[DSP-10] GPS Standard : HPZ3801A or Shera project ?

Tue, 7 May 2002 09:22:42 -0500

Two of us locally bought HP Z3801As 6 weeks or so ago.  Took a little
fiddleing around to figure a couple of things out.  K8CU's web page is
INVALUABLE in getting these up and running.  (Note: if your computer will
accept 0 and +5 for RS232, you don't need the RS422 interface.  But not all
computers will work with those voltage levels)

Bob (the other ham) has been running LORAN and WWVB comparisons for years
(he consults professionally) and has been tracking the 10 MHz output from
the Z3801A.  Bob's several days of strip chart comarison show well less than
200 ns maximum deviation between the GPS and either LORAN or WWVB.  Most of
the deviations occur at sunrise/sunset, when both WWVB and LORAN have
"problems" with skywave/groundwave transitions.  

Bottom line: if the green "GPS LOCK" LED is ON, then the 10 MHz output IS 10
MHz within 2 or 3 parts in 10E-11.  The local XTAL oscillator takes some
time (a couple of days) to stabilize, but it will come to nearly the same.
(At least mine has;  I happened to check it this morning and it was 2.5
usec/24 hours.  This is slightly better than 3x10E-11.)

MY OPINION: the Z3801A is the best deal around if you need (want) accuracy.
Unpack it, connect the antenna, connect power, and it works.  (Power may be
a problem.  You'll most likely need a -48 volt power supply.  These units
are coming out of cell phone sites.)

Both Bob and I got ours from "next2nucomputers" out of Knoxville, TN.  They
currently have some on e-bay for $299 (Price is coming down -- we paid $350
of ours.) Shipping included.  You will also need a good outdoor GPS antenna
and good feedline.  We found the better the antenna, the faster the lock,
and better the accuracy (what a surprise!).

The Z3801A has only one connector for 10MHz output (BNC).  You'll need to
make up some sort of buffer amplifier/distribution if you will be using the
signal in several places.  Check W7CQ's web pages for a 10MHz buffer/amp.

73 Donn
WA2VOI/0

-----Original Message-----
From: Rocco Tanucci [mailto:[email protected]]
Sent: Tuesday, May 07, 2002 4:09 AM
To: [email protected]
Subject: [DSP-10] GPS Standard : HPZ3801A or Shera project ?

Dear All,
I would like to have a GPS frequency standard but I'm
not sure on
Brooks Shera project or  the Hewlett Packard Z3801A.

The price for Z3801A is 399$ (in the surplus market),
the price for 
Shera project is almost the same ( GPS receiver 150$,
HP oscillator, 150$, etc.)

Any suggestion ?

Regards.
Rocco

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