[time-nuts] 10MHz to 32MHz?

John Miles jmiles at pop.net
Sun Apr 22 15:57:16 EDT 2007

I thought about suggesting a PLL, since a couple of 74HC counters and a
74HCT4046 could do the job for less than $20 in parts.  But I think a
separate VCO would be needed.  It doesn't seem safe to assume that the rig's
crystal oscillator either has a varactor, or is sufficiently steerable via
its Vcc line.

The other problem is that unless you have near-superhuman analysis skills,
your PLL will NOT work optimally without actually measuring and tweaking it,
or at least modelling it in a good simulator.  I don't know of any freeware
simulators for the '4046 or any other PLL chips that can be used without a
microcontroller.  You could use a microcontroller and a newer chip like the
ADF4002, which is a truly-excellent part... but in my experience, even the
nicer packages like ADISimPLL deviate from reality when the VCO gain doesn't
fall within a fairly-narrow range of popular values.  (I suspect they have a
bug, actually, but haven't had time to prove or disprove it.)

And of course, if you're going to use a microcontroller to run your PLL
chip, you might as well use a DDS.  Honestly, I'd just rig up some dividers
and mixers, borrow some time on an SA to tune it all up, and call it a day.

-- john, KE5FX

> Good day,
> *********** REPLY SEPARATOR  ***********
> On 22-Apr-07 at 21:11 Lester Veenstra M0YCM K1YCM wrote:
> >And if the 32 mhz source is a sealed unit, I suspect you will find that
> >once
> >you mechanically set it as close as practical, that varying the Vcc will
> >allow you to use it as a narrow VCO.

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