[time-nuts] State of the art of crystal oscillator measurements

John Miles 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-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of KA2WEU--
> - via time-nuts
> Sent: Thursday, August 11, 2016 2:37 PM
> To: time-nuts at febo.com
> 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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