[time-nuts] Cesium C Field Set?

John Ackermann N8UR jra at febo.com
Fri Feb 11 09:00:22 EST 2005

Brooke Clarke wrote:
> Hi:
> Here's a plot of the time interval between a zero crossing of the 1 MHz 
> cesium output vs. an average of 1,000 GPS 1 PPS.  It's been going for 
> over 10 days and I think the wanderings are due to using different 
> satellites in the GPS constellation.  Has anyone else plotted GPS vs. 
> Cesium, i.e. are these results reasonable?
> http://www.pacificsites.com/~brooke/pdf/sn1227_CF544.pdf
> I have the ionospheric correction turned off on the GPS receiver, should 
> it be on?

Hi Brooke --

You seem to have quite a bit more noise on your plot than I am getting 
with mine, though my current run isn't as long as yours (and I'm 
obviously still trimming the C field).

My current run versus GPS is at 
http://www.febo.com/time-freq/plots/hp5061a.html and versus LORAN-C is 
at http://www.febo.com/time-freq/plots/hp5061a-loran.html.  The script 
updates the plots every 15 minutes.

My GPS measurement setup is a Motorola UT+ receiver mounted on a TAC-2 
board driving the stop input of a 5370B counter, with the 1pps from the 
5061A driving the start input.  The reference for the counter is my 
5065A Rb.

The LORAN measurement setup reads an Austron 2100F chart output in 1us 
FS mode.  I'm tracking 8970M from Dana, Indiana, which is something like 
150 miles from my location.  An HP 3421A data acquisition box 
(essentially, a multiplexer coupled to a 5 1/2 digit DMM and GPIB 
interface) reads the chart output.  I use minimum GRI averaging in the 
receiver and take readings once per second, averaging for 100 seconds.
The absolute offset between the two pulses is about 1.5us; my plotting 
software normalizes from that.  I'm averaging for 600 seconds.


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