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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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25th Nov 2022, 8:46 pm | #1 |
Dekatron
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Circuit to display video on analogue scope?
Is there any existing project, or perhaps an old one from a magazine for which the parts are still available, which can take a 625 line / 50Hz mono video signal and display it on an analogue scope?
I appreciate that any scope used for this purpose would need to have a 'Z-Mod' input and an X-Y mode on the timebase. Apologies if this should have been in 'TV and Video' rather than 'Test Gear' but it does rather straddle both genres. |
25th Nov 2022, 9:27 pm | #2 |
Dekatron
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Re: Circuit to display video on analogue scope?
A friend of mine once displayed TV-scan-rate computer video output on his Tektronix 556 by using the 2 timebases of said instrument, a suitable patch cable to feed one of them into the Y input, triggering the timebases off the sync signals and then feeding an amplified version of the video signal into the z-mod input.
For a more normal 'scope you could use the built-in timebase for the line scan. You'd need to provide another ramp generator for the frame scan the output of which would be fed into the Y input of the 'scope. You'd also need to make a sync separator to trigger the internal timebase and the extra one. And the Z-mod amplifier. I wonder if the manual for the Philips EE1007/EE1008 kit might be of use. It's on the obvious Norwegian site albeit only in German (an English version never existed). The EE1007 kit contained a CRT/power supply module, you built the deflection amplifiers, timebases, etc using the standard spring terminals, etc, of said Philips kits. Given that the final project of the EE1008 was a monochrome TV set, albeit using some pre-built modules, it should be possible to deduce a circuit to do what you want. |
25th Nov 2022, 9:52 pm | #3 |
Octode
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Re: Circuit to display video on analogue scope?
This should give you a good start.
https://youtu.be/5FYF5uhCzAM
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Chris Wood BVWS Member |
25th Nov 2022, 10:06 pm | #4 |
Dekatron
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Re: Circuit to display video on analogue scope?
Good point about being able to use the X timebase sweep, I had visualised the circuit needing to do both the X and Y deflection. I'm almost sure one of the magazines did a project for this - I suspect Elektor, they always did go in for the slightly more unusual stuff, but I read it for quite a few years and can't even think roughly what period that would have been.
A lot of the modern microprocessor widgets like Arduinos have multiple PWM outputs which - suitably filtered and amplified - could be used to generate both X and Y deflection. Not many of them have actual D-A outputs, which is a shame. For sync separation possibly something like an LM1881 which can generate TTL sync from Composite video in, although I think it only outputs Composite TTL sync and TTL Vsync (no Hsync, which is strange). There is also a pin compatible 8 pin sync separator which outputs Composite sync, Vsync and Hsync (instead of the odd/even signal of the LM1881) all at TTL level. The part number escapes me at the moment. |
25th Nov 2022, 10:13 pm | #5 |
Octode
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Re: Circuit to display video on analogue scope?
Here is the updated schematic from post #3 https://www.qsl.net/w2aew/W2AEW_NTSC_to_scope.pdf
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Chris Wood BVWS Member |
25th Nov 2022, 10:15 pm | #6 |
Dekatron
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Re: Circuit to display video on analogue scope?
Just caught Chriswood's post with the video link there - and there is the LM1881! That has to be worth a go. What set me off on this, I needed to be able to view a video output from something at work today and found we have no, zero, video monitors on the premises any more. Plenty of computer monitors and scopes though. It set me off wondering how difficult it would be to get a scope to display video.
Chris: Thanks for posting the updated circuit, just caught that as well. |
25th Nov 2022, 10:22 pm | #7 |
Hexode
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Re: Circuit to display video on analogue scope?
When I was a small boy I started work at the BBC where the (then) new Tek 7000 scopes where kept safe in a cupboard because most of the people there preferred to use the simpler Philips scopes that abounded.
After a weekend shift that was very quiet I managed to get a passable picture on one of them using 2 timebases with the TV triggering options and another to invert the video fed to the display's X axis. I think I had 3 hooked up. Needlessly I left them there for the scope guardian to find on the Monday morning. My day off. Ging |
25th Nov 2022, 10:24 pm | #8 |
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Re: Circuit to display video on analogue scope?
I cheated when I did this first I just used the scan and video signals on a small portable solid state TV into my even then ancient Cossor scope.
Would have been 1974 ish Picture was very dim even with the brightness full up and distorted because of the non-linear scan I was picking up from the TV. It was an achievement ........... of sorts. So I find this project appealing. Cheers Mike T
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25th Nov 2022, 11:00 pm | #9 |
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Re: Circuit to display video on analogue scope?
Back in the seventies, it was kind of important to find out what was being done to us on budget days. Boyd and some of the gang at HP decided to rig up a telly. The lab windows looked across the Forth with a good line of sight over to Craigkelly. Two spectrum analysers did the receiving, one tuned to vision, the other to the sound carrier. I'm not sure if they slope-demodulated the UHF FM sound or cheated and tuned to the VHF AM sound.
Scope timebase triggers usually have slow and fast filters, which just happen to be designed around tv line and field rates. You don't need to make a sync separator, you got one for free. One scope triggering on each speed. 'Field' timebase ramp to Y of 'line' scope. Spectrum analyser 'video' to Z of 'line' scope. Contrast was limited. something might have been added to fix the negative picture, or did they change the RF to VHF as well as the sound? Black and green picture on a poky little 8x10cm screen and the whole lab crowded around for the announcement on next years pay restraints... Those were the days. Two spectrum analysers Two 180 series scopes Half a dozen evgineers doing, many more watching them. Same ratio as a building site. David
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25th Nov 2022, 11:45 pm | #10 |
Nonode
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Re: Circuit to display video on analogue scope?
Here's another LM1881 circuit for displaying video on a scope - this one on a Tektronix 465m.
Link which has picture and a video https://hackaday.com/2011/03/30/osci...video-monitor/ and the schematic and more detail https://tubetime.us/index.php/2011/0...video-monitor/ |
26th Nov 2022, 10:14 am | #11 |
Heptode
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Re: Circuit to display video on analogue scope?
There were a number of 'scopes that could display a video picture, one made by Gould known as Post office 18A springs to mind. Dynamco made a plug on timebase module, for the 7100 series, for this purpose as well.
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26th Nov 2022, 10:54 am | #12 |
Dekatron
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Re: Circuit to display video on analogue scope?
Just referring to the PDF circuit posted earlier, there is mention of NTSC - colourwise NTSC/PAL doesn't apply here since the video source will be monochrome but I believe you set the framerate the circuit should expect by alteration of the components on the LM1881 RSET pin.
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26th Nov 2022, 3:49 pm | #13 |
Dekatron
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Re: Circuit to display video on analogue scope?
I notice these examples were top-end scopes. I would guess that getting a decent video bandwidth on the Z channel will be the typical problem.
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26th Nov 2022, 3:53 pm | #14 |
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Re: Circuit to display video on analogue scope?
The Z was also DC coupled in these scopes - done by having essentially dual EHT windings offset to drive grid and cathode of the tube.
David
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26th Nov 2022, 4:51 pm | #15 |
Dekatron
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Re: Circuit to display video on analogue scope?
I did it once with raw video from a VCR and two 'scopes, though one was just used as a field sawtooth generator (Tektronix 545B which had the timebase sawtooth conveniently available on a front panel terminal).
The other scope, which displayed the picture, was connected as follows: Video to the external trig input, and also the Z input, with the timebase set to line frequency. So the video signal triggered the timebase (with careful setting of the controls) and at the same time varied the brightness of the trace as it swept the screen. Then the field sawtooth was just applied to the Y input (inverted) so that the trace started at the top of the screen and swept down, at field rate, forming a raster. Tweaking the frequency of this sawtooth gave an unlocked, slowly rolling picture. It would have been possible to extract frame sync from the video signal, but I didn't bother. Somewhere I have a photo of the picture, taken with a proper Polaroid scope camera. |
26th Nov 2022, 5:20 pm | #16 |
Heptode
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Re: Circuit to display video on analogue scope?
I also remember playing around with this, probably in 1963/4. We only had a fairly low-cost Telequipment 'scope, - I think it was an S32. We used it in XY mode & of course used the Z-mod for the video input.
It worked fairly well, & was somewhat of a novelty at the time. David. |
26th Nov 2022, 10:25 pm | #17 |
Nonode
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Re: Circuit to display video on analogue scope?
The Gould OS3350 was specifically designed for this additional purpose, I believe, I had both an OS3350 and it's book, both were lost in a lockup fire eight years ago! If I remember correctly the frontispiece photo in the '3350B manual showed it displaying TC "F" if I remember correctly!
Chris Williams
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It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 26th Nov 2022 at 10:31 pm. |
27th Nov 2022, 4:33 pm | #18 |
Octode
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Re: Circuit to display video on analogue scope?
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