Bob, > ~2x10^-10 you can do this with a good frequency counter, no > mixers needed. ~2x10^-11 you can do this with a very good > /hard to find / expensive frequency counter. 1.0x10^-11 > pretty easy, nothing very fancy required for a single mixer > approach. 1.0x10^-12 works fine with an RPD-1 and some care, > but not a lot of crazy stuff 1.0x10^-13 you need some > attention to detail, and may need a better mixer. 1.0x10^-14 > can I come live at your house? If you have this sort of > stuff, the cost of a fancier test setup should be a minor > issue. 1.0x10^-15 indeed people do measure this stuff. > Proving accuracy at this level involves a lot of work on > secondary effects.
In general I agree to all these numbers. I just want to point to the fact that a HP5370 or a SR620 allow for a kind of "high resolution mode". This is a mode in which the counter is externally armed to make 1000 TI measurements per seconds and display the mean of them. Which gives a SQRT(1000) improvement of all counter related non systematic errors. My experiments with a SR620 indicate a 6E-13 noise floor for Tau = 1s without any need for mixing for two 10 MHz sources. Naturally this works ok only for source frequencies >= 1000 Hz ( The higher the frequency the less trigger noise ). For those of us who have no access to H2-masers or BVA-oscillators as a reference this may be not exactly an overkill but quite good to characterize HP10811/FTS1000(1200) or the like not to mention anything worse than that. Best regards Ulrich > -----Ursprungliche Nachricht----- > Von: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] Im Auftrag von Bob Camp > Gesendet: Donnerstag, 19. Januar 2012 18:37 > An: 'Discussion of precise time and frequency measurement' > Betreff: Re: [time-nuts] mixers for frequency measurement > > > Hi > > It's always a "that depends" sort of thing. What do you have > to measure? If you happen to have a pair of Hydrogen Masers > in your basement, that's going to be more of a challenge than > a pair of telecom rubidiums. > > In general, the mixer is less of an issue than the circuit > you follow it up with. Squaring up a 1 Hz sine wave isn't as > easy as you might think, if you want to keep it quiet. A Mini > Circuits RPD-1 will do a pretty good job until you get to > fairly exotic measurement levels. > > A diode mixer squares up the sine wave you feed it. If you > are running in saturation, there is very little difference > between sine and square feed. Again for ultra fancy stuff, > you would want to run sine wave and drop the levels a bit. > Saturation brings in some side effects. Either way, you will > have some sensitivity to input levels. > > All of this will really only give you an answer to - how good > is this pair of gizmos right now? Coming up with an answer > that's specific to gizmo A vs gizmo B is a bit more complex. > If you have the luxury of a "perfect" reference for gizmo A, > then you can blame what ever you see on gizmo B. Even then > you can't really tell how good gizmo A is. > > So what sort of units does this all have? Sticking at one > second tau and talking about accurate data (not resolution) > on a fairly normal part: > > ~2x10^-10 you can do this with a good frequency counter, no > mixers needed. ~2x10^-11 you can do this with a very good > /hard to find / expensive frequency counter. 1.0x10^-11 > pretty easy, nothing very fancy required for a single mixer > approach. 1.0x10^-12 works fine with an RPD-1 and some care, > but not a lot of crazy stuff 1.0x10^-13 you need some > attention to detail, and may need a better mixer. 1.0x10^-14 > can I come live at your house? If you have this sort of > stuff, the cost of a fancier test setup should be a minor > issue. 1.0x10^-15 indeed people do measure this stuff. > Proving accuracy at this level involves a lot of work on > secondary effects. > > Again, that's all at one second tau. Change the tau and *all* > the numbers move. > > One other notes. If you have two equal / identical devices > and they measure 1.4x10^-11, then they both are at > 1.0x10^-11. Unless you take a lot of data, your 1.0x10^-11 > reading may only be accurate to > 10%. Getting good data at > longer tau's takes a lot of time. > > Bob > > > > -----Original Message----- > From: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] On Behalf Of Chris Albertson > Sent: Thursday, January 19, 2012 12:04 AM > To: Discussion of precise time and frequency measurement > Subject: [time-nuts] mixers for frequency measurement > > I want to get set up to make accurate frequency stability measurements > at reasonable cost. I think mixers are the way to do that. I'll set > up a single mixer first them later learn to use the double mixer > technique. But I will use the simpler single mixer to try out the > parts. My goal is a multi-channel double mixer setup. > > First question: Which type of mixers work best for this. I have > some SA612 chips in the parts bin. Or should I be using > diodes or something else. Yes I know I could simply buy one > from Mini Circuits but that defeats the purpose which is > learning how to do this > > 2nd question. if the device under test is a square wave > oscillator is it best to run the square wave right into a > mixer or filter them to sine waves first. I see pros and cons > of each. What do the experts do? > > -- > > Chris Albertson > Redondo Beach, California > > _______________________________________________ > 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. _______________________________________________ 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.