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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Sep 21 21:17:09 UTC 2009

Joe McElvenney wrote:
> Hi,
> 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

That looks to be an exact copy of the crude GPS reference published in
Silicon Chip in March 2007 and April 2007 with corrections (synchronous
frequency divider chips were cascaded incorrectly ) in the May 2007 issue.

March 2007:
April 2007:
May 2007:

The question is did they include the corrections or not?


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