[time-nuts] Pulse width for start signal for HP5370

Tom Van Baak tvb at LeapSecond.com
Sun Sep 4 07:07:56 UTC 2011


Do you have an oscilloscope handy? When doing precision
time interval measurements it's useful to take a look at what
the counter inputs actually look like. Use a BNC tee and a 1M
scope probe (so as not to artificially load the counter input).

For pulse inputs it should help you set the DC trigger level
appropriately. I usually use 0.5 or 1 or 2.5 VDC. But seeing
the actual waveform helps me decide.

For CW inputs you will probably want to set the counter to
AC coupling and zero volt trigger.

Some counters give you a choice of 50R or 1M termination.
Be careful with that. In some cases the waveform is much
cleaner with 50R. In other cases 50R puts way too much
load on the source and you trigger level or risetime suffers.


> Following a suggestion given to me I am using   a 1PPS signal to "START" the
> HP5370.
> The "STOP"  is  the normal  the DUT 10 Mhz.
> The pulse comes from a Z3801 rear Db 25 connector.
> The counter seems to work ok with this except the level control does not
> have a lot of range.
> Too far CW and the level light stays on, to far CCW and the level light
> goes.
> There is some range but not a lot.
> Does seem normal to you folks?
> Paul A. Cianciolo
> http://www.rescueelectronics.com/
> "Time is relative"  Abert Einstien circa 1950
> "Relatives use up all my time"  Lisa Cianciolo circa 1983

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