15Hz NBTV? Heavens forbid!

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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Thu Jun 08, 2023 7:31 pm

Beware! They are colour standards convertors, NOT line/frame rate convertors! I was fooled many years ago. They convert PAL into NTSC or the other way. They DO NOT convert convert 525 to 625 or the other way. i.e. they convert the colour information (crudely) but NOT the frame or line structure. Useful (maybe) in countries that have PAL on 525 or NTSC on 625. Mainly South American countries.

Think thus, PAL does NOT mean 625 lines, NTSC does NOT mean 525 lines. It's the colour encoding standard which has almost NOTHING to do with lines and frames. It's assumed that NTSC=525 lines, and PAL=625 lines. But it doesn't have to be so. These convertors are sold to the unwary - like I was many years ago. They're basically useless to most of us, that's assuming they work at all...I bought one in Hong Kong when I lived there, useless. In the trash the next day.

Recall tests were conducted using NTSC on 405-lines in the UK, the results were apparently quite good, but 625 was on the way and PAL was chosen. Thankfully.

Unless you're in South America (The Continent) don't buy one. They're useless - someone tell me otherwise...

Steve A.

Remember, as so many might, and do, think otherwise...PAL does NOT mean 625 lines, NTSC does NOT mean 525 lines. It's a colour definition standard, not a line or frame-rate definition...although often closely linked to their respective standards and implemetations...
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Re: 15Hz NBTV? Heavens forbid!

Postby Harry Dalek » Mon Jun 12, 2023 5:22 pm

I noticed my son had some thing similar but 625 line to HDMI the other way could of been useful for testing since its small only for the B/W signal but any case i still have a true systems converter 525 line to 625 line visa versa NTSC to PAL and a does a test card i might use on my project testing the LM1881 i forgot i ordered 8 of them when i was down to one or 2 a while back working on the 405 line magnetic deflected CRT project .
I noticed reading the data on the LM1881 the R set resistor that changes its range

The LM1881 to be adjusted for source signals with line scan frequencies differing from 15.734 kHz. Four
major sync signals are available from the I/C; composite sync including both horizontal and vertical scan timing
information; a vertical sync pulse; a burst gate or back porch clamp pulse; and an odd and even output.
Has a top range line frequency of 150khz i wonder what the bottom range is .
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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Mon Jun 12, 2023 6:11 pm

Harry Dalek wrote:...I wonder what the bottom range is .

...I suspect not that much lower, plus it expects equalising pulses and broad pulses within the vertical period. I have used this chip many times for standard 525/625 sources, and it works well. But using it for NBTV I would guess it's a non-starter, as we have no pulses at all within the frame/field sync period. Someone say I'm wrong!

I did do an item which appeared in the NBTVA newsletter some 13 years ago, which predicted where the 'missing pulse' would be. It worked quite well (If I may say so), But it seemingly generated zero interest, so I gave up on it. Now I understand why many give up on creating things like a YouTube channel, or any other form of publishing. I've thought about creating a YouTube channel many times, and not just for NBTV, and thought, "Why bother?" Many others that do create a YouTube channel seem to reach the same conclusion fairly quickly.

However, there are others who are quite successful, I guess they get the 'formula' just right.

Fig 6.jpg
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Fig 4A Colour.gif
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Yellow trace is standard NBTV input signal.

Cyan trace is standard NBTV sync detection.

Magenta trace is Micro-generated frame sync.

Green trace is the combined uninterrupted 400Hz line sync output.

..it works from less than 300Hz to over 500Hz, in exactly the same manner...automatically, It guesses where the frame sync should be, based on the preceding 30 lines, an averaging technique, no 'tuning' required.

A 300Hz line-rate NBTV input...

Fig 3A Colour.gif
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A 500Hz line-rate NBTV input...

Fig 5A Colour.gif
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Steve A.
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Re: 15Hz NBTV? Heavens forbid!

Postby Harry Dalek » Mon Jun 12, 2023 9:23 pm

Steve Anderson wrote:...I suspect not that much lower, plus it expects equalising pulses and broad pulses within the vertical period. I have used this chip many times for standard 525/625 sources, and it works well. But using it for NBTV I would guess it's a non-starter, as we have no pulses at all within the frame/field sync period. Someone say I'm wrong!

I did do an item which appeared in the NBTVA newsletter some 13 years ago, which predicted where the 'missing pulse' would be. It worked quite well (If I may say so), But it seemingly generated zero interest, so I gave up on it. Now I understand why many give up on creating things like a YouTube channel, or any other form of publishing. I've thought about creating a YouTube channel many times, and not just for NBTV, and thought, "Why bother?" Many others that do create a YouTube channel seem to reach the same conclusion fairly quickly.

However, there are others who are quite successful, I guess they get the 'formula' just right.


Steve A.


I think if the chip is programmed one some one like me will go great idea but i can't make that so that sort of puts you off not that there is no interest just some people have a limit in what they are willing to try ,there are valve people people that just like CRTS and others the mechanical side to NBTV that sort of thing .
The idea is similar to how you designed the Anderson monitor syncing part monostables for 32 line ...... with selector switching caps and resistors changed for the ramp oscillators the devil monitor and the Beast monitor the things synced 15 line to 240 and 12.5 25 50 hz also other systems like i showed 240 line at 2 hz it was very good ! So i have made use of your work many times .
Richard is very good at the you tube channel showing he's projects and talk and explain and show the design so does get it right .

I was not thinking of using the Lm1881 for 32 line might be pushing it but if it just did the line sync i would be impressed i was thinking more above 100 line i have try it on 240 line 25 so i know it works down to that .
With FreeNBTV you can add a frame pulse to your video not standard but why do we have to stick to standard who made that rule up the club i suppose may be we need to change that rule ! no frame pulse is one way to do it but not the best way to do it ...what i am getting at going off club standard can be fun too .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Tue Jun 13, 2023 12:53 pm

Harry Dalek wrote:..but why do we have to stick to standard who made that rule up the club i suppose may be we need to change that rule ! no frame pulse is one way to do it but not the best way to do it ...what i am getting at going off club standard can be fun too .

I assume the reason for the 'missing pulse' frame sync is partly historical, and partly technical. The historical and technical reasons are somewhat intertwined. The resurgence of the interest in NBTV was maybe in the 60s or 70s. The only practical method of recording/storing NBTV signals then was primarily open-reel tape recorders, or in time, cassettes. The bandwidth of both domestically was maybe 10kHz, often less in those days. The low-frequency performance was similarly 'not so good'. (read awful).

Devoting a whole line to frame sync meant losing around 3% of 'picture time' which was felt to be wasteful. Not having a line sync when one was expected meant this was frame sync.

The way the unit works in my posting above regenerates the missing sync which also acts as a frame sync. BUT, it does require a good clean signal path and to a degree reasonably accurate hole-drilling if using a disc camera. I doubt it would be useable on the noisy HF amateur bands, especially with their limited audio bandwidth.

Once you get to 100 or more lines (e.g. early SSTV with 120/128 lines), the loss of 1 line in 100 or more is 'acceptable'. Also, SSTV being based on an FM subcarrier the low-frequency problem goes away at the expense of reduced high-frequency video components. Nothing is ever free!

Here we are more than two decades into the 21st Century and there is still no sane and simple alternative to the 'missing sync' method whilst keeping things in the analogue domain, and at least some semblance to the origins of analogue TV.

Steve A.
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Re: 15Hz NBTV? Heavens forbid!

Postby Harry Dalek » Tue Jun 13, 2023 4:21 pm

Steve Anderson wrote:I assume the reason for the 'missing pulse' frame sync is partly historical, and partly technical. The historical and technical reasons are somewhat intertwined. The resurgence of the interest in NBTV was maybe in the 60s or 70s. The only practical method of recording/storing NBTV signals then was primarily open-reel tape recorders, or in time, cassettes. The bandwidth of both domestically was maybe 10kHz, often less in those days. The low-frequency performance was similarly 'not so good'. (read awful).




The first to try television magnetic recording was Mihaly's recordings on wire 1929 idea shown below i have no idea if the idea and results were better than Baird's mechanical recordings .
125793086_10225256162530765_7875870479809197711_n.jpg


They could of tried phonoVision or Mr Plew's Mechanical similar idea to Bairds but he only did stills ......
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But what gets me is why they never tried optical recording on movie films sound track which came in around mid 20s it would of been better than magnetic and mechanical recording not only that they could of filmed the experiment in HD at the same time ! I suppose the result might be similar to the below idea

76652008_10221473662770635_8681272113841045504_n.jpg
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Devoting a whole line to frame sync meant losing around 3% of 'picture time' which was felt to be wasteful. Not having a line sync when one was expected meant this was frame sync.


I can see why they didn't want it ,but its a wonder there were not 2 camps going with and not going with the framing sync pulse .

The way the unit works in my posting above regenerates the missing sync which also acts as a frame sync. BUT, it does require a good clean signal path and to a degree reasonably accurate hole-drilling if using a disc camera. I doubt it would be useable on the noisy HF amateur bands, especially with their limited audio bandwidth.

I must admit i have never come across NBTV on SW for some reason never took off and every one went with SSTV ,got you it would of been nice if some one could try it .

Once you get to 100 or more lines (e.g. early SSTV with 120/128 lines), the loss of 1 line in 100 or more is 'acceptable'. Also, SSTV being based on an FM subcarrier the low-frequency problem goes away at the expense of reduced high-frequency video components. Nothing is ever free!


OH yes as in Digital Television is great and the expense is either its wonderful picture or nothing and narrower bandwidth a time delay processing the signal .
Least with analog if its signal is poor you can see the result and its more speeder seeing the results ,when we had both digital and analog it was so noticeable if you viewed both at the same time .

Here we are more than two decades into the 21st Century and there is still no sane and simple alternative to the 'missing sync' method whilst keeping things in the analogue domain, and at least some semblance to the origins of analogue TV.
[/quote]

Well we want to keep it Analog it might of gone in the real world for the fussy fickle majority but i like it .
Last edited by Harry Dalek on Tue Jun 13, 2023 5:02 pm, edited 1 time in total.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Tue Jun 13, 2023 4:58 pm

I've been thinking of using GPS/GNSS for sync pulses - it's hard to get a better timing standard, and they're within a few (20-30) nano-seconds of each other wherever you may be on this planet.

Why? They're so accurate syncs wouldn't need transmitting! Video with no sync pulses...not exactly true, just a one-off 'reference point'. Ionospheric propagation may be an issue though depending on frequencies used for the video signal. Cables, fibres and frequencies unaffected by atmospheric conditions would be more stable and useful...possibly? 'Sort of' thinking aloud...

Steve A.

The more I think on this the easier it's becoming!!
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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Tue Jun 13, 2023 5:45 pm

Harry Dalek wrote:I must admit i have never come across NBTV on SW for some reason never took off and every one went with SSTV ,got you it would of been nice if some one could try

I believe there was a NBTV 'net' on 3.5MHz years ago on certain days and times. What happened to it I don't know. Primarily in Northern Europe I think...whether it was a form of on-air 'discussion group' and/or NBTV was transmitted I also don't know...

It would be interesting to know how many members here have a current Amateur Radio Licence - of any sort. I did many years ago in the UK, but VHF/UHF only, 2m, 70cm and upwards. But not any more...

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Re: 15Hz NBTV? Heavens forbid!

Postby Harry Dalek » Tue Jun 13, 2023 8:13 pm

Steve Anderson wrote:I've been thinking of using GPS/GNSS for sync pulses - it's hard to get a better timing standard, and they're within a few (20-30) nano-seconds of each other wherever you may be on this planet.

Why? They're so accurate syncs wouldn't need transmitting! Video with no sync pulses...not exactly true, just a one-off 'reference point'. Ionospheric propagation may be an issue though depending on frequencies used for the video signal. Cables, fibres and frequencies unaffected by atmospheric conditions would be more stable and useful...possibly? 'Sort of' thinking aloud...

Steve A.

The more I think on this the easier it's becoming!!


When going for a similar idea not using the sync pulses at all but using a crystal as the clock the problem i found was image drift and line start position worse on the framing and it speeds up this was 32 line on 64 line twice as bad a reset button you could get the line close to where it should be with a few go's but with closer to the HZ accurate timing i can't see why it wouldn't work this below was close but timing still not perfect .

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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Wed Jun 14, 2023 11:23 am

I put together a system some years ago where there was just a frame sync, no line syncs. It worked very well (closed-circuit). It was a 48-line system at 12.5fps with standard scanning (left-right/top-bottom). It worked well. I calculated the timing error (as none was visible) which turned out to be a small fraction of one pixel in the whole frame. I assumed the crystals used were really cheap with a +/-100ppm 'accuracy'. (i.e. very poor for a crystal).

Using GPS/GNSS it should be far, far better, especially if both ends of the circuit use the same reference. I wonder if the various GNSS systems (GPS, Europa, GLONASS etc.) are locked together? If a GPS receiver can process more than one system simultaneously (most today can and do) which system should it use if they are even slightly different in timing?

Years ago a good local source of accurate timing/frequency was the sync pulses within standard 525/625 analogue TV off-air. The TV station SPG (Sync Pulse Generator) had to have (by law in the UK strangely) an accuracy of +/- 1Hz for the colour subcarrier at 4.43MHz (0.226ppm). All other timings/pulses were derived from that or a multiple. When GPS came along they were locked to GPS and thus became as good, long-term.

Steve A.

In many countries the 50/60Hz power mains supply is also locked to some atomic reference. Once you filter out the rubbish that gets superimposed on it, it's also a good long-term source of accurate frequency.
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Re: 15Hz NBTV? Heavens forbid!

Postby Harry Dalek » Wed Jun 14, 2023 5:24 pm

Steve Anderson wrote:I put together a system some years ago where there was just a frame sync, no line syncs. It worked very well (closed-circuit). It was a 48-line system at 12.5fps with standard scanning (left-right/top-bottom). It worked well. I calculated the timing error (as none was visible) which turned out to be a small fraction of one pixel in the whole frame. I assumed the crystals used were really cheap with a +/-100ppm 'accuracy'. (i.e. very poor for a crystal).


Tweaking the crystal oscillator a few Hz is possible i don't think i did for the above looking at what i used ..Your go sounds interesting was that posted any where ?
Using GPS/GNSS it should be far, far better, especially if both ends of the circuit use the same reference. I wonder if the various GNSS systems (GPS, Europa, GLONASS etc.) are locked together? If a GPS receiver can process more than one system simultaneously (most today can and do) which system should it use if they are even slightly different in timing?


I am not familiar with the what GPS so i googled ! so its the carrier L1, at 1575.42 MHz, and L2, at 1227.6 MHz and you are going to divide this down down yes .

Years ago a good local source of accurate timing/frequency was the sync pulses within standard 525/625 analogue TV off-air. The TV station SPG (Sync Pulse Generator) had to have (by law in the UK strangely) an accuracy of +/- 1Hz for the colour subcarrier at 4.43MHz (0.226ppm). All other timings/pulses were derived from that or a multiple. When GPS came along they were locked to GPS and thus became as good, long-term.

Steve A.


Not heard that before interesting i am not sure we had that rule here but i suppose you go with what's accurate .

In many countries the 50/60Hz power mains supply is also locked to some atomic reference. Once you filter out the rubbish that gets superimposed on it, it's also a good long-term source of accurate frequency.

[/quote]

That's something i have never tested to see if it swings i would of thought it did since its mechanical and the voltage go's up and down like a yoyo here. So the mains can be that stable that's surprising !
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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Wed Jun 14, 2023 7:37 pm

The GPS receiver I use outputs both NMEA data and the 1PPS signal. It has been superseded since, but basically with the same functionality.

SepQSTQLG1 (2).png
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It has a large ground-plane outside the 'patch antenna' which gives it a significant boost in sensitivity. Now has been replaced with another version from the same supplier, but mine keeps going after almost ten years...As it's outside it's inside a very waterproof box...I submerged the box by 1m for a month with the cable gland and cable to check for leaks. After one month submerged, not a drop inside!

I also added TVS diodes to both the power and data leads to hopefully reduce the chance of a nearby thunderstorm 'ZAP' having any effect. So far so good.

The next day: I forgot to add, it's powered on (and has been continuously for 10 years) 24/7. Back-up in the event of power failure is provided via a 7Ah/12V lead-acid battery, that's enough for well over a week, the receiver uses about 35mA including the 7805 regulator for it. The battery is inside the house so it doesn't have to endure the elements outside. I intend to change the battery with a LiPo arrangement when this lead-acid one shows signs of expiring...that should be early next year I expect, Lead-Acid batteries only last about three years in this climate.

Steve A.

Although the owner of the business is an on-line friend, I have no affiliation with his business...
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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Thu Jun 15, 2023 6:05 pm

Where did this thread start? Oh yes, 15Hz NBTV. One of the reasons I'm considering 15Hz at all is most computer displays are geared around 30, 60 frames/sec or some multiple thereof. As the trend seems to be going in that direction it might be wise to consider it, for better or for worse. There are a few odd ones at 56Hz and the like, but let's ignore those. I imagine in time 25Hz or a multiple thereof is going to vanish. Like it or lump it, that's the direction things seem to be heading in the analogue world. VGA is analogue after all and surely will be replaced (already has?) by a digital format.

While there's this 'overlap' between the analogue and digital world we may as well take advantage of it, even if maybe it is short-lived.

Brewing in my wonky mind is a 60/30/15Hz NBTV system, which many might view as 'going against the grain' of NBTV being based on a derivative of the European mains frequency. The reasons for which are really of no significance these days, except maybe for historical reasons. In those countries that use 50Hz, it's not going to go away or change in our lifetime (youngsters included). However today we freely mix all sorts of standards with aplomb. The mains power frequency is no longer a factor, though it very much was 'back then'...including early all-electronic TV.

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Re: 15Hz NBTV? Heavens forbid!

Postby Harry Dalek » Sat Jun 17, 2023 2:20 pm

I forgot to mention my digital cameras output video i could be wrong but from memory both Pal and NTSC if you come across something in your travels .
I also got out my systems converter thankfully still operating come in useful testing the LM1881
https://www.converters.tv/pal_to_pal/NT ... 0-/18.html

Testing the colour bar below ,i had to macgyver the power cable centre socket is negative most supplies are positive and misplaced the original .

DSCN8674.JPG
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DSCN8679.JPG
DSCN8680.JPG
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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Tue Jun 20, 2023 2:09 pm

Interesting 'thing' Harry, though the chroma subcarrier (first photo) looks quite low for colour bars.

!5Hz NBTV? ... As time goes on the old 25/50Hz TV line/frame rates are disappearing. Looking through the list of VESA monitor standards there are none, really none, based on 25Hz or 50Hz, the odd 75Hz rate, but few. But the vast majority support 60Hz and more at formats from 640x350 up to at least 1920x1440, probably more these days.

So maybe 15Hz NBTV isn't so daft an idea after all? A 20% increase in line/frame rates. OK, sometimes the numbers and timings might not be so 'round', but it is just a number after all.

Maybe this is a sign of things to come? i.e. We have more PC monitors in this house than TVs. I watch more audio/visual material on a PC monitor rather than what could be called a 'TV'...and the audio is far better too...mainly down the the small crappy speakers used in TVs.

I am looking into an up-converter from 15Hz NBTV and SSTV to 60Hz 800x600 VGA. The 50/60Hz thing really doesn't apply to SSTV as it's really just a sequence of stills.

Steve A.

I may also have a go at 12.5Hz NBTV to the above VGA standard, but there may be some visible artifacts from the conversion. There could be some form of 'heterodyning' (flicker at 2.5Hz) between the 12.5Hz and 15Hz/60Hz frame rates...some form of interpolation may help though....More anon...I'm beginning to regret living in a 50Hz country...and my origin country....but it's just numbers, what the heck!
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