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 Harry Dalek » Tue Feb 13, 2024 5:05 pm

acl wrote:Well I have made a start Harry. I always find it is easier to build and test on a piece of plywood before committing to a case


OH great Chris ! one of us should get this going ! Power supply and video sync separator i see ,since i last replaced that last video transistor i have not had any problems i think it must of been leaving the brightness pot full turn in one position . Since it was not causing me any problems since haven't looked more into it .

Today when i came home from work i looked into whats happening after output of the 4066 and U17C opamp.

Screenshot 2024-02-13 161637.png


Below 2 videos are the 4066 sync control full left right positions scope readings taken at pins 2,3,9,10





Now whats happening after U17C Pin7 here adjusting the the White trimmer then the black trimer controls and its effect on the signals



Now this is where the good news ends today ! sort of i moved onto the 566 VCO adjusted the white and black trimmer controls to see the effect on the triangle wave the white control does seem to adjust the frequency a touch but i didn't noticed this when trying the Black trimmer control ...Now moving on to U17D wiring is correct and i am getting bugger all out of the opamp ! nothing or very very weak at pin 8 ...i am almost at the point of building just this opamp circuit and seeing if its giving the same result so close but yet so far !
Thinking out aloud below
R45 lowing the voltage signal to the 566 perhaps a trimmer might be better here ,and R48 on the input of U17D here is a voltage follower the voltage output is equal to the voltage input gain of 1 mmmm for me this is no good at the moment ! not much coming out the 10K to its input
Any ideas here ?
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DSCN9654_x264.mp4
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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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Vintage SSTV transmit converter

Postby acl » Wed Feb 14, 2024 6:12 am

Screenshot 2024-02-13 161637.png
Screenshot 2024-02-13 161637.png (341.84 KiB) Viewed 706 times


Harry,

I have checked the schematic against the PCB and everything appears correct. Check U17 pin 4 is at +12 volts and 11 at -12 Volts dc . Verify pin 5 U17c can be adjusted from zero to +2.1 Volts with VR5 (white). When voltage on pin 6 U17C rises above the threshold set by VR5. try with VR6( black) at max. If not 'lift R45 and see if it clears.
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Wed Feb 14, 2024 2:16 pm

..."Though first I need to find a source of 625 video!"
Quoting myself there. I did check yesterday and I have no source of 625 (or 525) video now. The only analogue source I now have is component HD 1024 with tri-level syncs from the set-top box, and I have no say in the image, only what is broadcast, no good.

So for me to generate SSTV it's going to have to be a image file as the source, jpg, gif or better, tiff. That's what I did to generate the SSTV files for the MkI SSTV-625 up-converter. The source image does require some simple preparation using some free software, e.g. Irfanview.

The original jpg (or whatever) is converted to monochrome, then cropped and re-sized to 256x256 whilst retaining the the correct vertical to horizontal ratio, then saved as a TIFF file. This is then sent to the external SSTV generator.

As I mentioned previously this could be done on a PC with dedicated software, someone has probably done so already, but there's no satisfaction to me in loading someone else's software and saying it's a 'done deal'. It could be said that using Irfanview is tantamount to the same thing.

Caught between a rock and a hard place...

Steve A,

I do have a few ideas that remove the PC entirely from the process, as per the project referred to here, but at the moment that's all they are, ideas...

I have been accused of 'hating PCs', (not on this forum, but elsewhere), not true. Why do others design and build amateur radio transmitters and receivers themselves when they could easily go out and buy them? Because they want to, they can, and therefore do.
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Thu Feb 15, 2024 8:28 am

Steve Anderson wrote:..."Though first I need to find a source of 625 video!" Quoting myself there. I did check yesterday and I have no source of 625 (or 525) video now. The only analogue source I now have is component HD 1024 with tri-level syncs from the set-top box, and I have no say in the image, only what is broadcast, no good.



I am pretty lucky i have many ways the system converter ,many cameras and vcrs Dvd players even some of my still cameras output to 625 lines .
might be an idea to track down a small something that does it at a flea market car boot sale second hand store ,if any thing good to have it for the hobby !~ an unless you can make a test card generator your self .

So for me to generate SSTV it's going to have to be a image file as the source, jpg, gif or better, tiff. That's what I did to generate the SSTV files for the MkI SSTV-625 up-converter. The source image does require some simple preparation using some free software, e.g. Irfanview.

The original jpg (or whatever) is converted to monochrome, then cropped and re-sized to 256x256 whilst retaining the the correct vertical to horizontal ratio, then saved as a TIFF file. This is then sent to the external SSTV generator.

As I mentioned previously this could be done on a PC with dedicated software, someone has probably done so already, but there's no satisfaction to me in loading someone else's software and saying it's a 'done deal'. It could be said that using Irfanview is tantamount to the same thing.

Caught between a rock and a hard place...

Steve A,


A lot of people live in the now and have no interest in the past even asking about this project the other day it was mentioned a few times i got we are doing it this way these days well true but i am not interested what they do these days i am interested in ( how it was done at that time for that reason that way ) i don't want to pack my soldering iron away .

It was more than likely the same circumstances for Radio every one that could would build them then you could buy a manufactured cheaper better nicer than what you could make and there went that idea unless for learning purpose's ...here it is the same a personal interest to learn how it was done it will not be of interest to most but only the few .

The photo to SSTV signal has been done fair few times for the PC if any thing a nice tool to test your monitor but doing it all via PC just because its better and you don't have to build any thing ( THINK ! ) is a problem ...all this will come to the point where you ask AI to any thing that can be done on a PC screen or what ever that screens ends up looking like and bingo no one knows how any thing in the future because they have no interest in the so called antiquated past i suppose we are the archaeologists of electronics here .

I do have a few ideas that remove the PC entirely from the process, as per the project referred to here, but at the moment that's all they are, ideas...

I have been accused of 'hating PCs', (not on this forum, but elsewhere), not true. Why do others design and build amateur radio transmitters and receivers themselves when they could easily go out and buy them? Because they want to, they can, and therefore do.


Theres nothing wrong with using it as a tool test gear to show your gear works i just hate the cutting out of the building part altogether and there gos your hobby the ham s just used what was built for a use to chat and show images over distance that was their main interest not the idea of it that would as shown to be discarded at the next new idea next cheaper device Hams are very fickle people ! well most must be the odd exception out there .....
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: Vintage SSTV transmit converter

Postby Harry Dalek » Thu Feb 15, 2024 8:41 am

acl wrote:
Screenshot 2024-02-13 161637.png


Harry,

I have checked the schematic against the PCB and everything appears correct. Check U17 pin 4 is at +12 volts and 11 at -12 Volts dc . Verify pin 5 U17c can be adjusted from zero to +2.1 Volts with VR5 (white). When voltage on pin 6 U17C rises above the threshold set by VR5. try with VR6( black) at max. If not 'lift R45 and see if it clears.


I will try it today Chris ,i had no time yesterday and today has ended the same way just have to do a few things around town i thought ! . Thanks for the advice i will give it a go. i did buy a new Opamp to make 100% sure its not that again and a few new TTLs ...rather pleased about that as the fellow at jaycar was a bit out of it and gave me more than i asked for and gave the lot to me cheaper as well win win that made my day .
I did check the dual voltage pins are all correct and ground getting 0 to 2.3v on pin 5 still looking at R45 now raising its value decreases the 566 frequency the problem seems to be at 10lk R48 with the 10nf to pin 10 of U17D signal level is fine out of 566 pin 4 to that 10 k R48 but on the cap side signal very low i see the frequency from the 566 is to high and this is a filter i will have to see if i can now drop the 566 frequency to the correct range might pass it passed via u17D then/a job for tomorrow !
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: Vintage SSTV transmit converter

Postby Harry Dalek » Fri Feb 16, 2024 6:02 pm

Interesting tests today it seems i am off on the 555 clock frequency and it is critical and i am not sure yet what that is i was setting it close to what was said in the project but it seems off or i have something wrong i will check this tomorrow .
I have adjusted the clock to get as close i could to one frame but best i could do today is the shown off frequency results with out changing the 555's cap or trimmer that best i can do as shown ...Started off check the grey bar which i didn't take a picture of but i knew then it would work .
Swapped then to an old mini dvd recorder camera which outputted the video with a cable i had .
DSCN9663.JPG

I found the out put from the U17d low as it is was what was expected viewing the results on MMSSTV i also found adjusting the white black controls are easier just viewing a transmitting a picture and adjusting them .
Close enough today for check how close i could get to seeing something ....not great but very very hopeful now
Below is me not that you can see much of my head in this multiple low def images
DSCN9655.JPG


Next two i tried to get as close to getting it to showing one frame at a time but my settings can only do the below so far so i know the video part is working now again i will work on the clock tomorrow ..i did by the way have to increase R45 the 15k to 180 K that lowered the 566 frequency into a range between 1 and 2 KHZ
Getting there !
I am wondering what ever the correct frequency is on the 555 it would be good if that oscillator was synced from the crystal clock or the line pulse to stop drift the 555 does wonder off frequency a touch i would expect slewing in the frame on switch on or in time of use ..i think you can sync off a different frequency ?
Any case just thinking about it see how it gos when its fully working



DSCN9665.JPG

DSCN9667.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: Vintage SSTV transmit converter

Postby Harry Dalek » Sat Feb 17, 2024 7:42 am

Going to be working on the 555 clock today so i can display one image but got my first Recognisable test card up this morning ...sorry about the mess!
The 555 is at 3.826 khz on this multiple image
Attachments
DSCN9670.JPG
DSCN9673.JPG
DSCN9679.JPG
Last edited by Harry Dalek on Sat Feb 17, 2024 8:04 am, edited 3 times in total.
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Re: Vintage SSTV transmit converter

Postby acl » Sat Feb 17, 2024 7:45 am

Looking good Harry.
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Sat Feb 17, 2024 8:08 am

acl wrote:Looking good Harry.


Thanks Chris yes very hopeful now see if i can do better with a bit of work on it today ...check in later i will post up results
EDIT
Well not really worth the posting what i got up to today ,i thought it would be an easy exercise to adjust the 555 to display a single frame not so best i could do is 2 or 3 per frame started to run out of light for all this as well .
There's a bit of noise in the video i think due to the low light levels so gave up today had better results in the morning
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: Vintage SSTV transmit converter

Postby Harry Dalek » Sun Feb 18, 2024 3:21 pm

Well i think i have more problems than i thought ,checking my grey bar test card i don't seem to be able to display greys only the 2 ends black and white seem to show up very limiting to what i can test i will have to have another look at if U16 is playing up ..so young Grogu here only the eyes shadow shapes show up ..I noticed greys when i started doing testing a day or 2 back but something is up now .
Attachments
DSCN9680.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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Vintage SSTV transmit converter

Postby acl » Mon Feb 19, 2024 4:13 am

Hi Harry,

I'm sure you are not too far away. Just check with grey scale generator the input to the ADC chip is in range 0 to 5 volts and look at the outputs D0 to 7 are clean switching between loic 0 and 1 . There is a fair degree of noise on the picture. Check your resistor chain values are correct.

Regards Chris
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Mon Feb 19, 2024 7:41 pm

acl wrote:Hi Harry,

I'm sure you are not too far away. Just check with grey scale generator the input to the ADC chip is in range 0 to 5 volts and look at the outputs D0 to 7 are clean switching between loic 0 and 1 . There is a fair degree of noise on the picture. Check your resistor chain values are correct.

Regards Chris


Hope so Chris thanks for the advice ,i will look into testing that procedure .
I have been thinking it over the 2 main problems so far what is mentioned above with your solution and the other i still don't think i am displaying correctly ,best i have been able to display least amount of images per frame is 2 or 3 images per frame i think with the the 555 frequency at about 1.913khz ,1.278 ,the wanted reading of 2.327 KHZ does not seem to work its way out of sync if i try it that's a little confusing to me why results differ .
I am thinking there is some sort of timing mistake i have tried every frequency from 300 hz to 8khz there is not a single frequency that will display a single frame the 2 shown are pretty much best i can do .
The voltage into the ADC reading is on the contrast adjustment only i forgot to try brightness but reading was 2.5 to 3 volt i will check with the brightness control again
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: Vintage SSTV transmit converter

Postby Steve Anderson » Fri Feb 23, 2024 5:51 pm

Just a suggestion, assuming the 625 video signal is a standard 75 ohm arrangement, most cameras, VCRs etc.,try putting a 82 ohm resistor in parallel with the outer two terminals of the 1k pot, VR1, i.e. across the input connector. This will present a close approximation to 75 ohms which the source is probably expecting and reduce the input voltage to around 1V p-p. I assume this was an omission.

The following circuit (Q1-3) has quite a lot of gain which may be overloaded. Though this could be circumvented by adjusting VR1 towards its earthy end. With no input signal the emitter of Q3 should sit around +2.5V, adjust with VR2. The same point with no input should vary from about +0.6V to +5.0V (perhaps a little more) over the range of VR2.

Steve A.
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Fri Feb 23, 2024 8:52 pm

Steve Anderson wrote:Just a suggestion, assuming the 625 video signal is a standard 75 ohm arrangement, most cameras, VCRs etc.,try putting a 82 ohm resistor in parallel with the outer two terminals of the 1k pot, VR1, i.e. across the input connector. This will present a close approximation to 75 ohms which the source is probably expecting and reduce the input voltage to around 1V p-p. I assume this was an omission.

The following circuit (Q1-3) has quite a lot of gain which may be overloaded. Though this could be circumvented by adjusting VR1 towards its earthy end. With no input signal the emitter of Q3 should sit around +2.5V, adjust with VR2. The same point with no input should vary from about +0.6V to +5.0V (perhaps a little more) over the range of VR2.

Steve A.


Steve any suggestion is welcomed at the moment since the last posting things have gone down hill on the video part of it i will for sure give the 82 ohm resistor a try tomorrow.
I have been looking at the problem over the last few days and what i was not expecting even a LS type IC can give different results to the another LS brand and of a different age, i was thinking so long as it was a LS it should be the same i wanted to test this with what i had built with some modern replacement LS versions i just got and it pretty much started to play up ! .
Now i am trying to replace them to the original LS versions to working state again .
Even so the timing is off shown at the 555 correct framing frequency no where close to its project adjustment .
I will have a look at running this with a bench power supply it has a larger transformer just see if i was pushing it with what i was using .
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: Vintage SSTV transmit converter

Postby Steve Anderson » Sat Feb 24, 2024 12:37 pm

Ah yes! The old "Underestimating The PSU" trap, many fall into it, including myself. A cursory glance at the circuit I would guess something like 300 to 500mA at 5V would be about right, plus 100mA on the +/-12V rails. A very very rough guess, it might be considerably less though. If it were changed to using HC devices, maybe 50mA for the 5V. But I don't suggest that at this stage. An indication of this is the size of the supply used in the EA article.

...and that's just the average current. Even an innocent-looking 555 can draw over 100mA for a short period as it switches. This can pull down the +5V rail to below the +4.75V limit for LS devices causing them to misbehave before the regulator has a chance to respond. My usual rant r.e. supply bypassing and heavy-duty earth/grounds shouldn't need repeating. The answer, put a large (100uF+) cap on the output of the regulator in addition to all the 10n/100nF bypass/decoupling caps.

In many articles published problems DIY builders have eventually get traced back to the supply arrangements. The consensus generally of misbehaving DIY projects is power supply problems are 90% of them.

If the regulator(s) is/are not on the board (e.g. bolted to a metal chassis), place those large-ish caps on the board. The regulators don't need them, the circuit does. But I still place 100nF disc-ceramic caps on both the input and output of 78xx/79xx regulators within 1cm of them wherever they may be, these are for stability such that they don't oscillate. Consider them essential. They cost peanuts, especially if you buy 100 or more at a time. You will (or should) use them up quickly.

The same applies generally to variable regulators (e.g. the LM317/LM337 varieties), but follow the datasheets if in doubt.

Steve A.

A link that outlines the reasons and techniques often used...

https://en.wikipedia.org/wiki/Decoupling_capacitor

In the photos you can see how seriously these manufacturers take this!...and with good reason!
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