[time-nuts] Good Phase-noise?

[Larry Gadallah]

On 2/28/07, time-nuts-request at febo.com <time-nuts-request at febo.com> wrote:
> Message: 6
> Date: Thu, 01 Mar 2007 12:05:38 +1300
> From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
> Subject: Re: [time-nuts] Good Phase-noise?
> To: Discussion of precise time and frequency measurement
>         <time-nuts at febo.com>
> Message-ID: <45E60AC2.4070700 at xtra.co.nz>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Larry Gadallah wrote:
> > Hello all:
> >
> > I considering a do-it-yourself GPSDO, and I started by looking for a
> > good OCXO. I have been given a quote for a unit with the following
> > phase-noise numbers:
> >
> > -120 dBc/Hz at 10 Hz
> > -145 dBc/Hz at 100 Hz
> > -155 dBc/Hz at 1 kHz
> > -160 dBc/Hz at 10 KHz
> > -160 dBc/Hz at 100 KHz
> >
> > My question is this: Are these good specs? They look pretty good to
> > me, quite comparable to the HP 10811 numbers.
> >
> > Thanks,
> >
> Larry
>
> Whilst these phase noise figures are around 20dB or so worse than the
> state of the art, they are adequate.
> The short term frequency stability is determined more by the OCXO's
> Allan variance as a function of averaging time.
> In particular the Allan variance for averaging times from 1 sec to 1000
> sec or more is significnt.
>
> Bruce

Hello Bruce:

Thanks for your comments. I should have mentioned that these numbers
were from a COTS OCXO, and that it is priced in the $200 range.
Ignoring the price, can you obtain 20 dB better performance from a
COTS device? Is it better to simply look for a good HP 10811 (in this
price range)?

I understand the issue of Allan deviation versus frequency stability,
but my main purpose for this oscillator is as a local oscillator
reference for radios, where increased phase noise quickly causes the
receiver performance to degrade.

Cheers,
-- 
Larry Gadallah, VE6VQ/W7                         lgadallah AT gmail DOT com
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