Video Processor (Frame store)

Background

Milton keynes is currently served by three amateur TV repeaters; GB3TV (Dunstable), GB3MV (Northampton) and GB3TG (Milton Keynes).

Unfortunately none of these sites provide adequate coverage for most of Milton Keynes; by it's location you would assume that GB3TG should, but this is a 10GHz repeater, so line of site only. Milton Keynes is built on several hills, the signal from GB3TG becomes blocked to all but a few amateurs.

There is therefore a need for a repeater within the Milton Keynes area, where this should be hasn't been decided, some of the repeater technical requirements though have been determined.

This video processor unit has been born out of the requirement for a frame store and sync. processor unit (replacement of old sync. with new).

Processor Description

All processing is carried out within a digital system consisting of the following blocks:

• Video decoder (A/D and chroma decoders) * 2.

• Controller IC with video encoder (D/A convertor).

• Video memory.

A few of the functions enabled by this design are:

• Frame store topology - allows freeze frame and "trick" modes such as zoom, * 2 and mirror image.

• Picture in picture or quad screen (4 pictures on screen at once).

• Two input video channels each with four separate inputs.
  

• Input channels have a video clamp, effective AGC, comb filters and picture enlargement and reduction in X and Y axis.

• On screen graphics synced to output video with provision to fade in/out with fully configurable fonts and choice of 4 colours from 24 million! Graphics don't jitter about on noisy inputs.

• Colour bar generator for test use.

Picture Gallery

Explanation of pictures (click for large view)

Top
Left - P4 input signal, Middle - same signal on output showing "new" sync, Right - locked colour on P1/2 picture

Centre
Left - P2/3 picture, Middle - same picture with noise reduction, Right - caption locked to P1 picture

Bottom
Left - P4 picture with B.Level coring, Middle - same with noise reduction, Right - Mirror image

Major components used

Video decoders from Techwell type TW9901
Main quad processor from Averlogic AL700C

All major semiconductors are available from 2001 Electronics in one off quantities, crystals were purchased from Golledge.

Schematic is available here.

This is shown for information only, not many amateurs are capable of soldering in 204 pin chips (me included!). I will assist anybody that requres further information.

Note - All pictures grabbed on the output of video processor, the PC video card doesn't like poor sync!

Updated 10-11-03 S. Drury