Hello Bob: Many thanks for your kindly and detailed explanation, I think I am completely get it. I have few minicircuit SBL-1 mixer module, but I lacks a limiter circuit, I deicide to do some test near times. If I have any progress I will be glad to tell you in this mail list. By use "DMTD" keyword, I got many useful infomation of this method, when I finish original single mixer circuit, I want try "DMTD" method late times. All of these two method is interesting. Thanks again for your help!
Hui At 2012-07-27 00:55:56,"Bob Camp" <li...@rtty.us> wrote: >Hi > >Quick summary: > >Computing / period counters give you a constant number of digits of >resolution regardless of input frequency. Back when this stuff was developed >a counter that gave you nine digits a second was pretty common. > >Typical setup: > >1) Take two oscillators and tune them 1 to 10 Hz apart. The technique only >works if at least one of the oscillators can be tuned. > >2) Run the oscillators into a double balanced mixer. Normally levels near >the maximum are used on both inputs. > >3) Low pass filter the output. You want to keep the RF out of the 1 to 10 Hz >beat note. Various terminations seem to help the sensitivity of various >mixers (high impedance at audio, reactive termination at RF etc). > >4) Run the audio beat note into a limiter. The design of the limiter can be >fairly simple or quite elaborate. You need the limiter because the counters >input channels rarely do well with audio sine waves. > >5) Count the frequency of the audio on your counter. > >If you start off with 10 MHz and set them 1 Hz apart, you get a 1x10^7 >"amplification" of the frequency error. If you count that to nine digits, >the resulting resolution would be 1x10^-15. > >Of course resolution and accuracy are not the same thing. Measurement noise >will dominate the readings past a certain point. A typical setup should get >you below 1x10^-11 at one second without a lot of effort. A good setup can >get you to 5x10^-13 at one second with common parts. A fancy setup with a >complex limiter can go below 1x10^-13 at one second. > >Yes indeed there's a bit more than that to it, but that should get you >started. > >Bob > >-----Original Message----- >From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On >Behalf Of Hui Zhang >Sent: Thursday, July 26, 2012 10:44 AM >To: time-nuts@febo.com >Subject: [time-nuts] About heterodyne method? > >Hello everyone: > > I hnow 'heterodyne method' is very useful method of pricision frequency >measurement (use DBM and LPF), but I only found very few infomation when I >searched in early docments, Can someone give me more information about this >'heterodyne method'? The block diagram is best. I will very appreciate of >that. > > >Hui >_______________________________________________ >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.