My 3458A can make measurements down to the 10nV level. At 7 1/2 digits it can do 60 readings a second. At 8 1/2 digits it slows down to 6 readings a second. The real question is the frequency of the noise. I have yet to interface it to HP-IB bus. I have several Z3801's I could try it on. Colin
Good. Thanks for the cool plots. OK, my eyeball sees: 5 uV peak-peak, maybe 2 uV rms. 10 uV peak-peak, maybe 4 uV rms. < 1 uV peak-peak, about 0.2 uV rms 4 uV peak-peak, guess 1 uV rms 3.5 uV peak-peak, < 1 uV rms 10 uV peak-peak, 1 uV rms 3 uVpp per spec This suggests that one could get Vref noise down to about 1 uV (or better if you measure rms). Does anyone on the list have actual experience with this issue? Anyway, assume a full 1 uV of noise and assume a 10811A with an EFC sensitivity of 1e-6/volt. Then Vref noise translates to 1e-12 in frequency -- which is worth considering since it's in the same ballpark as good OCXO noise. Maybe not the dominant factor, but a potential contributing factor. For example, below is a 10-minute frequency plot of a typical hp 10811A which has a low ADEV of about 2e-12 (tau 1 to 10 seconds). The scale is 1e-11 / division. http://www.leapsecond.com/museum/hp10811/log14669v.gif So you can imagine that Vref noise on the order of 1e-12 might just start being noticeable in the plot, meaning that if you want short-term performance down in the low 12's and if you have an OCXO that even gets that low, then you want to keep your Vref (and DAC, filters, etc.) clean to microvolt levels. It's just a back of the envelop calculation so I'm not really sure. Someone correct me if you see something wrong. Related - does anyone have equipment in your home/lab that can directly measure, at uV or sub-uV levels, noise on the EFC line? I wonder how clean a Z3801A EFC is, for example. Also an idea - is there an easy way to artificially increase Vref noise, by say 10x, so one could see if that change made any measurable change in OCXO output ADEV or phase noise? /tvb __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
