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Baird 240 Line Operation

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peterscott
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Starting from this thread http://www.vintage-radio.net/forum/showthread.php?t=130716&highlight=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/showthread.php?t=9229&highlight=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

Test-Card-4-Medium.jpgP1050517-Medium.JPG

 

www.nostalgiatech.co.uk

 
Posted : 19/05/2017 10:09 am
peterscott
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I've added another page to my website detailing the 240 line generation and showing both 405 and 240 line representations of Test Card C.

(Yes, I know Test Card C wasn't around in 1936 but it gives a better comparison than earlier test cards.)

Peter

www.nostalgiatech.co.uk

 
Posted : 31/07/2017 3:54 pm
PYE625
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peterscott said
detailing the 240 line generation and showing both 405 and 240 line representations of Test Card C.

The difference is very similar to 625/405 on a large screen set.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 31/07/2017 5:41 pm
Marc
 Marc
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Thanks for the latest update Peter, very impressive and I wouldn't mind giving it a go with the workshop PC once I get a suitable graphics card although only in 405, I don't think i'll ever be lucky enough to get a 240 line set. I feel an autumn project coming on. smile 

Marc. 

Marc
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Posted : 31/07/2017 5:45 pm
peterscott
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Hi Marc,

Suitable graphics cards are very cheap but I've added a little note to the web page warning against Nvidia cards that won't work with Win 7.

Peter

www.nostalgiatech.co.uk

 
Posted : 31/07/2017 7:43 pm
peterscott
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PYE625 said

peterscott said
detailing the 240 line generation and showing both 405 and 240 line representations of Test Card C.

The difference is very similar to 625/405 on a large screen set.  

Hi Andrew,

Very true, even to the ease of higher horizontal definition in the lower line rate.

Peter

www.nostalgiatech.co.uk

 
Posted : 31/07/2017 7:48 pm
peterscott
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The graphics card syncs do differ in two respects from the EMI 405 line standard and this can cause rather critical line frequency adjustment or hooking at the top of the picture in older sets that don't have flywheel sync. Sorting this is work in progress. The existing composite sync is simply generated by exclusive OR of the line and frame pulses but the resulting inverted line pulses within the frame sync are slightly delayed relative to their correct positions. There is also no half line pulse stream. The latter is not essential and a simple monostable circuit can correct the pulse positions. See Here. To use this circuit the Modelines need to be changed such that the Composite Sync box should be unticked and the +hsync references should become -hsync.

Peter

www.nostalgiatech.co.uk

 
Posted : 20/08/2017 10:37 am
peterscott
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I have now made a small change so that the monostables run as an injection locked oscillator to give the half line inverted pulses. The changes are that the delay of the first monostable has been halved and the output of the second monostable now also triggers the first. See here.

Peter

www.nostalgiatech.co.uk

 
Posted : 22/08/2017 12:44 pm
peterscott
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peterscott
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I initially used rather non-standard 405 frame synchronisation pulses but have now brought these into line with the standards. 

See:  https://tinyurl.com/y78c8wc8

Peter

www.nostalgiatech.co.uk

 
Posted : 28/03/2018 5:28 pm
crustytv
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Hi Peter, the results looking at the tiny thumbnail, appear to be stunning, though its very hard to tell as you have to be a member to view any photo on that forum and many may not wish join up just for that.

Perhaps you might consider loading your latest photo's in this thread? There's no restrictions on public viewing of images here which means a wider audience can enjoy your work to its fullest, as no need to join to view. If you prefer not to I completely understand, then perhaps you might consider a link to the full size example photos via your website?  ? 

Warm regards
Chris

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Posted : 05/04/2018 8:27 am
peterscott
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Hi Chris,

Sorry about the thumbnails. My little Sony 9-90 doesn't manage the 3MHz bars very well and doesn't have good DC restoration but here are the two photos. I'll also post a detail from my old HMV901 that does reproduce 3MHz and has DC. The image is direct from the screen rather than via my slightly iffy mirror.

Peter

Graphics P1050775 (Medium)
P1070188
P1070189

www.nostalgiatech.co.uk

 
Posted : 05/04/2018 9:00 am
crustytv
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Hi Peter,

Firstly no need to apologise  ? 

Secondly, WOW! the results are as amazing as I thought and to think its via an old PC card!

Thanks for posting the attachments, its also good to see your HMV 901 is still giving a great account of itself. It never ceases to amaze me just how good a picture pre-war sets give, and I have to pinch myself "pre-war". I tip my virtual hat to those guys who were pushing the leading edge of the technology back then.

CrustyTV Television Shop: Take a virtual tour
Crusty's TV/VCR Collection: View my collection
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Crusty's 70s Lounge: Take a peek

 
Posted : 05/04/2018 9:05 am
peterscott
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Chris,

Thanks for your kind words. The graphics card signal generation really is very good and gives better resolution than any standards convertor that I've seen. The only down side is that starting it up requires you (well me anyway) to drag the image or video content from your PC screen into the television screen and then select full screen before you settle down to watch anything.

I totally agree with you regarding the Marconi-EMI team.

Kind regards,

Peter

www.nostalgiatech.co.uk

 
Posted : 05/04/2018 9:21 am
peterscott
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Here the graphics card is generating the video signal via a modulator that is feeding the aerial socket of a Sony 9-90. The Sony has next to no dc restoration hence that black bars to left and right of bright areas. The sweeping diagonal band is just an aliasing effect from the camera and is not visible when viewing the set directly.

Peter

www.nostalgiatech.co.uk

 
Posted : 06/04/2018 11:37 pm
PYE625, PYE625 and PYE625 reacted
crustytv
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Hi Peter,

thanks for the video, that's absolutely brilliant and even further demonstrates just how good a results this project has yielded. Besides your initial goal of 240-line operation, If anyone is finding it difficult to justify the purchase of an Aurora, this does at least give them a cheaper introduction to also obtain 405-line standards conversion. 

 

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Posted : 07/04/2018 7:48 am
peterscott
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Running videos on your 405 line (or 240 or 625 line) sets is really easy. For example using VLC player you simply need to paste the address of any YouTube that you want to watch into the VLC Network Steaming address line and hit return.

youtube

www.nostalgiatech.co.uk

 
Posted : 07/04/2018 10:13 am
peterscott
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I can't capture the flicker on 240 line / 25 Hz using video and YouTube but I have got a very similar effect using an animated gif.  It doesn't work well with 60Hz monitor display rate but if you can change to 75Hz it compares well with the actual flicker on my HMV901. Scroll down on HERE

Peter

www.nostalgiatech.co.uk

 
Posted : 01/06/2018 7:29 pm
Jac Janssen
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Hello Peter,

For me it does not work unfortunately.
Perhaps my video card (on the mobo) is not good with 50Hz (normal use is 60Hz).

Jac

 
Posted : 06/06/2018 6:10 am
peterscott
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Hello Jac,

Yes, it just looks scrappy with 60Hz display rate. With 75Hz I find it takes a few seconds for the PC to settle down but after that I really would not be able to tell the difference between the actual 25Hz flicker on my HMV901 running 240 lines and the image on the PC monitor.

Peter

www.nostalgiatech.co.uk

 
Posted : 06/06/2018 10:18 am
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