[time-nuts] looking for SMT oscillator SC cut, with no oven

[Mike Garvey]

You might start with Leeson's equation to calculate the resonator Q that you
need to get the phase noise you desire.  Overtone resonators have higher Q,
but they are too "stiff" to keep on frequency (with a reactive tuning
network) under conditions in which the resonator is exposed to any practical
range of (ambient) temperatures.  Said another way, to get the phase noise
you desire, you may need a Q that can only be achieved with an overtone
resonator that cannot be brought/kept on frequency except by keeping its
temperature stable (which needs to be above any expected ambient).

There is a lot of good material on this topic at
http://www.ieee-uffc.org/publications/books/index.asp 

If you can afford the complexity and power of synthesizing the desired
frequency (with a DDS, perhaps) from the overtone resonator you could absorb
the resonator inaccuracy with tuning commands that you send to the DDS.

Mike

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Jim Lux
Sent: Wednesday, August 26, 2015 2:24 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] looking for SMT oscillator SC cut, with no oven

For a project at work, I'm looking for a good close in phase noise
oscillator (better than -100dBc@ 10Hz, -120dBc would be nice) at 100 MHz in
a SMT form factor.  But it doesn't need good temperature stability. 
There's tons of SMT OCXOs out there with reasonably good performance, but
they draw "watts".  My application is actually quite temperature stable
already AND I have an external reference to measure against.

Most of the lower powered oscillator modules are TCXO, and have, maybe,
-80dBc at 10MHz.

I guess we could go to a discrete design with a crystal and amplifier, but a
little clock module would be a simpler solution.





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