[Premium-Rx] Frequency Divider Question

[Ian Wilson]

Doesn't frequency dividing the output of an oscillator reduce the phase
noise by 20logN dB?
Or am I missing something here.

73, ian K3IMW

On Sun, Oct 30, 2011 at 6:51 PM, Charles P. Steinmetz <
charles_steinmetz at lavabit.com> wrote:

> Keith wrote:
>
> >I am somewhat irritated by the warm up drift of my military Harris 590A,
> >(R-2368) while the crystal oven comes up to temperature.
> >As a non-invasive solution I would like to use an external rubidium
> >frequency standard, but, the one I have here is 10 MHZ
> >
> >Question...does anyone know of a (cheap and/or easy) programmable
> frequency
> >divider that could do the job? (or a fixed 10:1 divider would do too).
> >Suggestions welcomed.
>
> Here is one:
>
> http://www.perdrix.co.uk/FrequencyDivider/index.html
>
> I believe he sells completed boards (no enclosure).  He may sell
> kits, too.  There is also complete information to build it yourself,
> including PC board artwork, if you want to do that.  You could also
> cobble up a 74HC-series decade counter with some parallel output
> buffers on a scrap of copper clad and power it with a discarded wall
> wart.  You can let the gates do the input conversion to logic levels,
> but I always use a PNP diff pair to do the conversion because it has
> much less jitter and protects the logic from the bad, bad world past
> the input jack.
>
> However:  Note that the phase noise of a rubidium standard is
> substantially higher than the quartz oven oscillator in the 590A, and
> the divider will add some more, so the performance of the radio in
> crowded bands will suffer somewhat.  Personally, I would not take
> that tradeoff.
>
> I just turn mine on ten minutes before I want to use it.  If I needed
> a quicker launch, I'd either just leave it on or hack in and add
> standby power for the oven.  (I, too, am surprised that Harris did
> not power the oven continuously, or at least make it switchable so
> the customer could decide.)
>
> Best regards,
>
> Charles
>
>
>
>
>
>
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