Hi Hugh,
Enjoying your stories.
On 2019-01-21 01:57, Rice, Hugh (IPH Writing Systems) wrote:
Like all breakthrough measurements, the next 20+ years was spent refining the concept.
Better "front end" amplifiers, able to measure low amplitude signals. Faster
counters, that could capture higher frequency signals. Microwave front ends, to either
divide the signal by 8 or 16 or whatever before being counted, or using some other down
conversation technique. Somewhere in the early 1970's (guess), the reciprocal counter
was invented. Rather than open the gate for 1 second, use the input signal to open the
gate for one period, and count a very high frequency time base instead. It was much
faster, and for lower frequency signals, much much higher resolution. Now, if you had a
~1KHz unknown signal, rather than only getting 4 significant digits in a one second
measurement, if you counted a 100MHz time base for 1 millisecond, you would 5 digits of
resolution. Open the gate for a thousand cycles, and 8 digits of resolution were
available.
The HP5360A calculating counter was the first reciprocal counter that I
know of, released in 1970.
The reciprocal counter principle can be found described in HP AN200:
http://www.hpmemoryproject.org/an/pdf/an_200.pdf
The premium universal counter in the early 1980's was the 5370A/B. It's specialty was extremely
high precision time interval measurements, with resolutions down to 20 pico seconds. An idea
was made to extend the time interval measurement into continuous real time, and measure dynamic
time intervals, as a function of time. HP called this "Modulation Domain" analysis. I
think that David Chu, one of the senior scientists at SCD in the 1970s and 1980s was a key inventor
of this. The 5371A was the outcome of this work. It was followed by the 5372 and 5373.
There also was a lower cost version call the 53310 ("Stonehenge"?). The measurement
was novel and unique. You all know what oscilloscopes and spectrum analyzers do, but this was a
new spin: You could look at the phase of a signal as a function of time.
David Chu is a good name as one search for HP patents.
The really shining details about the 5371 series of products is that the
event rate can be up to 10 MHz or 13,3 MHz depending on mode. The
resolution is 200 ps. I think the main step with the 5372A was the
hardware histogram, that would accumulate histograms faster than the CPU
would. You would need to adhere to some limitations, but gets much
higher speeds and hence higher amount of counts in return. For the type
of applications it was intended, it was a huge step forward.
We still operate a 5372A in the lab.
Thanks again for a nice tale. I just wanted to add a few comments that
may be useful.
The HP Application Notes is always rewarding, just as the old HP Journal
numbers.
Cheers,
Magnus
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