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Old 19th May 2017, 8:56 am   #1
peter_scott
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Default Baird 240 line Operation

Starting from this thread http://www.vintage-radio.net/forum/s...hlight=foth+tv

I thought I'd see if I could get 240 line operation working with a similar graphics card. I initially tried using an nvidia 290 with my Win 7 64 bit PC but no joy. An email to Jeroni Paul the author of the Modeline Editor let me know that the nvidia is not compatible with Win 7 but he explained that the ATI cards are. I then bought an ATI HD2400XT and tried loading the modeline from Kat Manton and Jim Beacon http://www.vintage-radio.net/forum/s...light=240+line

This resulted in a 50Hz 520 line output. I struggled with this for a bit and contacted Jeroni Paul again. He was very helpful and suggested that the very low pixel clock rate could be the problem and he also offered two alternative modeline suggestions:


"If the problem is low pixel clock it is easy to increase, try these:
Modeline "1120x220_25 6,0kHz 25,0Hz" 7.488 1120 1136 1168 1248 220 221 233 240 -hsync -vsync
Modeline "1680x220_25 6,0kHz 25,0Hz" 11.232 1680 1704 1752 1872 220 221 233 240 -hsync -vsync"

The first didn't work and the second gave an image with only about a quarter of the line width filled but it dawned on me that in trying to display 405 lines with RAMBO1152's scheme I had to adjust the aspect ratio of the source material, increasing its width by 20%

In the 240 line case the aspect ratio change needs to be more dramatic and you can see the source and the 240 line 25 Hz image on my HMV901 below. (Yes, it does have an annoying flicker.)

The picture is far from perfect but the old set is doing quite well given that the H and V syncs are just combined by crude voltage addition and it doesn't have the V8 triode fitted in the line timebase.

Very many thanks to all those who whose work has helped me get a result.

Oops! I should also add thanks to Darius whose modulator circuit I used.

Peter
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Old 19th May 2017, 9:16 am   #2
Lloyd 1985
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Default Re: Baird 240 line Operation

Hi,
That picture looks pretty good! I was half expecting the Line structure to be more obvious.

Very interesting thread, I've still yet to try using a PC to display 405, not much point in me trying 240 lines, as I've nothing to display it on!

Regards,
Lloyd
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Old 19th May 2017, 11:33 am   #3
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Default Re: Baird 240 line Operation

Thanks Lloyd,

Yes, I was quite surprised by it but of course a 240 line Baird picture has more lines than a 405 with poor interlace and what represents 3MHz bandwidth on a 405 line set is only 1.8MHz with 240 line.

My set-up is all a bit messy just now but I'll sort out the syncs and there's a series capacitor in the video path with too small a value at present giving rise to the dark shading at the top of the picture.

The next problem is how to change the aspect ratio of video source material.

Peter

Last edited by peter_scott; 19th May 2017 at 11:39 am.
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Old 19th May 2017, 4:01 pm   #4
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Default Re: Baird 240 line Operation

What proportion of surviving 240/405 sets have both standards still working? It can't be many...
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Old 19th May 2017, 4:16 pm   #5
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Default Re: Baird 240 line Operation

There are very few and of those that still retain the V8 circuitry almost all had their standards switch removed.

My set never had the the 240 line circuitry and the V8 position has a blanking plate where the valve was fitted in early sets.

I did need to up one of the frame oscillator caps to bring 240 line within frame hold control range but there is no problem adjusting the frame hold between 405 and 240 without any switching or component changing.

I haven't changed anything in the line oscillator. I did dig out a V8 valve with the intention of piggy-backing the original circuitry but I don't think I really need it. It's quite stable as is. The frame sync needs sorted as you'll see from the displaced picture but that is just due to the simple voltage adding sync combiner and I do intend to sort that.

Peter
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Old 26th May 2017, 7:31 am   #6
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Default Re: Baird 240 line Operation

Very impressive results Peter!

I was wondering if more people have results generating 240 lines (or any other interesting standards) with a PC video card....

Jac
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Old 26th May 2017, 12:16 pm   #7
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Default Re: Baird 240 line Operation

Seeing the result, another difference that I forgot to mention but I remember Jac describing is that the Baird standard results in a dimmer picture because the frame refresh rate is half that of the EMI standard. This is quite noticeable.

Peter
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Old 26th May 2017, 12:46 pm   #8
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Default Re: Baird 240 line Operation

I don't understand why that should be. The 'trace' speed of the Baird standard is less than that of the Marconi-EMI. In 1/25 of a second, it only has had to travel 240 lines, whereas the Marconi-EMI beam has traversed 405 lines in the same period. So the beam 'lingers' longer, meaning it should be brighter.

Having said that, this sort of question can be deceptive and I could easily be wrong! Please tell me why I am.

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Old 26th May 2017, 4:11 pm   #9
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Default Re: Baird 240 line Operation

Hi Steve,

I guess it depends on two factors, the duration & beam current required to reach maximum light output and the persistence after the beam has passed.

If we assume that there is a maximum light output or saturation and that both the Baird and EMI scans reach this value then with approximately the same number of lines scanned (240 v. 202) the EMI refresh happens twice as often and if the persistence is short relative to 20 ms then the EMI will be brighter.

Perhaps Baird used longer persistence CRTs than EMI.

Peter

Last edited by peter_scott; 26th May 2017 at 4:25 pm.
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Old 26th May 2017, 4:35 pm   #10
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Default Re: Baird 240 line Operation

Interesting.

The EMI refresh happens twice as often but wouldn't it also be spread over twice as much screen, so be half as intense? So this effect, at least, might be cancelled out.

This is getting my brain out of joint (not difficult)...

Steve
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Old 26th May 2017, 5:37 pm   #11
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Default Re: Baird 240 line Operation

When you say twice as much screen is that because you are assuming the spot size is half the width of the Baird?

Switching between 240 and 405 in my set the spot size remains the same.

Yes, the EMI is not retracing over the same phosphor areas (or shouldn't be) as in the previous half frame but there is always 202 lines worth scanned every 20 ms. In Baird you do get more lines but those 240 lines have to last your eyes for 40 ms.

Peter
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Old 26th May 2017, 5:53 pm   #12
Panrock
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Default Re: Baird 240 line Operation

Quote:
Originally Posted by peter_scott View Post
When you say twice as much screen is that because you are assuming the spot size is half the width of the Baird?
No. As I imagine it there will be a glowing 'tail' of afterglow like a band of lines fading away up the screen after the phosphor has been woken up by the scanning beam.

This tail will be twice as 'fat' up the screen on the 20mS frame scan of 405 than on the the 40mS of 240. But since it is pulled out more, it will be half as intense. I purposely haven't used the word 'bright' here since that could refer to the overall light level, which (as I see it) would remain the same.

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Old 26th May 2017, 6:18 pm   #13
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Default Re: Baird 240 line Operation

Yes, the question is whether a phosphor area will be just as bright when scanned with a faster traversing beam. For my assertion of brighter EMI pictures to be true then any reduction in intensity due to scanning speed would need to be of a smaller order than the reduction due to a doubling of the time between frame scans.

All I can say is that with my CRT characteristics the Baird image is flatter (less intensity of whiteness).

Peter
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Old 4th Jun 2017, 5:31 pm   #14
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Default Re: Baird 240 line Operation

Previously in this thread I had been using the crude voltage addition for line and frame syncs. I've now tried using the composite sync generated by the graphics card and the modeline editor. The syncs are still not as per the EMI 405 standard but are an improvement regarding interlace.

Below are images of the modeline editor with the two standards and screen shots taken from the HMV901 with 405 and 240 respectively.

Peter
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Old 4th Jun 2017, 5:47 pm   #15
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Default Re: Baird 240 line Operation

Great results Peter!

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Old 4th Jun 2017, 6:18 pm   #16
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Default Re: Baird 240 line Operation

Further to the last posting Jeroni Paul the author of the modeline editor sent me an optimal modeline for 240 that remains within the pixel clock limits of my graphics card but requires a less extreme aspect ratio adjustment for the source material.

Peter
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Old 4th Jun 2017, 6:29 pm   #17
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Default Re: Baird 240 line Operation

Thanks Jac, all praise should go to Jeroni Paul.

Peter
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Old 11th Jun 2017, 11:29 am   #18
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Default Re: Baird 240 line Operation

It has taken me a bit of time to get the source material aspect ratio corrected for video playing but I've now discovered that you can set user defined playback ratios in VLC Player. There are some standard ratios offered under the "Video" tab but to get user defined you need to run VLC from the command line.

So: In Windows hit Start and type "cmd" without the quotes into the search box then hit return.

In the command window you might see:

C:\Users\User>

At the prompt type "cd .." without quotes.
to get up one level or type it again to get up to C:>

Then at the prompt type:
"C:\Program Files\VideoLAN\VLC\VLC.exe" --aspect-ratio=14:5

Exactly as above including the quotes. This will start VLC Player and when you select the video it will have the 14:5 aspect ratio needed for 240 line operation.

To display this you will need to download WinModelines from:
http://www.geocities.ws/podernixie/h...deline-en.html

and copy the modelines.
For 405:
Modeline "664x377_25 10.1kHz 50.0Hz" 8.100 664 680 702 800 377 378 395 405 interlace +hsync -vsync

For 240 / 25:
Modeline "1200x220_25 6.0kHz 25.0Hz" 8.020 1200 1217 1291 1336 220 221 233 240 +hsync -vsync

and tick the "Composite" box for VGA2.

and hit "Save Changes" The PC will reboot to incorporate the changes.

Then in Control Panel, Display select the second window select the 1200x220 for 240 line.

The VGA output from your graphics card will need to be connected to your 240 line television via an appropriate modulator (e.g. Aurora with switch 6 selected) and you can now use your PC mouse to slide the VLC player off to the right side of your PC display and into your television display. To fill the screen you need to hit f on your keyboard whilst the mouse pointer is in the VLC window on your television screen. (Esc returns from full screen mode.)

The same procedure can be used for 405 lines but only requires a 20% increase in the aspect ratio width.

Peter

Last edited by peter_scott; 11th Jun 2017 at 11:55 am.
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Old 12th Jun 2017, 8:32 pm   #19
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Default Re: Baird 240 line Operation

Quote:
Originally Posted by Panrock View Post
Quote:
Originally Posted by peter_scott View Post
When you say twice as much screen is that because you are assuming the spot size is half the width of the Baird?
No. As I imagine it there will be a glowing 'tail' of afterglow like a band of lines fading away up the screen after the phosphor has been woken up by the scanning beam.

This tail will be twice as 'fat' up the screen on the 20mS frame scan of 405 than on the the 40mS of 240. But since it is pulled out more, it will be half as intense. I purposely haven't used the word 'bright' here since that could refer to the overall light level, which (as I see it) would remain the same.

Steve
Hi Steve,

I confess that you are probably correct! When run on 240 line I changed the line rate on the receiver and seeing a compressed image in the centre of the screen I changed the aspect ratio of the source so as to fill the screen as shown in previous postings. What I hadn't spotted was that the reduced line speed also increased the scanned width so although my test card filled the screen there were black areas off to the left and right.

I now realise that I need to reduce the scanned width and distort the source even further than I had been doing to fill the scan.

Whilst switching between 405 and 240 is not an instantaneous event I think you are correct in saying that the level of intensity is similar and not less in 240 as I was detecting. Previously although my line frequency was correct the actual time spent scanning each of my 240 lines was shorter than it should be because the scanning beam also spent time scanning the off screen black areas.

The flicker is just as noticeable but the "intensity" is now correct.

Apologies and kind regards,

Peter
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Old 17th Jun 2017, 10:31 am   #20
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Default Re: Baird 240 line Operation

With a few more suggestions by Jeroni Paul the process of running 405 line or 240 line or what have you lines is now very simple.

Download the Modeline Editor for Windows here:
http://www.geocities.ws/podernixie/h...deline-en.html

Having loaded the Modelines using Jeroni Paul's editor as in the first picture below, you don't need to use the Modeline Editor from now on. If you want to switch line rates then you use your Windows Control Panel, Display, Change Display Settings then select your Number 2 display and select the resolution you require.

If you want display video material the freeware application VLC Player works very well. You do need to make a little change to the pixel aspect ratio and so I have two shortcut icons on my Windows Desktop both pointing to VLC Player.

As normally loaded the Target in the shortcut might read:
"C:\Program Files\VideoLAN\VLC\vlc.exe"

For my 405 line shortcut to VLC Player I changed the Target to read:
"C:\Program Files\VideoLAN\VLC\vlc.exe" --monitor-par=11:14

And for my 240 line VLC Player the Target is:
"C:\Program Files\VideoLAN\VLC\vlc.exe" --monitor-par=11:45

Now if I want to display a DVD on a 405 line receiver I connect my Number 2 VGA port on the PC to my Channel 1 modulator and click on my 405 VLC Player. I select Media, Open Disc.. then in the new window "Play" and the DVD menu comes up in the window. I then drag that window over to the right and off my PC screen and into my TV screen. Then hit f to get full screen then position the cursor over the video to play and hit return.

The Sony 9-90 has next to no dc restoration hence the dreadful picture but it looks better on less contrasty material e.g. Test Card C also displayed from the graphics card + modulator.

Peter
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Last edited by peter_scott; 17th Jun 2017 at 10:40 am.
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