[time-nuts] State of the art of crystal oscillator measurements
john at miles.io
Thu Aug 11 18:47:06 EDT 2016
Right, I'm speaking specifically of L(f). The device being driven by the oscillator doesn't care about the NF of the driver stage, only what a PN analyzer would measure at the output jack.
For any 50-ohm source, the practical L(f) floor is -177 dBm/Hz - the carrier power in dBm. No oscillator with an output of 0 dBm can be quieter than -177 dBc/Hz at any offset, but an oscillator that puts out +20 dBm could approach -197 dBc/Hz.
Given a proverbial black box containing a +17 dBm oscillator that measures -195 dBc/Hz at 100 kHz, the interesting question is, "What's in the box?" There could be a passive resonator that's shaving off the broadband noise after the last active stage without contributing additive noise of its own. Another possibility might be cross-spectral collapse due to correlated thermal noise from the splitter.
-- john, KE5FX
Miles Design LLC
> -----Original Message-----
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> Subject: Re: [time-nuts] State of the art of crystal oscillator measurements
> NO, the maximum possible noise dynamic range is ( 177 + Pout) [dBm] -
> Transistor large signal NF ( dB),
> the signal to noise ration is dimensionless !!!!
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