[time-nuts] Spec An for phase noise measurements
jmiles at pop.net
Wed Jan 23 19:26:04 EST 2008
Are you using a noise marker that yields dBc/Hz values? The FFT window
function has its own required noise-response correction value, so if you're
just looking at a marker and doing the log10(RBW) subtraction yourself, that
could account for the difference.
Also, if there is a noise marker, check to see if it reads dBc/Hz or dBm/Hz.
Most of them read dBm/Hz values, which are obviously only equal to
conventional dBc/Hz values if you're measuring a 0-dBm carrier.
-- john, KE5FX
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Matt Ettus
> Sent: Wednesday, January 23, 2008 4:08 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Spec An for phase noise measurements
> > I am seeing the following performance when measuring the built in 30
> > MHz reference:
> > 100 Hz -81dBc
> > 1 kHz -108 to -110
> > 10 kHz -117
> > 100 kHz -125
> > 1 MHz -131
> > All of those are 3-8dB better than the spec, except for at 1 MHz where
> > the spec is -135. The measurements do jump around a bit.
> If I change to "Digital mode for <100 Hz RBW", and turn on averaging,
> I get much better results from the analyzer --
> 100 Hz -100dBc
> 1 kHz -110
> 10kHz -120
> 100kHz -129
> 1M -135
> This, of course, makes me question all the measurements....
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