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, [email protected]<[email protected]> wrote:
From: [email protected]<[email protected]>
Subject: [time-nuts] oscillator choice question
To: [email protected]
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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