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

[David I. Emery]

On Mon, Apr 04, 2011 at 02:00:14AM -0400, David I. Emery wrote:
> On Sat, Apr 02, 2011 at 04:13:55PM -0400, Chuck Harris wrote:
> 
> > Unlike simply stabilizing the BFO crystal as you propose.
> 
> 	Has anyone given any thought to an alternative - phase locking
> the original BFO Xtals with a very narrow bandwidth loop to something
> derived from the 10 Mhz standard in such a way that the final frequency
> of the BFO comes out exact ?   Looks to me (superficially without looking
> at the schematic carefully) like this might be possible too...

	To elaborate a tiny bit, if you divide 10 MHz to 25 HZ you could
use that as the reference for a classic PLL loop that stabilized the
crystals with a varactor... provided of course suitable low pass
filtering was used.   There are also approaches involving doing early
late sampling of the BFOs on selected edges of the 10 MHz clock which
could be done more digitally in a FPGA.

	I presume one can pull the existing crystals enough with some hacking
of the oscillator to add a varactor...

	This would avoid a non integer frequency setting where the DDS
approach does not (unless you multiply by 3 to 30 MHz first I think).



-- 
  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."