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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > 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.... > > Matt > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.