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 acl » Tue Jan 14, 2020 10:47 pm

Thanks for clearing up these technical questions.

Regards Chris Lewis
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby M3DVQ » Tue Jan 14, 2020 11:41 pm

You can still use "modern" sstv programs, you just want to turn off automatic everything.
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NBTV/SSTV-625 Up Converter MkIII

Postby acl » Wed Jan 15, 2020 4:26 am

Sir,

I believe it was you who supplied me with software for the Raspberry PI which worked well although I still had trouble with Steve's files.

Kindest regards Chris Lewis
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NBTV/SSTV-625 Up Converter MkIII

Postby acl » Wed Jan 15, 2020 4:33 am

Steve ,

That makes sense , the original wouldn't need the VIS code as it was the only format available at that time. How would the MK3 handle eight second SSTV with VIS code included?


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My SSTV Encoder

Postby acl » Wed Jan 15, 2020 4:40 am

IMG_2610.JPG
My SSTV encoder prototype
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed Jan 15, 2020 1:41 pm

acl wrote:Steve, how would the MK3 handle eight second SSTV with VIS code included?

It should simply ignore it, it's a modified video line I believe, I'll look into it and make sure that's correct. Which means it may show up on the screen, much like VITC (Vertical Interval Time Code) used in analogue FSTV video recording and editing, though for FSTV it's in the overscan area at the top of the frame/field and shouldn't be visible normally. Same applies to the old teletext system.

If the VIS code is always on the same line it would be a simple task to blank that line...a big if!

Added later:- VIS code is nothing like a standard line, at least in duration, there's also now 16-bit VIS codes just to make things interesting!

There is a VIS code for the ROBOT 8-second mode, either 1, 2 or 3 - for Red, Green, Blue. The Green code is used for monochrome pictures. Same code(s) used for 8 or 7.2s modes.

I think I may have to take back what I said above, "It should simply ignore it..." I'll have to think on how to get it to handle signals with a VIS code, though not actually use it.

Also an updated modulator which can add (or not) the appropriate VIS code, then maybe some of these PC based software applications might spring into life?

Here's a listing of VIS codes, not sure how up-to-date it is, or how accurate, but note the ROBOT 8-second mode is described as 160 lines, 120 columns (pixels?). Also the Wraase 8-second B&W is 120x128, different, yet similar. Different codes too. (Wraase 8-second B&W, 17, 18 & 19) No mention of aspect ratios either.

Steve A.

I'm not going to spend too much time on this VIS matter at this stage, it may be an add-on later.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed Jan 15, 2020 6:59 pm

Chris, your SSTV encoder a posting back or so, is it operational? If so I'd be interested in receiving a a couple of files that it has generated to make sure I can demodulate/decode them...though at this stage I have no way to turn them into pictures/screen-shots, though in time I should be able to. Either post them here or use my e-mail please...

Steve A.

P.S. I have no idea what happened to the MkI up-converter, it's probably here somewhere....

P.P.S. I've found it, it wouldn't take that long to get it operational again, but I'll leave it until the MkIII is operational...though now I can't find the separate demodulator board...yep, I'll leave it until the MkIII version is up and running...
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Klaas Robers » Thu Jan 16, 2020 4:44 am

Two or three years ago, the last time that I attended the NBTVA-meeting, I had my SSTV-monitor with me and we (Chris and me) tried to display the built in 7.2 second pictures that my (Heathkit) monitor outputs. It did not work at all. I fear that the software in Chris' decoder expects a VIS code, and refused to start without a VIS-code. I can understand that, with the large number of deviating "standards" this is the first task that you do: Wait for and decode the VIS-code. If you are too young to realise, that there was a time without VIS-codes......

Yesterday I did a first repair on my Heathkit-monitor. Already quite some years the generation of the hardware sawtooth signal did sometimes work, other times it didn't. Then I just got a black picture (with sync, yes). It is difficult, as the signal is generated on a experimenters type PCB, which is not accessable when plugged in. The sawtooth signal is made in the four transistors (BC107 and BC177) in the right bottom of the PCB. The small electrolytic capacitor is the timing capacitor.

Foto print 1.jpg

The black plastic FCJ121 ICs are dual JK-flipflops in DTL logic. 6 volts supply voltage. This was what Philips (or was it Signetics?) produced in 1970. You see: wires on both sides, the holes were not plated through.

After quite some measuring with the oscilloscope on the output signals that were accessable on the connector, I concluded that an emitter resistor, of one of the BC107s, was not grounded.... Then, with the ohmmeter the bad soldering joint was truely found. Soldering iron.... and it works again.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Thu Jan 16, 2020 1:04 pm

Klaas Robers wrote:...If you are too young to realise, that there was a time without VIS-codes......

Unfortunately I don't fall into that category, I do remember the times when there were no VIS codes. The two people involved would agree to a standard beforehand and it all worked. Not that there was much of a choice of standards back then anyway.

I think, but I'm not sure, the attached item from 'Electronics Australia' in May 1974 may have started my interest in SSTV, I was 18 at that time...ho hum...

Today you'd use something like MPSA44 transistors (suitably biased etc.) instead of the 6BX6/EF80 tubes/valves, that saves nearly eight watts of heater power alone...and raise the anode/collector loads to perhaps 100k - it's not exactly a fast application!

Steve A.

Click each image for a better copy.

The European version of the 6BX6 is the EF80 - used by the millions in TV I.F. strips...

The voltage doubler at bottom right of the circuit diagram contains an error, don't copy it!
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sstv_2.png
sstv_3.png
sstv_4.png
sstv_5.png
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Klaas Robers » Thu Jan 16, 2020 10:13 pm

I do understand that an article like this (I have read it with great pleasure) will motivate an 18-year old boy to do something in SSTV. And of course I know the EF80 tubes. I don't know how many our Philips company has made. And I have still several of them. This was THE tube in TV if-amplifier stages. And I see in the photos more characteristic Philips components, e.g. the yellow-green foil capacitors. Good to see that our company was well known in Australia. And that the article mentioned Elcoma, our components division.

I looked into the definition of the VIS-codes, they are by far deviating from the SSTV video. And I did not find a VIS-code for 8/7.2 sec B&W video. The closest is a system with one complete 8/7.2 field for Red, followed by one for Green, having a different VIS code, and then one for Blue with again a different VIS-code. We see in this the development of a new system by different people where each new idea was finished and gave a new, different "standard". I didn't like it when it went into that direction and I still don't like that. It caused me that I left SSTV for what it was.
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NBTV/SSTV-625 Up Converter MkIII

Postby acl » Fri Jan 17, 2020 1:35 am

Steve,

If we can find a reliable courier that will deliver parcels to Thailand you can have the encoder for free. I built two so this one is superfluous to my needs. Also I have the demodulator I built and got working in a fashion with help from yourself . As it is now redundant as your excellent design uses software to decode the SSTV Signal.

Regards Chris Lewis
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NBTV/SSTV-625 Up Converter MkIII

Postby acl » Fri Jan 17, 2020 1:42 am

Link for construction of eight second monochrome SSTV generator using Arduido . Produces signals from small camera with option of callsign imposition.


http://k183.bake-neko.net/ji3bnb/page15.html

Regards Chris Lewis
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Fri Jan 17, 2020 2:04 pm

Klaas, yes, I remember Elcoma from my days in Australia, one, if not the component supplier in Australia at the time. The EF80 saw a lot of deployment in valve/tube radios that had FM, mono in those days, used also in the I.F. amplifiers though typically at 10.7MHz. I also have a few, I don't recall why I bought them.

I guess one of the things that attracted me to SSTV in the '70s was its simplicity, these days with VIS codes, colour and endless 'standards' it's all a bit daunting to the newcomer. As we'd say in English, "Shooting oneself in the foot." (A rather silly thing to do, usually unplanned, and hurts somewhat).

For monochome SSTV the VIS code is usually the Green channel of a certain standard, the Red and Blue are absent. Or the Y channel only in a colour-difference system.

It's a shame that there wasn't an all-overseeing body to maintain and issue these evolving 'standards', rather than the rather haphazard way they came about. Say the RSGB or the ARRL.

I agree with your sentiment, with the way SSTV evolved, I too lost some interest in it, it was/is a mess. That's why this has the header, "Cop McDonald's FM SSTV System."

Chris, thanks for your generous offer, I'll send you an e-mail shortly...

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

Postby Steve Anderson » Fri Jan 17, 2020 5:45 pm

Chris, the method I used to produce the SSTV files on this forum was as follows...

1, Choose subject photo, usually a JPG.
2. Convert to 8-bit monochrome.
3. Crop and resize to 256x256 pixels.
4. Save as a monochrome 8-bit TIFF file.
5. Strip off the header, just a few bytes.

You end up with a very basic 8-bit mono data package which is just what we need, I used Irfanview (a free download) to do it except item 5 where I used Hexedit (also free).

The modulator then processes that file ignoring every other line which means you end up with a 128x256 picture. The modulator cannot process reasonably 256 pixels in an active SSTV line, but it's no problem. But that was going through an analogue process which I wish to avoid this time...but a picture SSTV generator is next on the list of to-do items.

It may sound complex, but once you get the hang of it, it's quite easy and quick...

Steve A.

Original version follows....uses DDS (Direct Digital Synthesis) to do the job...unusually I didn't date the drawing, I would guess sometime in 2015...the code is just 91 bytes plus the sine look-up table of 256 bytes.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Sat Jan 18, 2020 7:12 pm

I eventually found the original DDS SSTV modulator, it needs a minor addition/change though...

I can't yet find the modified ROBOT 70 demodulator I built and used previously, it's here somewhere, but it shouldn't be required, though it would be nice to compare it with anything else...

Messy construction, but it is a prototype...

The T092 'transistor' in the upper right corner is a LP2950 +5V regulator for the micro, not shown on the circuit diagram.

Steve A.

My guess was almost right, photo files dated December 2014.
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