Content-Transfer-Encoding: 8bit
Message-ID: <5.1.0.14.0.20020101114249.01df2650@pop.tiscalinet.it>
Date: Tue, 01 Jan 2002 11:47:45 +0100
To: rsgb_lf_group@blacksheep.org
From: "Marco Bruno IK1ODO" <spin.elec@tiscalinet.it>
Subject: LF: GPS-based Frequency Standard
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>


Hi all,
Dexter W4DEX asked about frequency standards on the LOWFER
reflector. I presume that the subject may be of interest also there
in times of very narrow band communications.

The question was:
 >Is there anyone on this list who is familiar with Brooks Shera's
 >GPS-based Frequency Standard project which was published in QST, July
 >98?  Info can also be found at:
 >
 >http://www.rt66.com/~shera/

The Brooks Shera's project is very good, but not inexpensive.
For best results you need a Motorola UT+ GPS receiver. I bought it
new three years ago for about $200 including the antenna.
The PCB and components cost about $100, then you need a
stable OCXO. I use a surplus unit by Oscilloquartz, coming from
an Omega receiver. The best choice for cost vs. quality is an HP
10811A, contained in many instruments, of wich the more common
is the 5328A-H99 universal counter, available probably around $150.
Sometimes it contains the 10544A oscillator; if possible look for the
10811A, it has better stability, less noise and less power drain.

If you have to buy all the parts you spend about $450. The project is
not very complex, but you have to understand operation and tweek
with time constants and receiver settings, then monitor it for some
week to verify performance. From the point of view of a standard
frequency aficionado (as I am...) it is VERY interesting. For general
purpose use it is quite complex to manage; but when it works you
forget it.

Other possibilities are:
1) the HP 10811A alone. An excellent oscillator, and you may expect
some parts in 10^-8 per year from a good unit operated continuously.
But keep a spare unit... I've seen some of them "die" of quartz
inactivity. And you must have access to a primary standard for
tuning and checking it.
2) a Rubidium standard. A cheap one is worth $200-250 (check Ebay).
You get probably some parts in 10^10/year from an Efratom M100,
but again you need a way of checking it (need a Cesium!)
3) a Cesium standard. Now, it's a primary one!. Absolutely not
suggested to the average amateur, since the initial cost may be low
(some $2000 or $3000), but the tube has short life and it is VEEERY
expensive.
4) an HP Z3801A. An embedded GPS standard frequency receiver like
the Brooks Shera project, but simpler to use and already boxed!
You add power, a PC and a GPS antenna, and get 10 MHz.
Performance very close to the Brooks Shera project, cost about $450
on Ebay, varying availability.  I have one working at the QRL, and I am
happy about it. I use it to check the long term stability of our Cs and Rb,
and it is a good performer.

If you need more info, let me know.

73 ES HNY - Marco IK1ODO