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.