[time-nuts] Measurement of Rubidiums

Bill Hawkins bill at iaxs.net
Mon Jun 9 21:14:34 EDT 2008

I live in a depression pretty much surrounded by old oaks. I have
set to ignore anything below 30 degrees. Receivers are HP Z3801A's
with HP antennas 4 feet apart on one mast that takes them to the roof
line. Both see the same sat's but with different levels in the hundreds.
Lowest number is two, highest six.

I have two Racal 1992's operating. I use them in Phase A-B mode, with
one receiver to A and the other to B. The drift rate is slow, but they
do drift. I don't remember if there's a net drift, because I used them
against cesium and rubidium standards where there was a net drift, a few
years ago.

I suspect that your problem has to do with the way you are driving the
external standard input on the 1992. Try eliminating that problem by
using the internal standard and setting the function to Phase A-B.
You should see a number between 0 and 359 that has maybe 5 counts of
noise, but changes over hours, on the average.

Tell us what you see when you compare two receivers and pairs of
and standard. Be sure that the 50 ohm terminator light is lit on the
for inputs A and B.

If the numbers are unreasonable, tell us about the settings of your 1992
input options.

Bill Hawkins

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Jim Robbins
Sent: Monday, June 09, 2008 6:30 PM
To: time-nuts at febo.com
Subject: Re: [time-nuts] Measurement of Rubidiums

Hi all,

    Well, I have good news and bad news.
    The good news is that I believe I now know why I was getting the
strange readings on my Racal 1992 with the Thunderbolt GPS and/or the
Starloc II and my Rubidiums.  Neither GPS receiver was able to lock onto
enough satellites (if any).  The bad news is that that the failure to
lock is due to the location of my home/antenna out in the woods with the
HP GPS antenna up about 10 feet above the roof (i.e. 32 feet above
ground).  I am surrounded by trees in a sort of "race track" shaped
clearing, with the short axis closest woods being about 57 feet from the
antenna (both East and West sides) and having a height above the antenna
height of 38 to 48 feet.  The long axis woods is some 75 to 108 feet
from the antenna and having a height above the antenna height of between
18 feet (South) and 48 feet (North)!  The long and the short of it is
that the angle of view of the satellites is seriously blocked and varies
from 35 degrees to about 7 degrees in the South!

    Sorry that my contribution to the group is to reveal that you
probably can't use GPS if you live in a hole in the woods!  I've played
with the geometry and I'd need a very tall tower to get the angles all
down to 7 degrees or less.  I am discourged, to say the least.  Anyone
got any other ideas besides going back to Loran?

Jim Robbins

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