[time-nuts] FRS-C TTL / sine outboard filter question

Leigh L. Klotz, Jr. WA5ZNU Leigh at WA5ZNU.org
Wed Jun 23 20:44:37 UTC 2010

> ...
>> [snip]
> If you need a sine wave output but don't want to change anything inside,
> just add a lowpass filter.
> A 5th order LPF (three inductors/ 2 caps or vice versa) should give you
> a clean sine wave output.
> Just add a coupling cap to remove the DC component.
> Adrian
> _

Thank you, Adrian.  I'll pursue both options, internal fixes and external
filter.  A multi-pole LPF is easily understood, and I don't believe I care
about passband ripple, though I wonder a little about the effect of the
coupling on phase changes (i.e., does this have any unfortunate effect on

I still don't know if a crystal ladder filter will suppress the harmonics,
but I did get the answers that make me not need to ask anymore (1. fix the
internal filter, 2. use the high Q xtal filter for optional removal of
close-in noise)

Given time I would do all of these things, but I may not get to them all!


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