[Premium-Rx] Frequency Divider Question

[Clemens Paul]

> Doesn't frequency dividing the output of an oscillator reduce the phase
> noise by 20logN dB?

I think so,too.
Perhaps the dividers may add some jitter which is insignificant
in this environment (noisy synthesizer).
Furthermore the stronger the phase noise of a rubidium standard as opposed to
a that of a good OCXO won't play any role regarding the performance of the radio
in crowded bands in terms of worse reciprocal mixing.
The synthesizer is MUCH more noisy than a rubidium standard.
On my IC-7800 I've measured the same reciprocal mixing for the built in OCXO
and a super clean Wenzel OCXO which has a 25dB better phase noise in 1kHz.
And I believe that the Synthesizer/DDS of the IC-7800 has considerably less
phase noise than that of a Harris 590A.

73
Clemens
DL4RAJ


----- Original Message ----- 
From: "Ian Wilson" <ianmwilson73 at gmail.com>
To: "Charles P. Steinmetz" <charles_steinmetz at lavabit.com>
Cc: <premium-rx at mailman.qth.net>
Sent: Monday, October 31, 2011 2:58 AM
Subject: Re: [Premium-Rx] Frequency Divider Question


> 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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>>
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