15Hz NBTV? Heavens forbid!

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15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Thu Jun 01, 2023 5:49 pm

Many might consider the thought of a 15Hz frame-rate NBTV signal as heretic. Going against the almighty-given 12.5Hz frame-rate. It does require a 20% increase in bandwidth all other things being equal, but that really isn't (or shouldn't be) an issue these days. On the plus side it does to a limited extent reduce the effect of flicker.

Now, the reason I raise this matter is that there are many 60Hz monochrome (and colour) 'board' cameras 'out there', there are few, very few, 50Hz versions...someone tell me I'm wrong...please!!..

Conversion from 60Hz to 50Hz is possible, and likewise 15Hz to 12.5Hz, but if that hassle can be avoided, so much the better...I do not have any 50Hz cameras even though I live in a 50Hz country, those I do have are all 60Hz irrespective of supply frequency...most are DC-powered anyway and don't use the mains frequency as any sort of reference...(which is a good thing anyway)...

A thought as a result of the above last sentence...if using a GPS reference source or even a local crystal oscillator you shouldn't need line-sync pulses. Somewhere in the past I did this with only a crystal-derived frame sync, no GPS and no line syncs...it worked fine...if using GPS you shouldn't even need frame sync....though you may need a 'framing' control, but once set you should be able to forget it...though if you move locations that might need some adjustment...not sure...probably not...well maybe..."Yours undecided of Bangkok"....remember those type of letters broadcast on BBC Radio? I do...do they they still?...somehow I doubt it...I'm not in the UK anymore so I don't know, though I could listen to the Internet based version, I just don't...

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

Postby Harry Dalek » Sat Jun 03, 2023 10:32 am

We can make this on FreeNBTV i suppose a current nipkow monitor run a little faster to display .
Not that far off change things for a CRT either my devil and beast monitors could display it right now .
I rather like the off NBTV standard makes the hobby more interesting ,
I see there are a lot of views on the post but it would nice to give Steve a reply on he's posting effort guys .
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 » Sat Jun 03, 2023 1:06 pm

True, a basic Nipkow-style disc would have to spin at 900RPM as opposed to the more usual 750RPM, most other things much the same.

For an electronically-based display it makes little difference, timings need to be 20% faster, but nothing significant otherwise.

In the same manner, an electronic device that converts 525 to 15Hz NBTV would be much the same as one that converts 625 to 12.5Hz, just different timings. It would be quite easy to get one device to do both.

But 'cross-standard' isn't quite so easy, i.e. 525 to 12.5Hz or 625 to 15Hz. Not impossible, but quite a complex device would result. Quite a challenge really...similar to the conversion in years past between 405, 525 and 625 in any combination or direction, with or without colour...

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Re: 15Hz NBTV? Heavens forbid!

Postby Harry Dalek » Sat Jun 03, 2023 1:46 pm

Steve Anderson wrote:
But 'cross-standard' isn't quite so easy, i.e. 525 to 12.5Hz or 625 to 15Hz. Not impossible, but quite a complex device would result. Quite a challenge really...similar to the conversion in years past between 405, 525 and 625 in any combination or direction, with or without colour...

Steve A.


Yes perhaps not building from scratch but converting gear that would be a touch harder ,not easy to get those standards in the first place monitor a bit easier ...Yep a system converter my head hurt's ! I still have a 525 line to 625 line colour system converter i think 2 NTSC colour frequencies from memory hardy used these days now a dinosaur but bloody complex little thing .
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 » Sun Jun 04, 2023 1:25 pm

My thinking is to do a 525 to 32-line/15fps standards convertor as I have a source of US standard 525 signals, a small 'board' camera. Assuming that works it should be a relatively simple exercise to adapt it to a 625/12.5 version, though the only source of 625 I have is an output on our set-top box in the living room. Somewhat inconvenient as it's on a different floor to my workshop/office and the cable-run would be awkward and around 25m. I'll think of a solution.

One component issue could be the A-D required. The CA3306 has been the device of choice for decades but it's hard to find these days and probably expensive [1]. An alternative is the AD7822 which is 8-bit as opposed to the 6-bit CA3306 and just capable of the sample rate required. However, I bought some years ago in DIL packaging, now you may have to shop around as most suppliers only have them in SMD versions. An alternative needs to be found, and at a sane price!

Steve A.

[1] Though I do have a local (Thailand) source of the CA3306 in DIL packaging, around 60 in stock at around GBP3.00 each, made by Harris, Intersil or RCA. I think, once gone, that's it!

Another chip that's getting harder to find in DIL packaging is the LM1881 sync separator, Cricklewood (UK) have them now, but how many? The same Thai supplier mentioned above has 1000+ in stock if UK sources dry up. Around GBP2.20 each in one-off quantities. The LM1881 has been superseded by the LMH1980 which handles HD and SD, but SMD (VSSOP) only.

LMH1980 TI.pdf
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Re: 15Hz NBTV? Heavens forbid!

Postby Harry Dalek » Mon Jun 05, 2023 6:33 pm

Steve Anderson wrote:My thinking is to do a 525 to 32-line/15fps standards convertor as I have a source of US standard 525 signals, a small 'board' camera. Assuming that works it should be a relatively simple exercise to adapt it to a 625/12.5 version, though the only source of 625 I have is an output on our set-top box in the living room. Somewhat inconvenient as it's on a different floor to my workshop/office and the cable-run would be awkward and around 25m. I'll think of a solution.


Well perhaps on the 625 line an old camera or VCR ,there are old PC video cards that output it i think i still have one in my draw and as in my project my gaming PC video card that is one of the many it can output.

One component issue could be the A-D required. The CA3306 has been the device of choice for decades but it's hard to find these days and probably expensive [1]. An alternative is the AD7822 which is 8-bit as opposed to the 6-bit CA3306 and just capable of the sample rate required. However, I bought some years ago in DIL packaging, now you may have to shop around as most suppliers only have them in SMD versions. An alternative needs to be found, and at a sane price!

Steve A.


Yes old IC's are hard to get these days some times a Valve is easer to find .

[1] Though I do have a local (Thailand) source of the CA3306 in DIL packaging, around 60 in stock at around GBP3.00 each, made by Harris, Intersil or RCA. I think, once gone, that's it!


Not played around with A/D converters only other way around

Another chip that's getting harder to find in DIL packaging is the LM1881 sync separator, Cricklewood (UK) have them now, but how many? The same Thai supplier mentioned above has 1000+ in stock if UK sources dry up. Around GBP2.20 each in one-off quantities. The LM1881 has been superseded by the LMH1980 which handles HD and SD, but SMD (VSSOP) only.

LMH1980 TI.pdf
[/quote]

Yes also something a bit old for interest to many these days ,i have 2 i think at least one working it has a very wide range not just 625 or 525 line sync i tried it down to 240 and use it on 405 line very useful for us nice little sync separator. I looked at the new version very similar bit more wiring to it i think ,pity only comes in the tiny package i can just manage to solder these things on a little adapter board not easy with my eyes ..i use a copper wire wrapped around the iron tip and use the end of the copper wire as the soldering tip much finer that trying to use a the iron tip that's to large to work with.
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 06, 2023 11:33 am

Harry Dalek wrote:Well perhaps on the 625 line an old camera or VCR ,there are old PC video cards that output it i think i still have one in my draw and as in my project my gaming PC video card that is one of the many it can output.

Nope, no other sources of 625 here except the set-top box, no VCR, no Camcorder, no DVD player, nothing. They all died (as expected) years ago, I'm not sure the TV/monitor in the living room has a 625 input, though I know the TV in my office/workshop does, both 525 and 625, PAL or NTSC.

I could make a static 625 source using a PIC device, a crude Test Card type of thing. A modified version of the SPG used in the SSTV-625 up-convertor. It's monochrome only, but that's all I'm interested in anyway. Also, most test cards were monochrome except for the centre circle (BBC style, Test Card F) and maybe some primary and complimentary coulours around the edge. Quite easy to do in component video (YUV, Y,Pb,Pr etc.), but coding properly into PAL or NTSC is another thing! Especially considering how little it would be used.

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Re: 15Hz NBTV? Heavens forbid!

Postby Harry Dalek » Tue Jun 06, 2023 4:27 pm

"Steve Anderson"
Nope, no other sources of 625 here except the set-top box, no VCR, no Camcorder, no DVD player, nothing. They all died (as expected) years ago, I'm not sure the TV/monitor in the living room has a 625 input, though I know the TV in my office/workshop does, both 525 and 625, PAL or NTSC.

I could make a static 625 source using a PIC device, a crude Test Card type of thing. A modified version of the SPG used in the SSTV-625 up-convertor. It's monochrome only, but that's all I'm interested in anyway. Also, most test cards were monochrome except for the centre circle (BBC style, Test Card F) and maybe some primary and complimentary coulours around the edge. Quite easy to do in component video (YUV, Y,Pb,Pr etc.), but coding properly into PAL or NTSC is another thing! Especially considering how little it would be used.

Steve A.


I still have a fair few things that do 625 line but yes as you say just make a simple test card generator ,i am a great one watching what's going free on the side of the road , nothing like that your neck of the woods or a reuse shop old play station x box a tiny dvd player would be a good thing to look for plays the disc or not you would get a test card screen on power up and they are tiny or were . Depends if you are bothered to build if some thing like that is about no one wants .
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 06, 2023 5:45 pm

One problem I would have is I have no audio CDs or DVDs anymore, I find once I've seen a movie once or twice, I don't need or want to see it again. As for audio, either rip it yourself or download it...I have a NAS so hopefully I'm unlikely to lose anything.

The issue here, and as I suspected quite some years ago, is the hardware that outputs 525/625 is vanishing, or already has. Even component analogue (YUV etc.) is becoming rare. PC monitors with D-type ('VGA') or DVI inputs are also becoming scarce. Such is 'progress'.

Steve A.

Once I've done this, many years in gestation, a VGA (maybe DVI, HDMI or Display Port version, they are very similar) is on the horizon.
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Re: 15Hz NBTV? Heavens forbid!

Postby M3DVQ » Tue Jun 06, 2023 11:36 pm

If you can manage to get hold of a raspberry pi they're a small and convenient source of 625 and 525 line composite (the SBC versions, not the Pi 400 as that omits the analogue outputs)
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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Wed Jun 07, 2023 10:54 am

Thanks for the info. I wasn't aware that some Pi versions put out composite video, I assumed it was VGA/HDMI or something else only.

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Re: 15Hz NBTV? Heavens forbid!

Postby M3DVQ » Thu Jun 08, 2023 2:30 am

The original model has a phono socket and separate headphone jack but on later models it was all moved to a single TRRS jack. The "zero" boards have composite too but not on a populated connector.

They all have HDMI or mini HDMI which is what almost everyone actually uses unless using them specifically for analogue TV playout like I am, since using a modern OS via a 576i display is pretty miserable!
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Re: 15Hz NBTV? Heavens forbid!

Postby Steve Anderson » Thu Jun 08, 2023 2:22 pm

Well, I doubt I'll buy a Pi just to get a source of 625, I do have one source already, but as noted it's not in a convenient location and cannot be moved due to the incoming fibre termination point. I may be able to borrow something from a friend anyway - yes, I do have some!

Finding a source of a 625 camera would be the answer, but they're getting rare these days. I did spend some time on-line trying to find a supplier to no avail yesterday. Quasar Electronics in the UK used to have them, but it appears they've gone out of business... I did find a few with either digital outputs or VGA-style outputs (RGB, 640x480), they may be a possibility. They would remove the need for a filter to suppress the PAL subcarrier, though one is still needed for anti-aliasing, though somewhat simpler.

But, most VGA modes are not 25/50Hz friendly! Back to square one!

Steve A.

I think for the time being I'm going to have to stick with 30/60Hz inputs and a 15Hz NBTV output. Generally there's little difference to to a 25/50Hz source and a 12.5Hz output. Mostly just timing adjustments.
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Re: 15Hz NBTV? Heavens forbid!

Postby Harry Dalek » Thu Jun 08, 2023 6:36 pm

Hi Steve i was looking on ebay if they still made something like i ended up buying in 1990 things have improved i will add to this if i find some thing else ..this is very small and cheap
https://www.ebay.com.au/itm/15528491603 ... BMuLjknpNi

or
https://www.aliexpress.com/i/32349218573.html

I was looking t this and thinking you really need the above !
https://www.icce.rug.nl/~soundscapes/VO ... cies.shtml
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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 Harry Dalek » Thu Jun 08, 2023 7:17 pm

Steve they also have this HDMI to Pal or NTSC so you could out put your PC to pal or NTSC
https://www.temu.com/au/moon_subject/n9 ... f-551e2358
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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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