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Alternative Sources of 405 line and 240 line

A number of people have developed the use of PC graphics cards for presenting 405 line and 240 line signals to old televisions. Below is a description of the method I have used.

 I would like to acknowledge and thank some of those whose work has made this possible: Jeroni Paul for his PC application for graphics card control and for his very helpful assistance with the specifics, Kat Manton for conceiving the method, Jim Beacon for demonstrating the feasibility and Graham Rabstaff for demonstrating it from a PC.

The scheme I have been using is simply a development of that devised by Graham Rabstaff. My methods differ regarding the sync pulse generation and also in the application of sources. The present scheme works well but doesn't generate the correct sync pulse stream in accordance with either the EMI 405 line standard nor the 240 line standard of the Baird system. The Baird system did not specify any line sync pulses during the frame pulse and receivers needed a method of maintaining correct line frequency in the absence of sync pulses. In the case of the EMI sets some additional circuitry and a valve (V8) were required to be switched in for 240 line operation. The graphics card source does continue to generate line sync pulses during the frame sync pulse so there is no need for the additional V8 circuitry.

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.  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. A simple monostable circuit can correct the pulse positions and include the half line pulses. 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.

Hardware Requirements

A graphics card with two VGA outputs.

In practice this generally involves a card with a DMS-59 connector and splitter cable giving the DMS to 2 x VGA connectors.

One VGA output will support the PC whilst the other will connect to your television via a small VGA to composite video adaptor and a modulator to present the signal at the aerial socket. The adaptor can be as simple as the circuit shown in Jeroni Paul's notes:

Various modulator circuits are available I am using the design from Darius' standards convertor

The sound signal is simply taken directly from the PC speaker output to the input of the sound modulator.

A PC with a PCIe x16 motherboard slot.

Software Requirements

Jeroni Paul's Modeline Editor

VLC Player for Windows

After downloading the Modeline Editor you will need to sign in to your PC as administrator and have ability to edit the registry.

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 to 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.

Static images can also be displayed and for that I use Irfanview.

An aspect ratio change is also required here and the resulting images can be seen displayed on the 1937 HMV901 below:

The 405 line Test Card C:

The 240 line Test Card C:

This gives better resolution of the finest bars because the video bandwidth is less demanding but the fewer lines and lack of interlaced scanning is apparent.

Looking at a photograph of a 240 line Baird image it appears to compare quite favourably with the 405 line EMI images but what you are not seeing in the still photograph is the very noticeable flicker from the Baird 25 Hz frame rate.