[time-nuts] About heterodyne method?

[Hui Zhang]

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" <lists at 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-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>Behalf Of Hui Zhang
>Sent: Thursday, July 26, 2012 10:44 AM
>To: time-nuts at 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
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