Roy Lewallen wrote in message ...
Make sure to keep the capacitor leads in the filter very short, and
build the filter so there isn't a sneak path around it. HF filters often
lose their lowpass characteristics at VHF and above due to stray
impedances and resonances. The 74HC series switches very fast, so it
generates some really high frequency stuff you really need to
effectively filter.

often, u might find a need for a diplexer at the output of the 74HC
series! quite like terminating the HEXFET power amps. I would suggest
that u include a 22 ohms resistor in series with the output and about
20-30 of capacitor to smoothen out the jitter on the square wave
edges. we used to need this to prevent the memory IC from blowing up
when driven by fast TTL chips with a large fan out.

- farhan