HP 5345 Counter

© Brooke Clarke, N6GCE

HP 5345A Counter


HP 5345 Counter NSN 4931-01-039-4040

This  counter has a 12 digit 7-segment LED display and what's important for me has an HP-IB computer interface.  Measures up to 500 MHz without a plug-in. (Mine measures over 600 MHz at power levels as low as -21 dBm.)  It also accepts an external reference between 1 and 10 Mhz.  Has a noisy cooling fan and is a heavy 3 Unit high rack mount instrument.
Shortly after turn on the frequency of a 600.0 MHz input signal read high by about 3 Hz.  After a few hours of warm up time the frequency is reading low by 0.4 Hz. i.e. 6E-10 error, not bad.

Note that there is no need for adding a 5253A Plug in to the 5345 counter, it will count to over 500 MHz without any plug ins.

Note that the plug ins for the 5345 are larger than those for the 5245 so a 10590A Plug-in adapter is needed.


This counter has phenomenal resolution!  It turns out that internally there are two counters going all the time and the display is calculated by doing math on them.  When making a time interval measurement you would not think that the Gate Time control would not have any meaning, but that's not the case.  If  you are measuring a short time interval, say 1 micro second and set the gate time to 10 micro seconds then the counter will make repeated measurements until the accumulated gate time exceeds the selected gate time, effectively averaging readings and extending the resolution.  It's more awkward than a simple averaging type selection, but provides fantastic resolution.  You can see femto seconds this way.

I think the sequence for small engineering prefixes is:
<base unit> (E0), milli (E-3), micro (E-6), nano (E-9), pico (E-12), femto (E-15), atto (E-18).

HP Journal June 1974

There were a number of new concepts introduced in the HP 5345 and these are covered in the June 1974 issue of the HP Journal.

Counter Patents 

My web page started Dec 2006 relating to frequency or Time Interval patents.


TM 9-4931-509-34P
Mainframe counter, Hewlett-Packard Model 5345A (NSN 4931-01-039-4040);
Frequency Plug-In, Hewlett-Packard Model 5257A (4931-01-040-1492);
Video Plug-In, Hewlett-Packard Model 5261A (4931-01-040-1493);
Frequency Plug-In, Hewlett-Packard Model 10590A    (6625-00-544-3971),
Frequency Plug-In, Hewlett-Packard Model 5355A (6625-01-111-1074) AND
Video Amplifier Hewlett-Packard Model K87-59992A (6695-01-129-0246) 
11 March 1983, 72 pages

TB 9-6625-1996-35
Calibration Procedure for Frequency Counter, Hewlett-Packard Model 5345A AND 5345A/E28  



USM-207() NSN 6625-00-911-6368

These had Nixie tube displays and had a single plug in slot that would accept a number of accessories.  Measures up to 100 MHz without a plug-in.  This is different from the 5245 counter.
TM 11-6625-700-10  Operator's Manual Digital Readout Electronic Counter, 48 pgs, Oct. 1966 
TM 11-6625-700-14-1 Operator's, Direct Support, 494 pgs, Dec. 1973
TM 11-6625-700-24P  Parts & Tools USM-207 & USM-207A, 152 pgs, March 1979
TM 11-6625-700-25    Maintenance, 264 pgs, Oct 1966

Back to Brooke's Products for SaleTime & Frequency, Electronics, Home page

page created 19 April 2003