Vintage SSTV transmit converter

Forum for discussion of SSTV topics. Slow Scan television (SSTV) is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or colour.

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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Sat May 04, 2024 1:08 pm

Hi Chris, interesting. Something I've been meaning to get to grips with for a long time is PCB layout/creation, just haven't got around to it. I've tried one or two software packages, but they're so convoluted and complex I give up easily. I've tried KiCad, Eagle and one or two others, none seem to 'stick' with me. Maybe I should make a more determined effort?

However if you're so inclined perhaps you might want to have a go at something I've created, either in the past or that's up-coming. The TIFF-SSTV thing isn't going to be too busy, it'll use standard through-hole components (no SMD), and it should all fit on a single 100x160mm Eurocard with a single DIN41612 64-pin connector, though 32-pin versions are available. If the DIN41612 connector isn't wanted, wiring direct into the PCB holes provided for it is an alternative. Though additional alternative connectors could be provided for, maybe a 25-pin D-type?

A good 'example' project might be my MkI SSTV-to-625 up-convertor, though I'm not seriously suggesting it. The prototype was built on two Veroboards/Stripboards, one 120x80mm, the other 92x54mm, for a total of 146sq.cm. The Eurocard mentioned has an area of 160sq.cm., so it should be a comfortable fit, even with the DIN connector.

My initial thought is, "What about Ground-planes?" One side of the board (usually the top/component side) being a large area of copper at ground/earth/0V with just the occasional track where signals/power rails/etc. have to cross on the other side. Extra 'goodies' like PTH (Plated Through Holes) appear to be close to, or at, zero additional cost.

PCBWay seem to be 'Flavour of the month' at the moment....though there are quite a few others....

Steve A.

DIN41612 Example.jpg
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Re: Vintage SSTV transmit converter

Postby acl » Sun May 05, 2024 2:06 am

Hi Steve,

Ralph Taggart and myself use ExpressPCB plus, a free piece of software and I use 100% of it's capability. The only downside is you pay for the PCBs from them and get the Gerber files back. The only problem is they use UPS delivery which costs more than the boards then customs pile there charges on. The software is brilliant and intuitive. You don't have to draw the circuit up in etch a sketch you can just dive in. When you are about to place an order the design is scrutinised on your PC to check clearances missing pads etc. Technical support is second to non. Although in the States I emailed them with a query with the earthed plane on Johns SSTV converter and within 20 minutes someone had corrected my design and sent my design back no charge. (If you don't do it right all tracks are shorted). Lets see how you get on with the TIFF to SSTV converter design.

Regards Chris
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Sun May 05, 2024 12:39 pm

OK, I don't think I tried ExpressPCB plus in the past, I'll give it a go. The TIFF-to-SSTV device should be at a stage where the prototype build could commence by the end of the coming week. I'll probably have to order some components, so that may slow things down. Then there's the delight(?) of creating the code.

Because of the development of semi's (particularly memory) it will probably be a 3.3V system, but it's really no different to the familiar 5V.

Steve A.

What is rather frustrating is that I know somewhere I have 12 128k x 8-bit (1Mb) serial RAM chips, somewhere! I can't get them locally, which means ordering from the UK (probably). The alternative is turning this office/workshop upside-down and giving it a good shaking. In this heat at the moment, 43C, I'm in no mood to do that! No, I don't have air-con in this room...which worries me for the PC. They're usually specified to just 40C.

For those in the US...
40C=104F, 43C=109.4F
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Mon May 06, 2024 2:05 pm

For the moment I'll assume that I can get the 1Mb (128kB) serial RAM chips, or find those I know i have somewhere. But I'm in the UK at the end of this month, May, for a week or so, so I may have a chance to get some then. I can get 256kb (32kB) versions here which would just work if need be. I can order from the UK, but it's a hassle...

It would be quite easy to make the hardware and software work with either, so it's no big deal, just move a jumper to tell the processor which version of RAM is installed. Though the processor can interrogate the RAM at start up and ask the question, "How big are you?"

Likewise with the micro, I'd prefer to use a version again that isn't souced locally, but easy in the UK. A 20-pin DIL/DIP packaged PIC18F14K22.

At this stage I should point out that a USB-UART device will be required. FTDI do a number of adaptor 'cables' which aren't that cheap, but they do work. There are many similar devices, much cheaper, on the 'net, but I've not used them. Of course they can be used with many other home-built devices and projects, i.e. they are useful!

Or simply add a USB-RS232 device (dongle) to the PC if it doesn't have a RS232 port. With the addition of a MAX3232 (not MAX232) to the TIFF-to-SSTV unit, it should work fine. Even RS232 speeds are adequate for this. The MAX3232 is for 3.3V supplies used here (actually 3.3 to 5v), the MAX232 is only for 5V. Otherwise they are very similar.

The FTDI cables/devices also include the 'handshaking' lines for where used (not in this) and can also provide power (5V or 3.3V at about 250mA depending on version)

https://ftdichip.com/product-category/products/cables/

I have no connection to FTDI....blah, blah...

Steve A.
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Thu May 09, 2024 6:42 pm

For both the upcoming TIFF-to-SSTV and the SSTV-to-625 units I intend to use serial RAM rather than the usual parallel variety. It cuts down significantly on wiring and board area.

Instead of more than a dozen address lines (pins), plus eight for the data I/O and a few more for writing, chip select and so on, all that's needed is eight pins including power.

For a 128kB (128 kilo-Byte) RAM all that's required is two 8-pin DIL chips, not a single 28 or 32. Whatever controls the read from, and writes to the RAM, only requires 10 I/O pins.

SSTV v7 Up Converter 1-Model.gif
SSTV v7 Up Converter 1-Model.gif (41.74 KiB) Viewed 2822 times


It is true that serial RAM isn't as fast as parallel, but here it's fast enough, or should be!..if I understand the datasheets correctly...

The ports shown RCx, RBx could be any suitable port on the micro...the mode of RAM operation is SQI, Serial Quad Interface.

Steve A.

I'm not sure why the sketch is so large...again, I had this problem a few years ago, can't recall how I fixed it...
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Thu May 09, 2024 7:02 pm

Once I've made sure that the timing is OK for the SSTV-to-625 device I'll start a new thread for it, and also when I get to the TIFF-to-SSTV unit. The TIFF-to-SSTV unit will probably only require one 8-pin serial RAM chip...the timing is also much relaxed...

I need the SSTV-to-625 unit first as the MkI version has vanished!! I probably still have it somewhere, just buried...

Then will come the TIFF-to-SSTV build.

BTW, I have again improved the SSTV demodulator, I hope gone is the ringing after large/fast amplitude transitions as well as improved dual full-wave signal rectification. As with anything analogue it is a bit more complex, but not excessively so. Just three 14-pin chips in total, but quite a few passives...it is analogue after all!

I may have to look at the modulator too, I'm not too cetain of its filter integrity either...any error or mistake will be mine...

For all the above I still have PCB design in the back of my mind...but let's get the prototypes done first...

BTW, I do not claim originality for any 'improvements' I may have made. Most are copies, adaptions and/or modifications of others ideas or designs. Maybe one day I'll do something original!!

Steve A.
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Fri May 10, 2024 5:22 pm

I've just re-examined my DDS SSTV modulator and gave it a clean bill of health, the filter is fine.

Not so my modified Robot 70 demodulator where I replaced a significant portion of the final filtering (what little there was). In my opinion my supposed 'update' was sub-standard, entirely my fault, I hope I've corrected that now. That correction and other improvements will come soon. This time I want to be sure! Aside from the overshoot mentioned, it wasn't/isn't that bad.

Update once the revised version is built and properly tested.

I should have a good look at John Magliacane's version first, why re-invent the wheel?

Filtering artifacts in video are usually much more noticable than in audio unless really excessive. With distortion it's the other way around generally. Video Gamma correction is a form of pre-distortion to 'undo' the amplitude (brightness) non-linearity of a CRT, it does have other visible noise-suppression attributes too.

Steve A.
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Vintage SSTV transmit converter

Postby acl » Mon May 13, 2024 2:03 am

Hi there all,

Just doing some experimenting with my SSTV transmit converter. I have tried it with MSSTV and, although I did get it to scan the resulting picture was way off skew and couldn't be recognised. I know Harry tried this and got multiple frames on the page. I then tried QSSTV a Linux based program without any success. I assume both of these programs failed to give results due to the frame ident missing from the converter. Johns converter works a treat with my converter every time and will receive pictures from MSSTV . I will do a little more digging to see if any other programs exist even in DOS.

Harry , the offer for those LS chips for free is still on and we can compare waveforms between units to check both are working correctly.

Regards Chris
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Re: Vintage SSTV transmit converter

Postby Klaas Robers » Thu May 16, 2024 7:32 pm

Hi Chris,

I remember a waveform that you posted a few weeks ago and there it struck me that in the vertical sync pulse the H-sync was disrupted. It should be such that in fact the H-sync continues, but in the first line of a field the H-sync is stretched, so made longer to half that line, obscuring the video information of the first half of that line. In your oscillogram I observed a V-sync that inserted a half line of time, so there is a huge hick-up in the H-sync. If the monitor (program) assumes that the H-sync continues, and most monitors do so, then it will disturb the next (so all) pictures in order to restore the H-sync.

Good luck in curing this problem.

Klaas, PA0KLS
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Vintage SSTV transmit converter

Postby acl » Thu May 16, 2024 7:47 pm

Thanks for your input Klaas,

I have had fun building and testing the converter. I believe it has limitations for it's simplicity and it produces a perfect picture on Johns converter but I am experiencing trouble with the PC based programs. MMSSTV tells me I am off frequency yet Johns converter which is 'crack on' and has enough filters to ensure this works perfectly. I can transmit pictures from the PC to Johns converter and these are perfect. I haven't the technical expertise to start investigating any timing problems with the CCIR synch signals which may be associated with the original design so I think I will be satisfied as is.

Kindest regards Chris
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Mon May 20, 2024 5:53 pm

Hi Chris, as you know I'm off the the UK tomorrow for about two weeks. When I return from that trip I'll have a go at a newer version of my MKI SSTV-to-625 up-converter. I've already made a start, but with this trip coming up and other things I haven't been able to spend as much time on it as I would like. I'm already up to Mk5, perhaps this revised version will become the 'Real MkII'?

But it should be somewhat simpler in the digital domain, though the analogue sections are unlikely to change much. Though some improvements may well be incorporated. Time will tell.

While I'm in the UK I will log-in here as and when I can...
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Mon May 20, 2024 6:27 pm

However, in my rushed confusion r.e. my UK trip, I've got a little confused...this is really about 625-to-SSTV which is quite different. I don't intend on making one of these as I feel the source material is sub-standard. It's far better to convert a reasonable resolution JPG/BMP/TIFF to SSTV. The monochrome TIFF file format being the easiest, remove the 'header' and you're almost done...it's uncompressed and almost exactly what's needed...

File size shouldn't be an issue these days, they're under 100kB, almost nothing. An 8-second SSTV frame will still be 8-seconds. Though 8 seconds may sound a long time, I find it's not...when it comes to the more recent modes in colour and hi-res, that take minutes to recieve, that's too long for me, but there are many who appreciate that format...

Steve A.
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Thu Jun 06, 2024 8:10 pm

I'm back from my UK trip, simply gotta get my head around what I was doing and where I had got to...my mind is a blank right now....and only two weeks or so away...

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