[time-nuts] Question on HP5359 Time Synthesizer

Greg Burnett gbusg at comcast.net
Mon Jun 23 04:56:12 EDT 2008


Ulrich,

Your HP 5359A observations are normal, and many other HP 5359A users have 
asked exactly the same question, down through all these years since the box 
was first introduced. The main point is that the HP 5359A's purpose is 
*only* to generate precise timing. The box wasn't intended to generate 
precise frequency because, in its 'frequency mode' it only generates 
*approximate* rates by "kicking (triggering) itself in the pants" 
repetitively. (Therefore it is *not* a frequency synthesizer and its 
"frequency" is not phase-locked to its timebase.)

Interesting note: Despite fact that the HP 5359A is not designed to 
synthesize nor lock its "frequency" to its timebase, if you set its 
frequency for "10 MHz" it sometimes might actually synchronize itself to its 
10811A timebase. This interesting effect only occurs at 10 MHz and 
apparently is a sympathetic synchronization effect due to ground loop and 
proximity coupling between circuitry and the timebase 10 MHz signal. ...This 
is a very weak effect, is not by design, and, again, can only occur for 
frequency settings of exactly 10 MHz.

Cheers,
Greg

-----------------------------------

Ulrich wrote:

Gentlemen,

some time ago I had the possibility to buy a surplus HP5359 Time
Synthesizer. As far as I can judge from my measurements with a HP5370
and a SR620 the two delays that are generated inside the box with high
precision are ok and completely within the specs, which is the most
important feature for me.

There is however one annoying fact: If I use the instrument in
"frequency" or "period" mode, where the negative slope of the second
delay generator is used to trigger the first delay generator in order to
generate a repetitive waveform, I notice that a few moments after I have
pressed the "calibration" button (which should adjust everything
automatically) the frequency of the repetitive waveform will change and
drift by an amount of some 100 Hz up to a few kHz so that my counter may
read 996 kHz after a few minutes with the drift getting smaller over
time as the device warms up.

I have first thought that this effect is due to a defective 10811 in the
box but the effect is the same with an externally supplied standard
frequency. Well, the thing is: If one reads the manual carefully he will
find out that there is no spec about frequency stability to be found
anwhere in it! On the other hand the manual says to check the "trigger
assembly" in case of coarse "overall timing errors". The trigger
assembly is the point where the negative slope of the second delay
generator is feed back into the trigger circuit to make the waveform
repetitive. Am I complaining at something completely Ok or should I have
a deeper look to the trigger circuits? Hopefully one of you 5370 adepts
can give some explanation.

Ulrich Bangert
www.ulrich-bangert.de
Ortholzer Weg 1
27243 Gross Ippener

P.S.

While I am writing this the drift rate has reduced to abt 1 HZ / sec.






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