[time-nuts] oscillator choice question

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat May 1 21:44:44 UTC 2010


If there is no electronic tuning available one can use a DDS based 
synthesiser to produce a corrected output frequency.
However close in spurs will be problematic unless one use a couple of 
simple mix and divide stages or resorts to a Diophantine synthesiser 
using phase noise truncation spur free output frequencies from the DDS 
chip(s).

Alternatively if one implements the DDS in an FPGA its possible to 
virtually eliminate such spurs using a modified algorithm.
However this requires an external DAC to produce the required output.

Bruce

Robert Atkinson wrote:
> Hi Chris,The Racal high stability units usually use the 9420 series OCXO's. These are good oscillators but do not have electronic tuning as standard. 'they are also normally 5MHz. What is the best oscillaor depends on your requirements. The two main parameters are phase noise and hold-over performance. Hold over is how much the oscillator will drift if the GPS loses signal.
> Robert G8RPI.  
>
> --- On Sat, 1/5/10, chris at yipyap.com<chris at yipyap.com>  wrote:
>
> From: chris at yipyap.com<chris at yipyap.com>
> Subject: [time-nuts] oscillator choice question
> To: time-nuts at febo.com
> Date: Saturday, 1 May, 2010, 20:28
>
>
> I'd like to build a GPS disciplined frequency standard.
>
> I am slowly gathering up pieces.
>
> I have a Trimble Resolution T GPS card that appears to work,
> and an antenna for it.
>
> I'm thinking now of the oscillator part.
>
> I have two Racal 1992 counters with the stable oscillator option (probably 04E since these are former military units).  I also have an old Schomandl  ND-100M Frequenzdecade signal source with an  (I assume) ovenized oscillator w/unknown properties.
>
> I'm wondering if I could use an oscillator from one of these
> gizmos instead of shelling out real money on ebay?  Speaking of
> which, it seems like half the people in China are selling oscillators.
> I assume some of them are good for this application and some not
> so good?  The usual suspects from HP and Agilent are there, and
> they seem to command a pretty good (high) price.  Which is why
> I'm eyeing the Schomandl.
>
> Chris
> w0ep
>
>
>
>
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