48 line 64 line Conversion

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Re: 48 line 64 line Conversion

Postby Harry Dalek » Thu Jun 22, 2017 12:25 pm

Steve Anderson wrote:Harry, I meant R704 and R724, my mistake again! In a rush as ever these days.


No problems Steve i was going to look into it after i post up these readings in the last post .

Assuming you've got those two resistors right for 400Hz and 12.5Hz it should be possible to work out their value at other rates. Say a 750Hz line rate.


I have to point out my little scope frequency meter accurate up to a point on low readings i couldn't do a 12.5 only 12hz adjustment ...you will notice the readings are close to what is expected on the line frequencies but i was adjusting the frame as i was not sure of the correct line frequencies till now .
Any case the locking to the line frequencies is close so that part must be working up to 64 line 120 line its not at all happening .

If 400Hz required a resistor of 12k then for 750Hz it should be 400/750*12k = 6k4, try a 6k8 first.

In the other direction where you want to slow things down...say 12.5Hz needed 15k, and you want a frame rate of 6.25Hz, 12.5/6.25*15k = 30k, try 27k or 33k. 30k can be approximated by 33k||330k.

Steve A.

[/quote]

Oh i see the change for 750 hz 60 line ...ok i can try that and see .....just trying to work it out if am correct for a line rate of 120 3khz it would be 1.6k resistor ?
The frame rate should change as before but i will leave that for now and see what the change does for Garys 60 line .
Yes swapping the sawtooth to the deflection amps does sound like a better idea when i get around to it .
i am home today so i will try the line rate resistor change now ...think i will look for a multi switch for this as it will be needed
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Re: 48 line 64 line Conversion

Postby Steve Anderson » Thu Jun 22, 2017 12:33 pm

The other issue may be that in swapping the inputs to the deflection amps the scan is in the wrong direction, so be prepared for that. It may mean a simple op-amp per axis if required.

Now, R704/724, you don't want these to give you 400Hz with no input, the free-running frequency should be slightly lower than the nominal, say 350Hz in a 400Hz application. The others, pro-rata.

12.5Hz is 80ms, this should be 8 horizontal divisions on the scope screen at 10ms/div. Easier than using the frequency counter.

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Re: 48 line 64 line Conversion

Postby Harry Dalek » Thu Jun 22, 2017 2:50 pm

Steve Anderson wrote:The other issue may be that in swapping the inputs to the deflection amps the scan is in the wrong direction, so be prepared for that. It may mean a simple op-amp per axis if required.


Yes i am expecting a pain in more switching i have room if another circuit is needed ...that ok bit at a time get there .

Now, R704/724, you don't want these to give you 400Hz with no input, the free-running frequency should be slightly lower than the nominal, say 350Hz in a 400Hz application. The others, pro-rata.
[/quote]

Yes mine was a bit low half that infact i will double check that capacitor on the line oscillator .

12.5Hz is 80ms, this should be 8 horizontal divisions on the scope screen at 10ms/div. Easier than using the frequency counter.

Steve A.


I will check with that next test Steve thanks .
I tested the change but selected a 64 line video by mistake so it still works at 800 hz i will go back later and check with a 60 line .
have not changed the frame sawtooth yet the good thing on this multi position switch i think it has independent positions so i can use the same switch to switch both the frame and line resistors on the same multi position switch.


youtu.be/nzO-bqTIcl4
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Re: 48 line 64 line Conversion

Postby Klaas Robers » Thu Jun 22, 2017 6:07 pm

About the vertical fly back line: I have seen on the wave form diagrams that you posted, that the first video lines are white, not a stair case. That is the best way to make that fly back line visible. I don't understand why these lines are made white and not black.

In CCIR scanning 625 lines, there are some black lines following the vertical sync. This makes the fly back already almost invisible in the first simple black and white TV's. Later TV's suppressed the video signal during the fly back. Then the vertical sync pulse is combined with the video to make the video black during fly back. This is the signal that drives the transistor TR701 that "shorts" the sawtooth capacitor via the resistor R702 (39 ohm) in your diagrams.

I did more or less the same in my 1973 SSTV monitor.
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Re: 48 line 64 line Conversion

Postby Harry Dalek » Thu Jun 22, 2017 7:47 pm

Klaas Robers wrote:About the vertical fly back line: I have seen on the wave form diagrams that you posted, that the first video lines are white, not a stair case. That is the best way to make that fly back line visible. I don't understand why these lines are made white and not black.


Its the first time i have had to think about this its a problem seems fixable but adjusting the monitor does make it fainter i am not overly fussed about it at the moment ,i suppose if it were black we would have the other problem over white i think ?


In CCIR scanning 625 lines, there are some black lines following the vertical sync. This makes the fly back already almost invisible in the first simple black and white TV's. Later TV's suppressed the video signal during the fly back. Then the vertical sync pulse is combined with the video to make the video black during fly back. This is the signal that drives the transistor TR701 that "shorts" the sawtooth capacitor via the resistor R702 (39 ohm) in your diagrams.

I did more or less the same in my 1973 SSTV monitor.

[/quote]

OH i see Klass i was lucky with your help with mine as it didn't really show up well not so far fingers crossed but here on the NBTV one over 32 lines it is but i will work on it in time i am happy its doing up to 64 lines and is able to display a few 60 line systems now .
The circuit change Steve does seem to work....... on the frame R704 i just put a trimmer at the moment i will try your resistor change i hope tomorrow any case does seem to help .
Theres still an issue with 60 line with shade changes as you see in the 3rd moving video its on its side as its Garys 60 line horizontal ..there might be an issue with my sound card as i know one of the channels was playing up the Gary video files seem to need a higher sound card level might not work if i tried a laptop as with the 3BP1.
Well getting better better than it was yesterday :D

youtu.be/3rdYIMO1mgo 48 line

youtu.be/0BfjJJiLGUM 64line

youtu.be/KUy3EWfkM6I 60 line gary

youtu.be/7IL_yIEPYzA 60 line gary

youtu.be/xTmXNg7XWXo 64 line NBTVA standard
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Re: 48 line 64 line Conversion

Postby Klaas Robers » Thu Jun 22, 2017 10:36 pm

You won't have a problem with a black, or blanked fly back line, as the fly back line is written on top of the written normal lines. So a black fly back line is invisible, a white fly back line is visible.

I also see on the left top corner of the picture, a single line that runs above the picture, vertically upwards. This is well understandable, because:
- the most left line is written, from bottom to top,
- then there is NO line sync pulse,
- so the scan continues and goes more upwards,
- then the missing sync pulse detector detects that there is no sync pulse (time out),
- the horizontal scan starts to fly back,
- this fly back is invisible, because out of the screen area,
- then the line oscillator automatically flies back to the bottom
- and starts a new line
- and you see a white slanted fly back line starting at the bottom,
- but then the sync pulse at the end of line 1 comes
- and you see the remaining part of the fly back line starting again at the bottom of the picture.
So everything behaves as it should do, as you made it.

The visible fly back line at least shows us what happens. When it was blanked, you would not see it and it was impossible / more difficult to see the behaviour of your circuits. So keep it in this way.

What you coud do is making R702 somewhat smaller in value, e.g 22 ohm or 10 ohm. Then the fly back line should be still slanted, but more horizontal, faster.
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Re: 48 line 64 line Conversion

Postby Harry Dalek » Fri Jun 23, 2017 12:38 pm

Klaas Robers wrote:You won't have a problem with a black, or blanked fly back line, as the fly back line is written on top of the written normal lines. So a black fly back line is invisible, a white fly back line is visible.


HI Klass
I have that alright yes very visible on the Tasmanian devil 64 line video below that is logical black would be invisible !
The sync part of the circuit Steve told me is your design ,i have not come across the original is it in the old newsletters ?

also see on the left top corner of the picture, a single line that runs above the picture, vertically upwards. This is well understandable, because:
- the most left line is written, from bottom to top,
- then there is NO line sync pulse,
- so the scan continues and goes more upwards,
- then the missing sync pulse detector detects that there is no sync pulse (time out),
- the horizontal scan starts to fly back,
- this fly back is invisible, because out of the screen area,
- then the line oscillator automatically flies back to the bottom
- and starts a new line
- and you see a white slanted fly back line starting at the bottom,
- but then the sync pulse at the end of line 1 comes
- and you see the remaining part of the fly back line starting again at the bottom of the picture.
So everything behaves as it should do, as you made it.


Its good its working as it should i find its much tighter to sync at 60 64 than 32 anf 48 line the mono circuits for locking the frame must be working to a point i know its not the same as the quick locking you get at 32 line must be very sluggish here some timing must be off i think .

The visible fly back line at least shows us what happens. When it was blanked, you would not see it and it was impossible / more difficult to see the behaviour of your circuits. So keep it in this way.[/quote

OK will keep as will not fiddle here ...

What you coud do is making R702 somewhat smaller in value, e.g 22 ohm or 10 ohm. Then the fly back line should be still slanted, but more horizontal, faster.


Oh ok i will try that tomorrow have to go out to day but have time then that will be interesting to see i will show results


youtu.be/MWpN0VFwkd4
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Re: 48 line 64 line Conversion

Postby Andrew Davie » Fri Jun 23, 2017 4:16 pm

Very good and fascinating to watch.
It made me wonder - I haven't seen much of any discussion about the 1930s competition between Baird's mechanical system and (was it EMI?). The point being, I really wonder just what the CRT image they were demonstrating back then actually looked like. Of course by the mid-late 1930s CRT displays were pretty good. But how good were the first ones in that competition? Do we have any modern examples/analogs to demonstrate? Perhaps using a tube from that time, and what we know about the techniques used back then....
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Re: 48 line 64 line Conversion

Postby Harry Dalek » Fri Jun 23, 2017 8:19 pm

Andrew Davie wrote:Very good and fascinating to watch.
It made me wonder - I haven't seen much of any discussion about the 1930s competition between Baird's mechanical system and (was it EMI?). The point being, I really wonder just what the CRT image they were demonstrating back then actually looked like. Of course by the mid-late 1930s CRT displays were pretty good. But how good were the first ones in that competition? Do we have any modern examples/analogs to demonstrate? Perhaps using a tube from that time, and what we know about the techniques used back then....


Hi Andrew
I only have seen one 120 line image below may be Steve O has one up on the forum on he's monitor this is in colour so must be may be an old set perhaps fired up for the photo .
The Baird and emi was 240 line Baird and 405 line emi ...there was a bit in between systems in Europe I know watching TV is King documentary in the 90s most CRT's were Green as the Devil but the English invented the true b/w phosphor they were saying that it was not possible the Germans in the 30's could not have made a b/w phosphor just rather the green for their own reasons at the time
Yes it is interesting that is why i would like to try up to 120 line nothing more than to have done it at least ...
I will more than likely stop with this one at 120 and make another for 120 and over might be pushing it here with this one ,and doing it in stages i might get there or at least i can try which i enjoy .
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Re: 48 line 64 line Conversion

Postby Klaas Robers » Fri Jun 23, 2017 8:42 pm

EMI (indeed) started in 1937 with a CRT-system with 405 lines. That suggests that they could could show a resolution of 405 lines. However, if you have a picture tube with 405 lines interlaced (the 405 line system was interlaced), then you look to a picturetube with 200 lines, as you will see one field, so lines with a spacing of 200 lines vertical. I don't know the latency of the phosfor then used, when it is slow enough you could still see the interlaced field. So think that they had CRTs with a resolution of about 400 lines.
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Re: 48 line 64 line Conversion

Postby Harry Dalek » Sat Jun 24, 2017 10:24 am

Klaas Robers wrote:EMI (indeed) started in 1937 with a CRT-system with 405 lines. That suggests that they could could show a resolution of 405 lines. However, if you have a picture tube with 405 lines interlaced (the 405 line system was interlaced), then you look to a picturetube with 200 lines, as you will see one field, so lines with a spacing of 200 lines vertical. I don't know the latency of the phosfor then used, when it is slow enough you could still see the interlaced field. So think that they had CRTs with a resolution of about 400 lines.


Just defocusing a touch it looks ok but without the line number loss must give a sharper image i suppose ........interlacing at 6hz not really good at our frame rate for movement .

I am looking into your help with Klass R702 today so see what results it give,s ,might have to put this resistor change on via a switch if it effects also the 32 line a the switch and the parallel resistor to drop the on board 39 ohm can be adjusted then but i will see what happens ...

Some images you as is you don't see the flyback line at all as below but its most of the time that needs fixing up i am very interested to see the results with a change .
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Re: 48 line 64 line Conversion

Postby Harry Dalek » Sat Jun 24, 2017 1:56 pm

No time just now but worked out a way to rid the fly back lines but interesting effect explain later tonight
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Re: 48 line 64 line Conversion

Postby Harry Dalek » Sat Jun 24, 2017 6:09 pm

klass i didn't have any luck lowering the 39 ohm resisitor R702 so i moved on to the Frame sync input i was thinking perhaps the 4.7k R701 might be to low in resistance i placed a 2.2k resistor in series with the 4.7 k and the fly back line at 64 line testing disappeared i then reduced the 2.2k to a 1k in series with the 4.7 again no flyback lines double checking i then removed the input pulse altogether .....i expecting the picture to roll but its still locking interesting i am not sure how this is happening but it is also tried 48 line does the same but not on 32 .

youtu.be/ll9sm1jBxXI
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Re: 48 line 64 line Conversion

Postby Steve Anderson » Sat Jun 24, 2017 7:45 pm

Harry, R702 (and it's conterpart R724) are there to limit the discharge current through the discharge transistor, they should have no effect on timing at all.

The only components involved with timing and ramp amplitude are R704/R724 and C706/C726. That's it. Nothing else.

I'm still vague about the frame and line sync of these other modes apart from the NBTVA 32-line standard. If you could post up the files you're using I'll have a look at them, the format may not be suitable for what you've built so far.

Steve A.
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Re: 48 line 64 line Conversion

Postby Klaas Robers » Sat Jun 24, 2017 8:04 pm

Indeed, the 39 ohm limits the discharge current of the capacitor and defines the fly back time. As I have seen in the 60 lines images fly back takes 2 lines, so you miss 2 lines of video (the first one was launched sky high). And yes, if you have 60 lines, who cares about 2 missing lines, but if they are in the video you want to see them.

So fly back should be as short as possible. Now you can see them you can experiment with them and after they are short enough you may suppress the remains.
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