[time-nuts] comparing two clocks

[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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