Bob Camp wrote:
Hi
The 5335 is a pretty nice counter, you can use the math functions to get just about anything you want displayed. One simple example is to just subtract 10 MHz from the count and display the difference.
Indeed. The 5335 can display 12 digits but does not overflow the display
as some other counters but display the 12 most significant digits. The
math function allows you to remove the most significant digits in order
to display more digits. Good math-functions is necessary for good
counters, I regularly use them. Correctly used you may often crank out
the numbers you are interested in fairly quickly.
The problem you run into is overflow in the counter chip. Somewhere around 100 seconds you run out of storage with a 10 MHz input.
The Gate Time is specified from 100 ns to 10 Ms. I think the CPU handles
the overflow flag in the MRC and clears it.
The Gate Time can be set up to 4 seconds on the front (I really love the
directness of the Gate Adjust knob, miss that in many other counters)
and "about 1 second" using GPIB GA command. There are three ways to get
longer gate time, Manual Trigg on the front panel, External Arm input at
the back and using the GO (Gate Open) and GC (Gate Close) GPIB commands.
The single shot resolution is about 1 ns, each of the interpolators is
good for about 500 ps, but since they always combine the result is 1 ns.
While increased time-base will give increased frequency resolution, the
stability of the reference time-base becomes an issue. To measure
stability the way we like (Allan Deviation and friends) they vary with
the gate-time (which we call tau in time-nut-speech), so a counters
resolution can be expressed as resolution divided by tau as a single
figure of merit (which is an oversimplification). Another figure of
merit is the single-shot resolution, the time resolution for a single
trigger event. There is actually the hardware resolution and that which
includes trigger-jitter (which is more usefull). The SR-620 is at about
25 ps, but the hardware counting is in units of 4 ps. These numbers
correlate to some degree with the Allan Deviation of the instrument for
shorter taus, but as taus is allowed to increase various limits kicks in.
It's been *years* since I ran one, I could be off on the 100 seconds ....
Most of the ones you see for sale have at at least one input channel blown out.. They are easy to fry and the front end chips aren't anything you can get off the shelf.
It's a nice bench-counter thought and is fairly flexible.
The HP5334A is the economy version of the HP5335A but has an additional
feature which is usefull for time-nuts... the binary output dumps the
unprocessed MRC values and can do that in a steady stream, allowing for
time-stamp records to be recorded. Together with picket fence it allows
a higher rate recording than the HP5335A.
Hmm, I have a HP5335A to repair. Probably the PSU.
Cheers,
Magnus
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