Thursday, 15 August 2013

DIY video pattern generator

For future ATV experiments I was looking for a (simple) video pattern generator (PAL format), The internet learned me that there are several (expensive) special purpose ic's for this function. Also PIC-based projects are available. The search brought me also to this circuit:

This must be one of the simplest video pattern generators one can realize. It provides a black/white bar pattern. The circuit is designed around a 1$  4060. This is a 14 bit counter. 
A steps shaped block wave is created by adding the 3 output signals (contacts 4, 5 and 7) in the proper proportions.
The output signal can be adjusted to the required 1 Volt peak-peak. Contact 4 (Q5) provides a f:64 signal. When the Xtal is choosen as 1 MHz, output Q5 delivers a 15,625 Hz signal. This is what is required for the 64 us synchronization pulse (0 V).
I did trials with various Xtal frequencies and 4.43.. MHz provide three main bars each consisting of 8 subbars. I presented this signal to a small QRP ATV 1.2 GHz transmitter and when received by an analogue satellite tuner, the picture above was seen on my TV.

The circuit was realized according to the " dead-bug " rules:

If you know how a simpler video generator can be made than presented here, I am very interested.

Typical PAL video signal providing a bar pattern:

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