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Re: LF: GPS Signals Accurate Now!!!

To: [email protected]
Subject: Re: LF: GPS Signals Accurate Now!!!
From: "Andy Talbot" <[email protected]>
Date: Thu, 4 May 2000 21:24:12 +0100
Reply-to: [email protected]
Sender: <[email protected]>
Unfortunately Magellan appear to be the odd ones out on GPS receivers.  I
have a Magellan Trailblazer, circa 1993-4 which is almost certainly similar
to yours, and there is no trace of a 1 PPS signal inside the unit; I
searched very hard for it !   In the end I gave up and bought a Garmin GPS25
module from TAPR.  That turned out to be a good move as the device is very
very much better at locking up (1 minute fom cold instead of up to 20
minutes) with more info available in the NMEA sentences - and of course the
1 PPS.

Since SA was turned off, over the last two hours the mean position of my
house has drifted just 2 metres RMS with an absolute worst case shift of
3.6m.  I reckon that with a locking system like the Shera one and a good
stable ovened VCXO, a frequency standard to rival Rubidium and verging on
Caesium  accuracy may now be possible.    Getting a good enough VCXO will be
the difficult part.

Andy  G4JNT

-----Original Message-----
From: Alberto di Bene <[email protected]>
To: [email protected] <[email protected]>
Date: 04 May 2000 16:53
Subject: Re: LF: GPS Signals Accurate Now!!!


While we are discussing GPS, I have a question for all of you.
I bought a few months ago an OEM 5000  GPS board, made
circa 1993 by Magellan, because someone had told me that
on the interface there were available the 1 pps signal derived
from the received signals from the satellites, with the accuracy
and stability of their Cesium clocks, +/- the SA.

I was intending to homebrew something similar to the Shera
project appeared in a past issue of QST.

I have been unable to find that 1 pps signal, however. It just seems
not to be present on the interface. But there is a hope.
A few pins do not have signal on them, as seen on the 'scope,
but they have traces on the PCB leading somewhere. My last hope
is that the 1 pps signal must be enabled by some command to the
GPS unit.

Can anybody shed some light on this ? Anybody on this list that
has experience with the Magellan OM 5000 ? Thanks for any advice.

Alberto    I2PHD





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