[time-nuts] Which HP Frequency Counter?

[Angus]

A lot depends on the resolution you need and what all you want to use
it for, but it might also be worth looking at some recent Fluke
counters.

The PM6681 has a nominal rating of 300MHz on it's main input, although
it may read rather higher. It has 1M or 50R input res, and can
tolerate up to 12V rms. Also, its nominal time interval resolution of
50ps single shot and 1ps averaged can be quite useful.

The PM6680B is only rated at 225MHz, but it's cheaper, and sometimes
turns up with a high frequency channel at a reasonable price. GPIB was
an option with this one, so if you want that, you would have to check
that it's fitted.

It might also be worth checking if a separate prescaler would be ok
for your high frequency use, rather than having to find (and pay for)
a counter with a high freq input. 
An active probe could be used to reduce the loading, but they tend to
be expensive to buy.

Sometimes an HP53131A also turns up at a decent price, but probably
not with a high frequency channel. Input "damage level" is quoted at
5V rms for it. 
Personally, I really like the PM6681 since it's so capable, and I find
it much easier to use if the settings have to be adjusted much - but
the HP has an RS232 port which makes logging the data very simple on
any computer.

Angus.


On Sat, 08 Mar 2008 17:49:02 +0100, you wrote:

>Dear group,
>
>I consider buying a used lab frequency counter / timer --preferably 
>HP/Agilent-- covering from few mHz to perhaps 400 MHz.  I'm worried 
>that models handling high frequencies seem to be limited to under 100 
>mV input signal max. I don't want to destroy an input channel each 
>other day when calibrating/repairing some instrument.  Also are there 
>instruments with high impedance input? 50 Ohm is not quite right for 
>investigation in the guts of most designs.
>
>
>Is it possible to find a not-too-old model under $800?  I would like to 
>find something in France or UK or Europe, but it seems hopeless in this 
>budget.  I would favor a repairable model (with available service docs 
>& schematics).
>
>Your expert advises are more than welcome!