[time-nuts] I'm all of a dither.

Joe McElvenney ximac at btinternet.com
Mon Sep 21 18:17:18 UTC 2009


A fellow amateur and I have just put together the GPS-based frequency
reference published in the "Every day Practical Electronics" issue of
April/May 2009 and are both experiencing the same problem. The type-3
phase comparator of the 74HC4046 has both 1-pps and 50kHz DC-coupled
inputs designed to produce an error pulse due to the difference between
their leading edges. However, the longer pulse dominates the output
because it holds the latch in thrall despite the 50kHz pulse trying to
grab a little of the action.

My question is then, are there variants of the 74HC4046 that have a
type-3 detector which is edge-drive only? Natch, I can AC-couple and
clamp them but I just wondered. I know that in the past that there have
been differing versions of the old CD4046 and now, of course, there are
also the '7046 and '9046 types around.

Cheers - Joe G3LLV

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