[time-nuts] Good Phase-noise?

[Dr Bruce Griffiths]

Larry Gadallah wrote:
> 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,