[time-nuts] Question on HP5359 Time Synthesizer
bruce.griffiths at xtra.co.nz
Mon Jun 23 04:29:06 EDT 2008
Ulrich Bangert wrote:
> 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
> Ortholzer Weg 1
> 27243 Gross Ippener
> While I am writing this the drift rate has reduced to abt 1 HZ / sec.
For a ~1MHz output the contribution of the interpolator to the period is
Thus drift of around 1% (~100ps) of the interpolator range (~10ns) would
lead to a frequency drift of around 200Hz.
A trigger rate of around 1MHz is getting perilously close to the ~
1.5MHz VCO phase lock loop comparison frequency, so the VCOs may be
operating in digital hold mode.
In this mode the VCO control voltages are measured when the VCOs are
untriggered and locked and then an 8 bit DAC is used to set the VCO
control voltage when the VCO's are triggered at a high rate. In this
mode it doesn't take much warmup drift to account for what you are seeing.
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