[time-nuts] HP Z3801A, GPS vs UTC?

J. L. Trantham jltran at att.net
Sat Jun 11 20:16:24 UTC 2011

I have been wondering about this.

Since leap seconds accumulate from time to time, there must be a
'difference' between GPS and UTC.  Is the difference related to the rotation
of the earth around it's axis and around the sun and thus the need to add a
second or so from time to time as we do with leap year or is there a
difference in the reference oscillator frequency between the two that allows
a 'drift' of a second or so from time to time?  I suspect the former.


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Magnus Danielson
Sent: Saturday, June 11, 2011 8:47 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] HP Z3801A, GPS vs UTC?

On 06/11/2011 02:11 PM, Ron Hahn (EI2JP) wrote:
> On 6/7/2011 10:40 PM, cook michael wrote:
>> Le 07/06/2011 21:15, rtm at lcs.mit.edu a écrit :
>>> I have an HP 58503A. It has an "Option H14,H19" sticker on the back. 
>>> The circuit board has "58503-60001 Rev C" stamped on it. It has been 
>>> running continuously and locked to GPS for a few days, and it knows 
>>> the correct number of seconds between GPS and UTC.
>>> The unit displays GPS time, without the leap seconds correction. The 
>>> front-panel display says "GPS xx:yy:zz", and ":system:status?" says 
>>> "GPS 1PPS Synchronized to GPS Time", not "to UTC" as the manual 
>>> shows.
>>> I'd be much obliged if anyone could tell me how to get the unit to 
>>> display UTC instead of GPS time.
>> I think these use a similar command set to the Z3801A
>> try
>> :diag:gps:utc?                    should show 0 if the unit is in GPS,
>> 1 if UTC
>> if that gives coherent results, try
>> :diag:gps:utc 1
>> to force the mode
> Colleagues,
> For someone who is not understanding these modes, can you explain what 
> is this difference between UTC and GPS time?  I have a HP Z3801A which 
> I have been using for some years.  Do I need to change this to UTC 
> time?

If you only wish a 10 MHz and PPS, no. GPS time will do just as well. If you
also want UTC time for NTP server for instance, then you do want 
either to use the UTC mode or let the server know it runs on GPS time 
and compensate itself.


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