NBTV/SSTV-625 Up Converter MkIII

Where it all started as far as most are concerned and saw heavy use from the 60s through to the 80s. Colour and Hi-res modes have unfortunately pushed this system into the backwaters of SSTV. Time to resurrect interest in this simple analogue system.

Re: NBTV/SSTV-625 Up Converter MkIII

Postby Klaas Robers » Fri Nov 22, 2019 11:47 pm

Steve, your problem is: time. There should be a decoupling of time for the FM-demodulation and the storage into the frame memory. That is also more or less the problem that I encountered one year (?) ago.

Let me separate the two processes:
1. There is a process that measures the amount of time between two zero crossings of the (limited) input signal. The result is converted into a "grey value number". This is a process that is synchronous to the input signal wave form. The latest grey value number is for some time the "voltage" of the video signal. This is until the next zero crossing of the input signal occurs.

2. The second process is a process that runs on an internal clock. This clock is coupled to the sync pulses. That is the sync pulses of the previous SSTV-line, or even better a fly wheel frequency derived from several previous sync pulses.
This process calculates the current position in the frame memory and stores there the latest demodulated grey value number, given by process 1.

And then there is a third process:
3. A crystal stable clock calculates the addresses from where a grey value is read, converted to analogue and transferred to your 625 line monitor.

I don't know if you need absolutely three microcontrollers to perform these three processes, or that you can combine two processes in one uC. I can imagine that the processes 1 and 2 can be combined in one uC, as process 1 runs on a external event (the zero crossings) with the aid of an internal timer, while process 2 will run on the interrupt of a second internal timer. And both processes are relatively slow, while process 3 is much faster.

Does this help? Good luck.!
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Sat Nov 23, 2019 1:24 pm

Klaas Robers wrote:Steve, your problem is: time. Good luck.!

Absolutely agree! The use of the word 'decouple' in reference to time is perfect, 'uncouple' would also work.

Don't worry Mr. Einstein or Mr. Hawking, we're not going to step on your toes!

In the MkI version the decoupling of time was done by producing an analogue (continuous-time) signal, then re-sampling to produce a discrete time-sampled signal. Here it is desirable to side-step that process.

I need some more time to ruminate on this...

Steve A.

Who has read "A Brief History of Time, Stephen Hawking"? I have, about six times...do I understand it?...not sure!
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Klaas Robers » Sat Nov 23, 2019 6:58 pm

Indeed Steve. The analogue FM-demodulator had no discretisation (sampling) of the time. Theoretically you should up-sample the demodulated video signal, so calculate extra samples in between. But that is very difficult, because the sampling process is floating in time, following the frequency of the FM input signal. But for a video type of signal quite some distortion is allowed, because we will not SEE it afterwards. I guess that "sample and hold" is good enough, and that is what happens when you demodulate zero crossing for zero crossing and always use the latest sample.

A way to go would be:
- Build the software FM-demodulation in a PIC,
- do D-A conversion, then you have an analogue video signal back,
- feed that into the MK I version, in stead of the analogue signal
- (I would feed it in my fully analogue monitor)
- and look at the result.

- Then do the next step in a fixed sample rate.
- In the mean time you get used to what you were doing
- and may think about merging the two processes in one PIC.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Sun Nov 24, 2019 10:29 am

Klaas, I guess you could break down the objectives into two major chunks:-

1) Improve/replace the Robot 70 SSTV-analogue demodulator, to an extent I would like to think the 'improvement' phase has been achieved...however there's more that can be done here...which is the 'replace' stage.

2) Reduce the complexity of the MkI up-converter...currently work in progress...

If as you mention you have a P7 SSTV monitor you'd possibly be only interested in the first item. I've got a few P7 CRT's here, one day I'll get around to using them!

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Harry Dalek » Sun Nov 24, 2019 4:20 pm

Steve Anderson wrote:Klaas, I guess you could break down the objectives into two major chunks:-

1) Improve/replace the Robot 70 SSTV-analogue demodulator, to an extent I would like to think the 'improvement' phase has been achieved...however there's more that can be done here...which is the 'replace' stage.

2) Reduce the complexity of the MkI up-converter...currently work in progress...

If as you mention you have a P7 SSTV monitor you'd possibly be only interested in the first item. I've got a few P7 CRT's here, one day I'll get around to using them!

Steve A.


One good thing about Analog days were you tended to make the same thing with less parts so it was less complex, looking at stages you could work out how it worked or replace the stage with a new idea ,reading how its going i can see how how complex it is to improve the analog way with things digitally .

But what you are doing there is no other way unless you want to solder a room full of transistors together !

I am viewing Steve just don't have the knowledge on this subject to contribute but hope you keep on going with it ,it keeps these systems alive and hobby the going .

I was trying my deep image P7 SSTV the other day and i found the external plug in power supply we made originally for the Anderson monitor which i also use for this ,the torriod transformer had shorted inside it and was heating up ....i replaced it with a normal transformer perhaps 2 amps the sstv works but the adjustments are all off on the deflection and modulation so i need a bigger transformer ...any case what i am getting at here is the 70 year old HV transformer is still going strong while the 1990s low voltage Torriod is dead just shows you . :roll:
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: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Mon Nov 25, 2019 3:24 pm

Harry Dalek wrote:...any case what i am getting at here is the 70 year old HV transformer is still going strong while the 1990s low voltage Torriod is dead just shows you . :roll:

Yep, no surprise there!

When I do get around to a P7 CRT SSTV monitor I'll probably use a bit of each technology, say the demodulator as mentioned here and valves/tubes for deflection and cathode/grid drive. A hybrid using bits where best suited, I'm not aiming for something that can be put in your pocket or run off batteries! (Well maybe a car battery, I do have a 300W/240V inverter in the car...).

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Harry Dalek » Mon Nov 25, 2019 5:09 pm

Steve Anderson wrote:
Harry Dalek wrote:...any case what i am getting at here is the 70 year old HV transformer is still going strong while the 1990s low voltage Torriod is dead just shows you . :roll:

Yep, no surprise there!

When I do get around to a P7 CRT SSTV monitor I'll probably use a bit of each technology, say the demodulator as mentioned here and valves/tubes for deflection and cathode/grid drive. A hybrid using bits where best suited, I'm not aiming for something that can be put in your pocket or run off batteries! (Well maybe a car battery, I do have a 300W/240V inverter in the car...).

Steve A.


Some times its good to have a analog monitor to test against the software monitor, in my case when you want it my Torriod go's bung :roll:

Yes no need for a portable one but it is nice to have one !

I hope you do make one, be interested to see it come together and your demodulator is in mine...just remade it for the record lathe.
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: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Mon Nov 25, 2019 5:24 pm

Harry Dalek wrote:I hope you do make one, be interested to see it come together and your demodulator is in mine...just remade it for the record lathe.

Er...why Harry? Unless you mean for playback. I venture to say that you'll get nowhere trying to record the baseband (demodulated) signal. Record the SSTV sub-carrier, that's OK...the 1200-2300Hz signal.

Although the revised Robot 70 demodulator isn't perfect, it actually does quite a good job. Yes, it could be better, especially 'that' output filter - but I take responsibility for that, it wasn't part of Robot's original design. A large part of the reason I'm working on a replacement currently.

I did buy the 3" and 5" CRTs some years ago specifically for NBTV and SSTV use. They've been sat on my shelves all that time...time to pull my finger out...

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Harry Dalek » Tue Nov 26, 2019 8:42 pm

"Steve Anderson


Er...why Harry? Unless you mean for playback. I venture to say that you'll get nowhere trying to record the baseband (demodulated) signal. Record the SSTV sub-carrier, that's OK...the 1200-2300Hz signal.


Yes for Playback

I want to use the line sync pulse to control my geared motor which is controlled via PWM at the moment to the wanted 78 RPM speed but there is drift ..
I was thinking as in NBTV we use the videos sync to control the motors mechanical sync to the correct speed and so frequency ...Here i am using a clock 16 hz and the 16hz mechanical sync is from the records Slow scan video ( which is drifting below and above 16hz at the moment) ....i needed the demodulator to get the line sync pulse from the baseband ..which i have via klass's line sync circuit also ...i suppose there are simpler circuits to do all this but i knew yours and klass's circuit would work so why not use it again .
I suppose its more like a mechanical camera where you need a clock and mechanical feed back .

It did cross my mind to record the base band ! sounds like its a bad idea ! i have to be selective as recording can only be done once i have a box of dud cds dvds from trial and error .


Although the revised Robot 70 demodulator isn't perfect, it actually does quite a good job. Yes, it could be better, especially 'that' output filter - but I take responsibility for that, it wasn't part of Robot's original design. A large part of the reason I'm working on a replacement currently.


It works well enough for every thing i have tried ....its so good knowing something will work if build to the design

I did buy the 3" and 5" CRTs some years ago specifically for NBTV and SSTV use. They've been sat on my shelves all that time...time to pull my finger out...

Steve A.


Yes you must use them ! and you can use them well which would be a shame if they never got built in one of your projects ,i still have many thanks to Andrew which i will use for my future projects ,the Binocular was the first for the those ....
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed Nov 27, 2019 4:12 pm

Harry Dalek wrote:It did cross my mind to record the base band ! sounds like its a bad idea !

Just like NBTV the problem becomes one of LF response - except far worse! ...In the milli-Hertz range, that's the reason why SSTV is modulated onto a sub-carrier.

When it comes to extracting syncs here's my understanding of the standards involved for the EU format, either 120 or 128 lines. The US variety will simply have a slightly longer line-time of 66.7ms.

Steve A.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed Nov 27, 2019 5:31 pm

I might add, what I've posted above isn't set in stone, but it's what I try and aim for. Remembering the line rates were generally derived from the power mains of 50 or 60Hz, so in those days the tolerance may have been greater than now. (EU 50Hz/3 = 16.7Hz or 60ms/line, US 60Hz/4 = 15Hz or 66.7ms/line).

A good design would accept a few percent either way of the selected standard.

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Harry Dalek » Wed Nov 27, 2019 5:54 pm

Steve Anderson wrote:


Just like NBTV the problem becomes one of LF response - except far worse! ...In the milli-Hertz range, that's the reason why SSTV is modulated onto a sub-carrier.


I read in the old news letters those trying to record NBTV on cassette's those that wanted better results than as is ... was AM modulate NBTV video on a high KHZ carrier 10 khz tried means ,i think they have also tried FM but doesn't that make the bandwidth wider ?

I would like to Try NBTV on the record recorder but at the moment SSTV is hard enough to get right if i do i will move on..

When it comes to extracting syncs here's my understanding of the standards involved for the EU format, either 120 or 128 lines. The US variety will simply have a slightly longer line-time of 66.7ms.

Steve A.

[/quote]

Most of the software players TX are American standard so have just been working with that on my recordings ,main problem with the syncs are with no feed back to control the motor they are as you saw swinging either side of the line frequency ,if it behaves and using the the sync pulse recorded to control the motor it might line up those raster lines nicer ..when i have time to sit down and connect the feed back we will see :roll: ...
Its funny as i am trying the most primitive way to record SSTV and you are using the most sophisticated way to convert it either way just shows there is still an interest at least that visit here .
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: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed Nov 27, 2019 8:39 pm

Well, there's no reason a system cannot be made dual standard for US/EU rates, it's actually quite simple...so why not? Some are lazy and ignore the rest of the world...I wonder who?

Today the recording and playback of NBTV is quite easy - down to DC frequencies - actually DC isn't a frequency at all...I digress..

A simple sound-card (or its modern equivalent) will do the job. If it can sample at 48kHz or 96kHz you're in business! If you wish to include sound then you have a few decisions to make...but for SSTV 8kHz sampling is enough, which in the audio world is viewed as telephone quality. No great demands made on the hardware, and most RS232 interfaces should be able to handle it where needed.

If you consider the SSTV bandwidth being 1kHz and the NBTV bandwidth being 10kHz, there's no reason why a subcarrier-based NBTV system of 12-23khz shouldn't work fine. No good for phone-lines or HF comms, but it is a possibility, though I'm NOT suggesting it as a standard...there are enough already!

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Harry Dalek » Thu Nov 28, 2019 5:00 pm

Steve Anderson wrote:Well, there's no reason a system cannot be made dual standard for US/EU rates, it's actually quite simple...so why not? Some are lazy and ignore the rest of the world...I wonder who?


People who speak with r's in every word ? who could they be who knows :wink:
Well i agree rather use our mains frequency standard divided to our SSTV standard line frequency ..but software is lacking i think i still have one DOS program that does both 8 and and 7 sec only one i have ever seen must of been posted up some where .
Any case it reason i use the 8 sec only because i can test my recordings ...

Today the recording and playback of NBTV is quite easy - down to DC frequencies - actually DC isn't a frequency at all...I digress..


Well AF can be RF with an antenna so isn't any wave made electrically RF only via a Gas liquid or solid AF ..

A simple sound-card (or its modern equivalent) will do the job. If it can sample at 48kHz or 96kHz you're in business! If you wish to include sound then you have a few decisions to make...but for SSTV 8kHz sampling is enough, which in the audio world is viewed as telephone quality. No great demands made on the hardware, and most RS232 interfaces should be able to handle it where needed.


IN my case it has to be a correct speed 33rpm to low i can not emboss the frequencies they are lost jammed together 45 to 78 rpm it works faster the RPM the better so long as i can still keep the play back head on the tracks and not fly off !.

If you consider the SSTV bandwidth being 1kHz and the NBTV bandwidth being 10kHz, there's no reason why a subcarrier-based NBTV system of 12-23khz shouldn't work fine. No good for phone-lines or HF comms, but it is a possibility, though I'm NOT suggesting it as a standard...there are enough already!

Steve A.


Yes i think once i get around to NBTV i will modulate it on a carrier ...if it means it works why not use it if it works for cassette tape should work on a record at the moment i think my magnetic head can do 8 or 9 khz but thats it ...i have another idea to try when i get around to it fix the bandwidth problem .
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: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Sat Dec 07, 2019 5:00 pm

Harry Dalek wrote: Well i agree rather use our mains frequency standard divided to our SSTV standard line frequency ..but software is lacking i think i still have one DOS program that does both 8 and and 7 sec only one i have ever seen must of been posted up some where .
Any case it reason i use the 8 sec only because i can test my recordings ...

In the Mki SSTV-625 up-converter and also the current MkIII (there never was a MkII) I plan for it to be able to handle 120 or 128 lines, either derived from 60Hz mains or 50Hz - in all four combinations...though they're usually derived from a crystal source these days.

The output will be 625/50 unless there's a demand for 525/60. But most domestic TVs or monitors made in the last 20 years or more are multi-standard and they can almost handle anything thrown at them - a lot including SECAM, not that colour matters here. Even a 405 version could be done but I imagine there would be little, if any, demand for it.

Anyway, must get back to the task at hand...

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