[time-nuts] HP 3586 entirely referenced to 10MHz: A solution II

[paul swed]

I am thinking the answer is not the interesting thread.
Its yes, that approach was considered.
I can't speak for Bert but the issue has been understood for a long time
actually. At least 10 years since my first purchase.

When I consider a problem I tend to look at the trade offs trade offs. The
ability to actually be reproduced, simple, parts availability, low cost,
stable, and a lot of other factors. Kind of would anyone else ever build
something like X.

So when FPGAs get introduced into the thread it starts to change the
complexity of the project and the likelihood of very few actually having the
ability to design or enhance and then burn the chip.

The is a heck of answer to a tough problem at a cost of $ 8 total for both
chips.

Can be improved, gets more difficult as you improve it. Like everything
else.
Regards
Paul
WB8TSL





On Mon, Apr 4, 2011 at 5:33 PM, David I. Emery <die at dieconsulting.com>wrote:

> On Mon, Apr 04, 2011 at 07:19:38AM -0400, Chuck Harris wrote:
> > Basically, the higher the division ratio in a PLL synthesizer,
> > which is what you are describing, the greater the phase noise.
>
>         No question about that, indeed.
>
>        But I am talking about a very low bandwidth loop (presumably
> well under 1 HZ should work) which means the phase noise contribution
> from the dividers and reference should be only inside that 1 Hz
> bandpass. Outside of that the original crystal oscillator phase noise
> should control, and while this won't improve that it also won't make it
> any worse.
>
> >
> > You can think of it this way: Both the reference, and the oscillator
> > being controlled, need to be divided down to some common frequency
> > that you feed to the phase detector.  The entire time the counter is
> > counting up the cycles to get you a cycle of that common frequency,
> > the oscillator is not being disciplined.   It is only after the
> > count gets done that the phase detector can compare the two signals
> > and create a correction correct for the error in the oscillator.
>
>         True, but I am pretty sure the original crystal oscillator (even
> modified with a varactor for tuning) was not phase-noisier than the rest
> of the instruments LOs.  It is, after all, a LF crystal oscillator
> running at 13 or 17 KHz with presumably a high Q crystal which shouldn't
> to the first order have unreasonable phase noise in the band around it.
> The original problem was that this oscillator was not locked to a
> reference and could drift a few tenths of a HZ (and maybe even Hz)
> randomly with temp - not that it had too much phase noise.
>
>
> >
> > The DDS is essentially a hardware solution to finding a suitable
> > divider ratio to convert one frequency into another.
>
>         I do understand DDSes.
> >
> > -Chuck Harris
>
>
> --
>  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass
> 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole -
> in
> celebration of what could have been, but wasn't and is not to be now
> either."
>
>
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