This post is aimed at the hobbyist electronics constructor; but others might find it useful also.

Some graphics cards have a TV output that you can connect to the UHF aerial socket of a TV set using a co-axial lead with a co-axial TV aerial plug on each end. There’s a problem with this method, in that the picture is terrible.

The graphics card takes the binary H-sync + V-sync  signal, and passes them through a UHF modulator: Result = the synchronisation pulses aren’t properly attenuated into the composite sync pulses that the TV requires, and the resultant picture becomes distorted as a result; therefore it looks a mess.

There is, however, a relatively simple circuit which uses no more than a quad-exclusive-OR gate TTL chip and a couple of transistors, plus 2 capacitors and 9 resistors; which does the job better and will interface a VGA output of a graphics card to the SCART input of a television set.

If you have the necessary constructional abilities including soft-soldering (on veroboard), then this might be a fun project to build in your spare time.

The circuit basically combines and attenuates the H-sync and V-sync outputs from the graphics-card into the composite sync pulses required by a TV set. The RGB signals are left unchanged. Unlike the TV output of a graphics card; these signals haven’t been frequency-shifted to UHF in order that they can be seen at the UHF aerial input of the TV set. This in itself removes a huge chunk of the distortion that can result from such a frequency change – Only for the TV set to change the UHF to IF and split up the signal into its constituent parts…

You’ll find all the details; circuit diagram, component layout, the lot, by clicking this link. Enjoy.