SI570 as clock for Johnson counter – the problem

Sometimes you think you know something is wrong, but until you see what it is, you can’t really be sure.

digital_clockA quick glimpse over commonly available schematics for direct conversion radios that use SI570 and 7474 as Johnson counter (2bit quadrature generator) reveals the tip of how many things are wrong about this idea. But as those radios work in practice, I for one never bothered to look at the real life picture, which is this:

SCR0003And the resulting jerky clock is this:

si_clockAnd understandably, the final quadrature clock be as ugly as this:

quad_clockWhich is more or less, the fundamental modulated by its harmonics 🙁

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