Slow Scan Television Experiments

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: Slow Scan Television Experiment

Postby Steve Anderson » Fri Nov 21, 2014 3:32 pm

Simple 1.2kHz band-pass filter knocked-up and it confirms that there is the proper syncs for both line and frame. Trace below shows the baseband video with the broad frame sync in yellow. In cyan is the output of the filter - not bad for such a simple arrangement (see below).

I had a dig through the MMSSTV (un)help file and although it does list the 8kHz rate I used yesterday it's labelled as 'secondary'. The default seems to be 11025Hz (damn audio CDs).

Steve A.
Attachments
SSTV Simple Sync Filter 1.gif
SSTV Simple Sync Filter 1.gif (5.96 KiB) Viewed 5813 times
SSTV Simple Sync Filter 2.gif
SSTV Simple Sync Filter 2.gif (3.21 KiB) Viewed 5813 times
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Re: Slow Scan Television Experiment

Postby Steve Anderson » Fri Nov 21, 2014 4:41 pm

I'm not sure what the difference there is between a .mmv file and a .wav one. But I simply re-named the file extension from .wav to .mmv that I posted yesterday and got exactly the same results.

Repeating the exercise at 11025Hz results in a perfect picture except for the slant and it never seems to find the frame sync...odd.

It's exactly the same on the 'live' input to the soundcard instead of a file playback...

I also tried RX-SSTV and it's also the same...but it uses the MMSSTV engine so no surprise there...

Installed ChromaPix and it too is almost exactly the same - I cannot fathom what's wrong!

Steve A.

A bit later...I've often seen references to the 'Robot 8 second B&W mode' referrred to as, "Similar to the original SSTV specification". Now, a lot of this software calls it 'Robot 8 sec B&W"....so what's the difference between it and Copthorne McDonalds' specification? I've Googled 'til I'm blue in the face, but nowhere can I find the Robot spec for this mode. It must be a slight difference as the various software I'm using is 'almost there'.

The answer may be in getting this software into transmit mode and reverse-engineering the signal. It may be a lot of work, maybe not.

What I am generating is pure Copthorne McDonald SSTV...

It could be similar to the difference between the original Baird mechanical television spec and the NBTVA version.
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Re: Slow Scan Television Experiment

Postby Harry Dalek » Fri Nov 21, 2014 6:52 pm

Steve Anderson wrote:I'm not sure what the difference there is between a .mmv file and a .wav one. But I simply re-named the file extension to .wav that I posted yesterday and got exactly the same results.

Repeating the exercise at 11025Hz results in a perfect picture except for the slant and it never seems to find the frame sync...odd.

Steve A.


Thats good Steve one problem out of the way !

Have you tried it on Chroma pix SSTV ,theres a lock and resync buttons when you select 8 sec sstv on MMSSTV bottom of viewing screen...also Auto which you might be using ?

Yes i have no idea what the difference is on robot 8 or 8 sec its called robot on Chroma pix seemed to give the same results when using it !

BTW why does the stair case signal reverse in the screen grab of it ? half screen one way and reversed ?
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Re: Slow Scan Television Experiment

Postby Harry Dalek » Fri Nov 21, 2014 7:43 pm

This screen grab doesn't really show any thing yet my line mirror is a little off frequency but doing the first tests with the head amp and line mirror working this is the very first try so i kept it .
Wasn't even pointing the line mirror at any thing just wanted to see if the head amp could pick up a mirror reflection when it was rotating which i though was at line speed but its a bit off.
i am going to adjust the line mirrors speed and get it in sync.
Trying it with more light i am very hopeful what i am seeing ,i have no lens system so i will see if i can get any thing recognizable out of it in coming tests .
Once again fingers crossed
Attachments
Screen 00030.jpg
first ever try with the line mirror
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Screen 00032.jpg
room ?
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Screen 00033.jpg
cleaner signal
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Last edited by Harry Dalek on Fri Nov 21, 2014 9:37 pm, edited 2 times 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: Slow Scan Television Experiment

Postby Steve Anderson » Fri Nov 21, 2014 7:44 pm

OK, a number of developments since my last post...

I made a start on the transmit side of MMSSTV....and quess what? In 8-second B&W mode it sends a VIS code! So I assume that it expects one when in receive...that's probably the reason for, a) the slant, b) the lack of frame sync. So my presumption is that this doesn't work with the Copthorne McDonald spec signals. And I would guess most other software too.

You may recall that I said my use of MMSSTV was going to be a stop-gap measure...that gap has now passed...

For this real basic original SSTV we need to find some 70s-80s DOS-based programs...if that's possible these days - I wish I hadn't got rid of my old 486 a few years ago!

***************

Yes, the signal does reverse. Line 1 has the 30ms frame sync, the rest of the line is peak white.
Lines 2-60 inclusive have a 5-level decending staircase (white-black).
Lines 61-120 inclusive have the reverse.

This should make it obvious if you've achieved frame sync...or at least that was the idea...

So I'm now in a quandary as to what to do.

For what it's worth I attach the same video but at 11025Hz but I suspect its not going to sync...now removed...

Steve A.

P.S. I did try ChromaPix - exactly the same...
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Re: Slow Scan Television Experiment

Postby Harry Dalek » Fri Nov 21, 2014 8:32 pm

Steve Anderson wrote:
I
made a start on the transmit side of MMSSTV....and quess what? In 8-second B&W mode it sends a VIS code! So I assume that it expects one when in receive...that's probably the reason for, a) the slant, b) the lack of frame sync. So my presumption is that this doesn't work with the Copthorne McDonald spec signals. And I would guess most other software too.


A VIS code steve ? must of been a first in playing with the original system ! and boy it never ended .

You may recall that I said my use of MMSSTV was going to be a stop-gap measure...that gap has now passed...


OH ok you need an original SSTV program

For this real basic original SSTV we need to find some 70s-80s DOS-based programs...if that's possible these days - I wish I hadn't got rid of my old 486 a few years ago!


Well thats sort of easy in that Its JVfax that i recall i used jvfax 7.0 does 8 sec there might still be earlier versions of the program than that ...i found this old site but i think most of the links have died but gives you an idea what to search for .http://ok1ike.c-a-v.com/soubory/soft/sstv_soft.htm

This one has down loads
http://www.forumradioamatori.it/downloa ... /SSTV.html


Seemed to be heaps on SSTV in the past ,i used jvfax in the dos days .

The new wav file worked Steve as you see :)
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Screen 00031.jpg
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Re: Slow Scan Television Experiment

Postby Steve Anderson » Fri Nov 21, 2014 10:21 pm

Yep, it 'works', but without the VIS code it's never going to sync-up. Your results there are identical to mine, the slant and no frame sync. Yesterdays problems were simply an unsuppoted sample rate...even though it's mentioned in the (un)help(ful) file.

So, what to do? Certainly between the two of us we could continue to use 'dinosour mode' but for the greater unwashed plan for VIS codes? Maybe?

I need to find out more about VIS codes, e.g. is a VIS code sent at the start of every frame? Or just the first one if you're sending a continuous series of them? They're not that hard to imlement, just a pain in having to fart aroud with the code I have already written.

Me, myself and I prefer 'dinosour mode'.

I've had so many problems in trying to get DOS programs to run in the 'Doze DOS box I'm not going to even bother unless I can either find a DOS-only PC, or even a spare unused machine, or get the 'Doze PC to dual-boot. I still have DOS 5.00 and 6.22 disc images.

But thanks for the links anyway, some old memories amongst them...

Steve A.
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Re: Slow Scan Television Experiment

Postby Harry Dalek » Fri Nov 21, 2014 11:15 pm

Steve Anderson wrote:Yep, it 'works', but without the VIS code it's never going to sync-up. Your results there are identical to mine, the slant and no frame sync. Yesterdays problems were simply an unsuppoted sample rate...even though it's mentioned in the (un)help(ful) file.

So, what to do? Certainly between the two of us we could continue to use 'dinosour mode' but for the greater unwashed plan for VIS codes? Maybe?

I need to find out more about VIS codes, e.g. is a VIS code sent at the start of every frame? Or just the first one if you're sending a continuous series of them? They're not that hard to imlement, just a pain in having to fart aroud with the code I have already written.

Me, myself and I prefer 'dinosour mode'.

I've had so many problems in trying to get DOS programs to run in the 'Doze DOS box I'm not going to even bother unless I can either find a DOS-only PC, or even a spare unused machine, or get the 'Doze PC to dual-boot. I still have DOS 5.00 and 6.22 disc images.

Steve A.


I like the original too ,I was thinking Robot mode was just calling 8 second a new name for monitors made at the time .
I found dos Jvfax works in windows 7 i tried some of the others i could down load but they all just about crashed locked up i would like to see one that does 7 seconds mmsstv does 12 and 36 also.
Its more than likely best to stick with the original mode less of a headache and keeps it alive.
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Re: Slow Scan Television Experiment

Postby Steve Anderson » Fri Nov 21, 2014 11:28 pm

Harry Dalek wrote:...best to stick with the original mode less of a headache and keeps it alive.

I agree there, but I feel that it would be an uphill struggle. It's all too easy these days, all you need is a PC, a commercially made transceiver and knock-up a simple interface between the two. You can probably buy that as well anyway. No challenge or satisfaction, instant gratification, though I don't mean to pour cold water on the efforts and strides that have been made in the last few decades for those who have developed and spent much time and effort on this.

Dr Ralph Taggart is one of the early exponents of SSTV and he's a member here. I wonder what his thoughts might be? If he's watcthing this he may have some input, we'll see.

Much like mechanical TV, I'm more interested in the roots of where this came from. 30-line TV developed (in the UK) to 405, then 625, then colour, now HD. So, it's a similar progression. But there are those (albeit a small number) who want to preserve these older modes. They have a place in history. The '405 alive' society is an example (purely British of course) and Steve Ostler may update us on his groups efforts to get 405 occasionally radiated around London. I'm sure likewise there are those in France and Belgium who want to keep the 819 standard going.

When I explain to my niece that when I was her age (late teens) there was no colour TV, no mobile phones, no Internet. She's incredulous. (Try and prize a mobile phone out of a teens hands today!). And few, if any, had credit cards. ATMs - forget it! If you missed the 3:30pm deadline at the bank you had to wait until tomorrow, or Monday.

Rotary dial telephones...something I think my niece would have no idea how to use without instruction.

Anyway, the day is drawing to a close for me...

Steve A.
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Re: Slow Scan Television Experiment

Postby M3DVQ » Sat Nov 22, 2014 12:16 pm

The slant is caused by the clock rate being inaccurate. You can adjust an offset to get it right using an accurate clock source, but usually the problem is caused by the default sample rate being a division of 44100Hz (iirc it is 11025) which modern soundcards don't do so it is resampled causing a small error offset.
If you set the sample rate to a division of 48000 (or indeed just 48000) I wouldn't be surprised if the slant goes away. If you've had auto slant correction enabled be sure to set the slant back to 0.

All Makoto Mori's programs have their defaults set to obsolete sample rates. It took a long while to figure out why no-one could get accurate frequency settings for BPSK and lots of faffing about with the offset adjustment to get TX on the same frequency as RX! :evil:
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Re: Slow Scan Television Experiment

Postby M3DVQ » Sat Nov 22, 2014 12:27 pm

As for starting without VIS tones, that shouldn't be an issue... With the correct sample rate set I can record an 8 second B&W image, trim off the start and end of the recording, and play it back into MMSSTV and it auto starts, auto syncs, and there's zero slant :)
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Re: Slow Scan Television Experiment

Postby Harry Dalek » Sat Nov 22, 2014 12:33 pm

Steve Anderson wrote:I agree there, but I feel that it would be an uphill struggle. It's all too easy these days, all you need is a PC, a commercially made transceiver and knock-up a simple interface between the two. You can probably buy that as well anyway. No challenge or satisfaction, instant gratification, though I don't mean to pour cold water on the efforts and strides that have been made in the last few decades for those who have developed and spent much time and effort on this.


Yes when i lost interest in SSTV it got to the point you had to buy something to watch it ,i know it has to evolve but the original system you could make every thing if you wanted to do it ,its like buying a iphone these days you have no hope making one, but if you want it you have to buy it ,its more the want of the device than any interest in how it works .
I think the days of B/W 7 or 8 sec are gone for Hams but here thats another story one good thing about the internet is like the line in Jurassic park life will find a way !

Dr Ralph Taggart is one of the early exponents of SSTV and he's a member here. I wonder what his thoughts might be? If he's watching this he may have some input, we'll see.


OH thats good i didn't know Ralph was into slow scan yes it would a good to have Ralph's thoughts .

Much like mechanical TV, I'm more interested in the roots of where this came from. 30-line TV developed (in the UK) to 405, then 625, then colour, now HD. So, it's a similar progression. But there are those (albeit a small number) who want to preserve these older modes. They have a place in history. The '405 alive' society is an example (purely British of course) and Steve Ostler may update us on his groups efforts to get 405 occasionally radiated around London. I'm sure likewise there are those in France and Belgium who want to keep the 819 standard going.


I don't think there is one for early slow scan or that matter early fax i come across people here and there with some interest but i have not heard of a group like here for NBTV which is funny as SSTV has more of an interest world wide.

When I explain to my niece that when I was her age (late teens) there was no colour TV, no mobile phones, no Internet. She's incredulous. (Try and prize a mobile phone out of a teens hands today!). And few, if any, had credit cards. ATMs - forget it! If you missed the 3:30pm deadline at the bank you had to wait until tomorrow, or Monday.


:lol: Yes all we had were encyclopedias for an internet and radio and b/w tv the thing is if you never had it you would not miss it now theres no going back ,i hate to think whats coming !

Rotary dial telephones...something I think my niece would have no idea how to use without instruction.

Anyway, the day is drawing to a close for me...

Steve A.


OH that was a bit like me when i got my first smart phone i only had a flip phone last year :wink:
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Re: Slow Scan Television Experiment

Postby Harry Dalek » Sat Nov 22, 2014 5:46 pm

Well i wasn't getting far in todays experiments with one or both mirrors getting shapes but nothing i could really tell either way more a guess bit like the pictures i posted a while back .

I then tried the test card and the line mirror holding the head amp sensor in one spot then what ever it sees is repeating down the scan that sort of worked as you see picture not really a 100% it works but perhaps .

My last experiment is giving me some hope i am on the right track .

I figured well i will try it the old fax way or a bit of a reverse of my mechanical sstv i would have to get some thing this way or i would have no hope with a mirror reflection .

So i made some paper cylinders and drew this and that on them ,one placed it over the line mirror and let it rotate ,hand scanned down with the head amp light sensor and bingo it started to show the image not great but there.

I am sort of glad i did this as it looks to me i am not running at the right line speed mmmmm seems to me its only half i will have to look into this i would think 15 hz is right running the 4 mirror sides across an opto switch but i can count the lines and its not 120 perhaps the hand scanning was off. :wink:

See pictures below any one trying any thing like this should give it a go when i get back to the NBTV mirror camera i will see if i can use an idea some thing like this for a test for the line motor .

I do know now the head amp is spot on in just about any light level with no artificial room light needed ,it was a cloudy day again today but half and half so light levels in the room were jumping both ways its way it was just a matter of readjusting the head amp gain control .

I'll post a video when i drop its size/
Attachments
IMG_0008.JPG
The test card reflection test bit off sync
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IMG_0012.JPG
MY sstv cylinder idea
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Screen 000400.jpg
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Screen 00041.jpg
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Re: Slow Scan Television Experiment

Postby Steve Anderson » Sat Nov 22, 2014 6:45 pm

M3DVQ wrote:The slant is caused by the clock rate being inaccurate....With the correct sample rate set I can record an 8 second B&W image, trim off the start and end of the recording, and play it back into MMSSTV and it auto starts, auto syncs, and there's zero slant

Thanks so much for your input. There is a vague memory I have of reading about this some time (years) back.

I've had a fiddle around with MMSSTV with you comments foremost, but I cannot find the correct calibration 'knob'. This is a live analogue input generated electronically fed straight into the PCs line input, it's not recorded or processed in any manner.

The clock accuracy you are referring to, is it the soundcard clock? The PC clock? Or the clock the generates the SSTV signal itself? I have been assuming the 'knob' for this is within MMSSTV, maybe I'm wrong there.

As per your suggestion I recorded 60 seconds of the generated SSTV signal at 12000Hz sample rate using 'Audacity' on a Windows XP machine. If you can quickly play it and let me/us know what you find. Please don't spend much time on this. This .wav file has been nowhere near MMSSTV at all.

Thanks in advance,

Steve A.
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Re: Slow Scan Television Experiment

Postby gary » Sat Nov 22, 2014 6:57 pm

Steve are you recording at the sound card's native sample rate (usually 48k) or an integer multiple thereof? If not there will always be a slight sample rate inaccuracy due to the way the sample rate conversion is done on modern sound codecs.

If the app you are using doesn't give you the option of recording at the correct rate then use another app to record at that that rate and resample using, say, Audacity, and feed the audio in as a file (if possible) rather than straight from the sound card - if nothing else it will prove the point.
Perfecting an NBTV system is like trying to slam a revolving door...
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