NBTV/SSTV-625 Up Converter MkIV

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 MkIV

Postby Klaas Robers » Thu Jan 28, 2021 7:27 pm

Chris,
the picture above is generated with the aid of a pixel editor (e.g. Paint). But that is not what you want to know.

Then the file is programmed into an EPROM, which fits into my SSTV-monitor in Heathkit SB-style. This is part of the built in SSTV picture generator and can be outputted via the audio FM generator. This gives the SSTV sound signal, that I recorded on my laptop. In this way I came to the .wav files.

There are more SSTV pictures stored in the same EPROM, which I can choose by rotary switches on the front (bottom left and middle).

SB-500-testbeeld3.jpg
SB-500-testbeeld3.jpg (103.77 KiB) Viewed 7264 times

The testpicture is editted onto the "screen", it is too difficult for me to make a photograph off the P7 screen. You can see it clearly, because the monitor is in the "off" position, there is no light in the red pilot lamp and no light in the sync-LED.
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Re: NBTV/SSTV-625 Up Converter MkIV

Postby Steve Anderson » Thu Jan 28, 2021 8:07 pm

Harry Dalek wrote:Arrrr So software that can make a 8 sec with a VIS code will cause problems mmm,an idea could be to edit the VIS code out with a sound editor ?
That might seem an obvious option, but it'll mess the timing up. If there is VIS code this either needs to ignore it, or use it to some degree...well it has to, there's no frame sync otherwise with VIS code. The code IS the frame sync.
Harry Dalek wrote:Am i right in saying the standard 7 and 8 sec SSTV started with a frame pulse so this could still be a problem unless you manually reset which more than likely you have built in here.
I could add a manual 'frame reset' button as per the old CRT versions, the read processor still has quite a few I/O pins free, I've not thought of it before as the MkI was so reliable in this regard. But under poor signal conditions, who knows. It's a push-button and one resistor to add...though again I need to think on this.

Steve A.

Had a bit of a fall yesterday, I'm OK, just somewhat sore. So I can't perch on my workshop 'bar stool' (I guess correctly termed a laboratory stool) to wield the soldering iron as I had intended to. I need some back support now.

To quote Phil Collins at the opening of a recent performance, "Getting old sucks!"

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

Postby Harry Dalek » Thu Jan 28, 2021 9:07 pm

Steve Anderson wrote:I could add a manual 'frame reset' button as per the old CRT versions, the read processor still has quite a few I/O pins free, I've not thought of it before as the MkI was so reliable in this regard. But under poor signal conditions, who knows. It's a push-button and one resistor to add...though again I need to think on this.
Steve A.


Just an idea sounds like it might be possible from your thoughts same thing as a single push button switch on an old monitor .perhaps just stick with how it is and see how it go's sounds like it could be added later if need be .

Had a bit of a fall yesterday, I'm OK, just somewhat sore. So I can't perch on my workshop 'bar stool' (I guess correctly termed a laboratory stool) to wield the soldering iron as I had intended to. I need some back support now.

To quote Phil Collins at the opening of a recent performance, "Getting old sucks!"

Steve A.


Nothing worse had 2 falls like that ,the first thought i was a goner could not even sleep due to the back pain , second was of late fell out of the Green Bin as you do ! ...may be getting old is a good thing stops you climbing on things !
Take it easy Steve its a life lesson just don't get hurt next time you do it again :wink:
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NBTV/SSTV-625 Up Converter MkIV

Postby acl » Thu Jan 28, 2021 9:36 pm

Steve,

Sorry to hear about your fall , all the best for a timely recovery.

Chris
Last edited by acl on Thu Jan 28, 2021 9:50 pm, edited 1 time in total.
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NBTV/SSTV-625 Up Converter MkIV

Postby acl » Thu Jan 28, 2021 9:38 pm

Klaas,

Would it be possible for you to post details of your SSTV generator as it may help setting up Steves convertor.

Regards Chris Lewis
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NBTV/SSTV-625 Up Converter MkIV

Postby acl » Thu Jan 28, 2021 10:08 pm

001.JPG
How we did it in the old days. Unfortunatly unable to get EPROM information
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NBTV/SSTV-625 Up Converter MkIV

Postby acl » Thu Jan 28, 2021 10:13 pm

002.JPG
Dedicated device to store characters.
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Re: NBTV/SSTV-625 Up Converter MkIV

Postby Klaas Robers » Fri Jan 29, 2021 7:52 am

Steve, to skip the VIS-code.... Can you not at the detection of a longer 1200 tone, clamp the write addressing to the centre op line 0, and release it when the tone stops? That will work on the V-sync as well as the VIS stop bit. Then the stop bit will act as a V-sync.

I know that it is difficult to discriminate between the 1200 Hz and the 1100 and/or 1300 Hz in the VIS-code. For the H-sync (5 ms) the bandwidth of the sync tone detection should not be too narrow. But for a longer (30 msec) tone it could be done.

I experienced with the "Heathkit"-monitor, which has a switcheable LC resonator, 1000 - 1100 - 1200 - 1300 - 1400 Hz, that it in most occasions runs too at the 1100 Hz or 1300 Hz setting.

Good luck!
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Re: NBTV/SSTV-625 Up Converter MkIV

Postby Klaas Robers » Fri Jan 29, 2021 7:58 am

Dear Chris,

I know that Steve has a well working SSTV generator, so there is no need for my genrator. On the other hand, I guess that the circuit diagrams of my generator are already somewhere in this forum. I did quite some fine tuning of it with Steve in the past. My tones were all too low. In the mean time that is corrected. Ask Harry where to find it, he knows to find everything in this forum.
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Re: NBTV/SSTV-625 Up Converter MkIV

Postby Steve Anderson » Fri Jan 29, 2021 12:59 pm

A thought...the actual VIS code that determines the mode is comprised of only 1100 and 1300Hz tones, this is the only place those frequencies appear, the actual image shouldn't contain them at all. Once either of these two are reliably detected all we do is wait for the 'stop tone' at the end at 1200Hz which effectively marks the beginning of the video data proper.

These are all 30ms long and should be fairly easy to differentiate the 1100 & 1300Hz from the 1200Hz, the simplest method being a counter. e.g. 30ms of 1100Hz = 33cycles, 30ms of 1300Hz = 39cycles, and of course 30ms of 1200Hz = 36. What maybe worthwhile is frequency doubling those (e.g. a full-wave rectifier or counting zero-crossings) to obtain 66, 72 or 78 counts. So allowing for a bit of SSB mis-tuning 1100Hz = 64 to 68 counts, 1200Hz = 70 to 74 counts, and 1300Hz = 76 to 80 counts.

That's one possible method, other suggestions welcomed. Tuned filters may become a bit 'messy' but are possible.

Another possibility is using LM/NE567 tone decoder chips, they've been around forever but not cheap as I recall. However this adds more hardware...the whole idea was to simplify the MkI after all...

Steve A.

If anyone knows of a published article for VIS decoding, that may be a source of ideas, either hardware or software based.

Note:- I have no intention of using VIS codes, all I'm doing is making this device VIS-tolerant. It'll use the VIS as a 'pseudo'/replacement frame pulse and that's all. As if my 'in-box' or 'to do list' doesn't have enough stuff already!
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Re: NBTV/SSTV-625 Up Converter MkIV

Postby Harry Dalek » Fri Jan 29, 2021 3:27 pm

Oh don't worry to much Steve improvements can become endless converting a standard original Cop SSTV to 625 line is more than enough ,i would leave it for another version if it.
I have finished the main board part almost,... i think ...apart from adding resistors for the red green and blue freeze sync and clip indicator ,i am thinking of using a tri colour led might have to adjust the resistor values for this or brightness as levels will be different i think knowing that 3 colour led i have .

Another question or 2 do i need sw1 and 2 since i think it is for programming ?

Just have to connect 1F and 1E connections and i can move onto the panel controls .
Attachments
P1070636.JPG
P1070634.JPG
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 MkIV

Postby Steve Anderson » Fri Jan 29, 2021 3:47 pm

Klaas Robers wrote:I know that Steve has a well working SSTV generator...

Well, yes, and thanks. But the preparation of the source jpg (or whatever) was quite labour intensive requiring a lot of effort per picture. But once done, that's it. You slowly build up a library of subject matter.

But as a follow-on to this I'll have a go at a still to SSTV convertor. How to do this and how to produce a slide-show as a result I still have to consider.

Of course a FSTV to SSTV converter is possible, but the results are are often poor depending on the FSTV camera resolution/contrast and other factors, often resulting in poor resolution and smearing, not too dissimilar to the Apollo 11 video downlinks (don't get me wrong, amazing for the time, the distance, and what they had to work with). Even so, after half a century I'm rather hesitant in going down that route.

If the still photo is a good one there's no reason why it won't work in SSTV, whereas a frame-grab in FSTV is somewhat hit-and-miss. Plus there's no high-speed (a relative term) frame grab required, often resulting in the artifacts mentioned before.

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

Postby Steve Anderson » Fri Jan 29, 2021 6:16 pm

What am I thinking?...I'm getting too close to this project perhaps...we've now got some 300ms of VIS code that is below 1500Hz, which we would normally think of being V sync...here it is! So a simple 'below 1400Hz or 1350Hz detector' will do the job, with a suitable duration...

30 1200 VIS start bit
30 bit 0 1100hz = “1”, 1300hz = “0”
30 bit 1 “”
30 bit 2 “”
30 bit 3 “”
30 bit 4 “”
30 bit 5 “”
30 bit 6 “”
30 PARITY Even=1300hz, Odd=1100hz
30 1200 VIS stop bit

Duh! A Homer Simpson moment!

simpsons_homer_doh-928x523.jpg


Steve A.

I wonder if the original designers of the VIS code had thought of that, all kudos to them if they had!

Maybe I should take a break and sit on a beach for a week...sorely tempted...only a 90-minute drive away, then a quick ferry...it's a very pleasant 35 degrees now...Celcius of course...
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Re: NBTV/SSTV-625 Up Converter MkIV

Postby Harry Dalek » Fri Jan 29, 2021 8:45 pm

Klaas Robers wrote:Dear Chris,

Ask Harry where to find it, he knows to find everything in this forum.


Not this time ...it is mentioned a few times in a few posts back to 2015 but mainly chatting you have a built in picture generator in your monitor but no schematics Klaas .

Steve Vertical Interval Signaling Codes are mentioned here
http://www.g0hwc.com/sstv_modes.html
Last edited by Harry Dalek on Fri Jan 29, 2021 10:01 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: NBTV/SSTV-625 Up Converter MkIV

Postby Steve Anderson » Fri Jan 29, 2021 8:50 pm

Done, I'm off tomorrow morning, I'll take the solar charger for the laptop with me, use the mobile phone as a wi-fi hotspot, and zonk out. There's no electricity on the island, at least the part I'm going to. I'll stay in contact, sporadically...back here on the 7th...

Steve A.
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