steel bells which flared to matched the crt face plate. Unlike later crts which used layers of aquadag to form the high voltage filter capacitor, the metal bell crts used doorknob capacitors and the whole crt bell was run at about 22 KV. The purity was adjusted by rotating magnets positioned around the edge of glass faceplate adjacent to the crt bell. The last one I worked on had 12 magnets and you best be extra careful or the shop owner would get a phone call about the foul mouth service tech sent to her home. getting a jolt of 22 KV while adjusting purity was a right of passage in the 50's.? And those doorknob capacitors stored a grunch of current. The later glass bell crts which used the conductive aquadag to form the HV Filter capacitor did not hurt as much when you accidentally came in contact. It still hurt, but not like a high Q doorknob dumping every last electron unimpeded into a finger tip. Aye Chihauhua!
Then there were the pets. In particular cats, and especially Siamese cats. I had removed one (a Siamese cat) from the inside of a customer's console color television several times while serving the set with the back off. Motorla used nickel plated steel pins inserted into the printed circuit board in that particualr model, then wrapped the interconnecting wires around the pins using wire wrap techniques. And they stuck straight up, just waiting for a careless finger. Nothing like impaling your finger tip on one and feeling the crude finish drag against the inside of your finger as you pulled back. Back to the cat.
I asked the owner to help keep him away from the set while I had the back off, as I feared he would be injured. I could just imagine the damage that bugger could do if he stepped on the bed of those wire wrap terminals in the chassis. She removed the cat and I proceeded to change out a tube here and there. I had just inserted one tube, plugged in the ac power (cheater) cord to power the set up and turned to reach into the tube caddy for a long skinny screwdriver, when there was a squall from a creature in pain. The cat had returned, crawled in with my back turned and apparently found a B Boost (about 800 volt DC) terminal. I saw a blur as the cat left at light speed, and just sat speechless over the carnage the cat had inflicted on that poor television. IF Cans, coil forms, laid over broken, tube pins were bent so badly I feared straightening them. Several wires were torn loose. The cat survived, but he did not intrude again during that visit. And I explained to an insurance agent how the customer's cat destroyed a color television.
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The BTSC was in place in 1941 RCA developed their color system in 1953. I've met other TV engineers who had no clue about this. In the mid '70s I worked at the original Cincinnati Electronics, in a former Crosley factory. It still had the Crosley museum, and many old books including one on the release of the initial NTSC ruling. It described the details of each proposed system, and their faults.
What was chosen was a compromise. It allowed reasonable performance at a price that people would be able to afford to buy televisions. Some wanted to use AM for the audio, and FM for video. Others wanted to use AM for video, instead of Vestigial Sideband which had the same signal quality, with most of one sideband being suppressed, but still had the carrier to make detection easy.. Also, the original TVs used two separate receivers. It was the concept of Intercarrier reception that simplified operation to where anyone could select a channel. I don't miss dirty contacts, cracked wafer switches or worn out channel strips in VHF tuners. I repaired too many TV tuners back in the '70s, including making a replacement tuner for a Conrac Demod for a military TV station. There were no spares to be had, and a custom built replacement from? Sarks-Tarzan, (The OEM) would have cost more than a newer model Demod.
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Your friend is simply wrong. There were no math errors. A small shift was necessary to accommodate a spectral interleaving of the chroma and luminance signals with practical (cheap) circuits. The shift in line and frame rates was small enough to permit backwards compatibility with monochrome sets.
¡ª Tom Sent from my iThing; please forgive the typos and brevity
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On Mar 31, 2023, at 04:56, Jeff Green <Jeff.L.Green1970@...> wrote:
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He also insists, and showed me the math, the engineers made some simple math errors that resulted in the vertical being 1/2 of 59.94Hz.
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Great Story. I enjoyed it. ? I too have enjoyed my long-term scar of four adjacent pins full of 150V Low Voltage. Four 0.25¡± evenly spaced 2 inch long scars on my wrist. ? The worst shock I ever received was an arc from an HV Anode Button through my Heathkit HV Probe, through my arm, down my body, through my knee, through their carpet, into their concrete floor. I was fixing a neighbor¡¯s TV, they later told me they asked me to fix it so that they could sell it - crap. It was a bad Power Supply Bulk Capacitor that had failed. I have no idea how it developed a voltage that high. ? Ross ?
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From: [email protected] < [email protected]> On Behalf Of Chuck Moore via groups.io Sent: Thursday, March 30, 2023 11:50 PM To: [email protected]Subject: Re: [Test Equipment Design & Construction] Some comments on calibrating a Tektronix CFC250 100MHz frequency counter. ? It was surprising the mechanical spinning disk system ever made it to market. The imagery was not bad but having the outer disk speed was fairly fast. And the drive motors were not exactly quiet. A lot of female customers complained about the noise from the disk and the mechanical vibration that frequently occurred in the flyback transformer at 17,734 Hertz. Yeah women could hear it.
Another wart in early three gun color crt technology was adjustment of the screen purity for round crts. Early color crts used steel bells which flared to matched the crt face plate. Unlike later crts which used layers of aquadag to form the high voltage filter capacitor, the metal bell crts used doorknob capacitors and the whole crt bell was run at about 22 KV. The purity was adjusted by rotating magnets positioned around the edge of glass faceplate adjacent to the crt bell. The last one I worked on had 12 magnets and you best be extra careful or the shop owner would get a phone call about the foul mouth service tech sent to her home. getting a jolt of 22 KV while adjusting purity was a right of passage in the 50's.? And those doorknob capacitors stored a grunch of current. The later glass bell crts which used the conductive aquadag to form the HV Filter capacitor did not hurt as much when you accidentally came in contact. It still hurt, but not like a high Q doorknob dumping every last electron unimpeded into a finger tip. Aye Chihauhua!
Then there were the pets. In particular cats, and especially Siamese cats. I had removed one (a Siamese cat) from the inside of a customer's console color television several times while serving the set with the back off. Motorla used nickel plated steel pins inserted into the printed circuit board in that particualr model, then wrapped the interconnecting wires around the pins using wire wrap techniques. And they stuck straight up, just waiting for a careless finger. Nothing like impaling your finger tip on one and feeling the crude finish drag against the inside of your finger as you pulled back. Back to the cat. I asked the owner to help keep him away from the set while I had the back off, as I feared he would be injured. I could just imagine the damage that bugger could do if he stepped on the bed of those wire wrap terminals in the chassis. She removed the cat and I proceeded to change out a tube here and there. I had just inserted one tube, plugged in the ac power (cheater) cord to power the set up and turned to reach into the tube caddy for a long skinny screwdriver, when there was a squall from a creature in pain. The cat had returned, crawled in with my back turned and apparently found a B Boost (about 800 volt DC) terminal. I saw a blur as the cat left at light speed, and just sat speechless over the carnage the cat had inflicted on that poor television. IF Cans, coil forms, laid over broken, tube pins were bent so badly I feared straightening them. Several wires were torn loose. The cat survived, but he did not intrude again during that visit. And I explained to an insurance agent how the customer's cat destroyed a color television.
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Most people forget or ignore that it was interlaced video, with a two field, 29,97 Hz frame rate.That throws off their idea of how the math worked.
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Jeff,
in the way back bad old days when networks (CBS, ABC, NBC) actually did live broadcast you could use their color burst as a frequency reference (subject to several caveats though) because they generated the burst signal from a Cesium Beam standard. NBS (well NIST now) used to publish a bulletin weekly that showed many of the LF radio stations including WWV and the broadcast networks calculated frequency error from, if memory serves, the Navel Observatory. ?In our lab we used Jim Creek Washington on 18.6KHz for our in house standard. Ahhhhh the Fluke 207 what a device
anyway more trivia found on Silicon Slough
Steve
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The original specs were replaced by the PDf you referenced. A lot of early history of radio and TV never made it onto the FCC website because it wasn't needed. A better search is History of NTSC.
My final comment is to download and read the National Semiconductor LM1882 datasheet. It is a single chip NTSC Sync Generator that uses a 14.318,180 MHz crystal. It was used in many TV cameras and pieces of industrial video equipment The LM1881 could recover sync data and be used with the LM1882 to regenerate sync, as needed to sync multiple video inputs.
The original datasheets are in some '80s databooks. The later programmable versions dwell on programming, not the math and waveforms.
My initial use of, and repairing HP and Tektronix was due to working daily to rebuild a very run down military TV station in the '70s. No outside support, and no internet to offer tips so I read every equipment manual, cover to cover starting with a defective Tek scope. As far as I could find out, it was the only one on base since TDY techs brought their equipment when they did repairs to the limited electronics at that base. That will soon be 50 years ago. Prior to this, I had mostly only seen TV shop grade test equipment that was old and in bad shape.
Can we let this thread die?
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I didn't mean to start the thread drift on the intricacies of NTSC timing. I thought others might have test equipment with the National Semiconductor MM5369AAN 3.58MHz to 60Hz chip and my experience might help them.
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I honestly don't understand the subtleties of NTSC or any analog TV standard well enough to argue and I shouldn't have commented beyond 'Never The Same Color.'
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I will say that I checked several references and all say color burst is 3.579545
¡À 0.0003%
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I think this is the single best reference I found today:
I'm pretty good at research but I wasted an hour trying to dig around the FCC online web page for the original NTSC specifications but gave up. I suspect the information is there but I wasn't able to phrase my search properly.
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Michael A. Terrell