[time-nuts] comparing two clocks

Volker Esper ailer2 at t-online.de
Sat Feb 22 21:48:22 EST 2014


...and I did it in a similar way, but plottet the ADEV. See plots enclosed:
Plot 1 is Allan Deviation of 0 delay (two cables of 50cm each)
Plot 2 is ADEV of 8 meters coax cable compared to the 50cm cable.

You'll find the ADEV of the long line slightly worse, particularly at
short times.

I would recommend not to use a cable delay line longer than necessary.

Volker


Am 23.02.2014 02:49, schrieb SAIDJACK at aol.com:
> Jim,
>  
> when I did the test on the 53132A, I did the test with the two signals on  
> top of each other with a very small cable offset of 400ps, then I added a 
> 10ns  delay line to the B signal just to see if the counter would behave 
> differently.  Here are the results, pretty much looks identical with 0.4ns offset 
> or 10ns  offset.
>  
> bye,
> Said
>  
>  
>  
>  
> In a message dated 2/22/2014 10:06:30 Pacific Standard Time,  
> ailer2 at t-online.de writes:
>
> Jim,
>
> If I get you right, you want to compare the 10MHz  outputs (not the
> 1PPS). As Jim and Bob told us so far, the thing is to  provide, that
> input A _always_ starts before input B (or the other way  around).
>
> Connect the signals to an oscilloscope, and check, how much  the phase
> differs - if the rising slopes occur close together, put  some
> meters/yards of coaxial cable into one of the two signal paths. 1  meter
> is roughly worth 5ns - while the period of 10MHz is 100ns, 1m cable  will
> phase shift about 18 degrees. I didn't verify, if the coax cable  (with
> it's microphonic effect) affects the ADEV - does anybody have  experience
> with this? Otherwise I'd have to fire up my counter and have  a
> measurement on the run...
>
> Of course, inverting one signal will do  as well. If you do it with extra
> electronics that definitely will affect  the ADEV. I find it much easier
> to use some meters of cable.
>
> Ok, my  counter is heating up by now...
>
> Volker
>
>
> Am 22.02.2014 14:17,  schrieb Jimmy Burrell:
>> I need some help with a 'noob' question  regarding some practical 
> examples in some of the NIST literature. When  attempting to compare two clocks, 
> I'm a bit confused on the subject of exactly  how to use my counter to compare 
> a delayed clock relative to another. Or  perhaps I should just say 
> 'comparing two clocks'. Let's take some concrete  examples. 
>> Let's say I want to characterize my Morion MV89  ocxo using my HP5335a. 
> Obviously, I can tune the MV89's 10MHz by +/- 1Hz and  feed it to the 
> counter's input 'A'. Obviously, I can feed in a second,  external reference clock 
> at 10MHz into input 'B'.  Suppose, however, I  didn't have an external 
> reference clock. Can I compare against the counter's  internal time base by 
> hooking a line from the rear jack time base output to  channel 'B' input? Or am I 
> making it too complicated? Do I simply plug into  input 'A' and go?
>> In a somewhat related question, in this  article  
> (http://www.wriley.com/Examples%20of%201%20PPS%20Clock%20Measuring%20Systems.pdf)  where two 
> clocks, both divided to 1PPS, were compared, W.Riley makes the  following 
> statement, "The two 1 PPS outputs were connected to a Racal Dana  1992 time internal 
> counter having 1 nanosecond resolution, and the start and  stop signals 
> were separated sufficiently in time for the counter to function  properly".  I 
> wonder what exactly is meant by "separated sufficiently in  time for the 
> counter to function properly" and how one would go about doing  this? For 
> example, is inverting one of the signals sufficient separation? If  not, how is 
> this typically done? Delay line?
>> Thank  you,
>>
>> Jim...
>> N5SPE
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