James Lux wrote:

Hi James,

that's easy for you at Nasa! You have rotary antennas, good receivers and so on...
I thought to GPS sats because there are cheap receivers all around, and hoped
the 1 PPS would tell something, so freeing me from considering doppler, relativity etc.

Anyway, please let me know if you find any easily detectable signals that doesn't
require a tracking antenna.

Bye,
Antonio I8IOV

iovane@inwind.it wrote:

GPS will not help you at the PPS level, but you can avoid the tracking
antenna anyway. The doppler-stuff and alot of other things is very well
described. It is not hopeless, but not a very easy feather out of the
hat thing.

Cheers,
Magnus

On 6/28/09 3:23 PM, "iovane@inwind.it" iovane@inwind.it wrote:

There are lots of LEO satellites with signals detectable by an omni antenna.
All you need is a downconverter to something easily digitizable (e.g. That
you can feed into a sound card) and your trusty GPSDO to generate another
signal that you digitize at the same time.

As for (cheap) downconverters... That's a bit trickier. Maybe an eval board
from NatSemi or Maxim

Find one of those databases of LEO satellites and their frequencies, then
look for a convenient band.

On 6/28/09 4:35 PM, "Magnus Danielson" magnus@rubidium.dyndns.org wrote:

Basically, it's a sort of tedious whittling away.  Once you have the basic
capture receiver working, it's just modeling stuff and writing countless
Matlab to remove this, that, and the other thing.  Check out the paper by
Peter Yoho for the analysis.  My paper (with Jon Adams) describes the
hardware.

Isn¹t Inmarsat in a Clarke Orbit?  If the propagation path for the solar
eclipse shadow experiment runs through the eclipse with the path from Clarke
orbit to you, then there's tons of signals available to look at.

On 6/28/09 10:48 PM, "Lester Veenstra" m0ycm@veenstras.com wrote:

I think the idea was to look for jumps in a crystal oscillator when it goes through the shadow of a total eclipse. My original suggestion was to look for LEO satellites which had conveniently monitorable oscillator frequencies. Someone else suggested using Inmarsat (because they have a L-band pilot tone), but I think the Inmarsat birds are in Clarke orbit, so you'd have to pick your ground station location (essentially in line with the sun and the bird) to do the test.

Now this begins to make some sense;

Of course the geosync satellites do go into eclipse season trice a year,
during which each day the satellite is passing through the Earth's shadow
for a variable period.

To pass though the shadow of a solar lunar eclipse, the eclipse would have
to be visible on the ground at satellite sub-satellite point ( nominal, the
equator). For the Inmarsat's this would be at:

24.8 E
25.1 E
64.5 E
109.0 E
143.5 E
178.1 E
218.0 $
261.9 E
262.4 E
306.0 E
344.5 E

But, since there are satellites virtually anywhere along the arc, there is
no reason to restrict observations to INMARSAT. But INMARSATs do provide a
easy target  for an observer with simple L-Band equipment.

Of course I would expect to see a shift in an onboard crystal frequency (but
not a "jump") simply from the thermal changes.

Lester B Veenstra  MØYCM K1YCM
lester@veenstras.com
m0ycm@veenstras.com
k1ycm@veenstras.com
-----Original Message-----
From: Lux, James P [mailto:james.p.lux@jpl.nasa.gov]
Sent: Monday, June 29, 2009 7:36 PM
To: lester@veenstras.com; 'Discussion of precisetimeand frequency
measurement'
Subject: RE: [time-nuts] Orbiting crystals

.................
I think the idea was to look for jumps in a crystal oscillator when it goes
through the shadow of a total eclipse. My original suggestion was to look
for LEO satellites which had conveniently monitorable oscillator
frequencies. Someone else suggested using Inmarsat (because they have a
L-band pilot tone), but I think the Inmarsat birds are in Clarke orbit, so
you'd have to pick your ground station location (essentially in line with
the sun and the bird) to do the test.

Lester Veenstra wrote:

It was assumed that the crystals was locked to Cesium or Rubidium, and
hence it would chase up the error.

Cheers,
Magnus