[time-nuts] Slightly OT - GPS-Based Accurate Direction Finding

[Mike Feher]

Back in the very late 80's we at Magnavox did propose a system, for the
military, utilizing 4 GPS antennas to give us azimuth, roll, and, pitch.
This other information at the time seemed important in case a soldier would
jump up or down from the HMMWV possibly loosing the satellite after initial
acquisition. Of course, stabilizer legs on the vehicle were a simpler
solution. This was to point a 45 GHz satellite antenna. The GPS antennas
were separated about 1 meter apart in more or less a square configuration. I
believe even 3 would have worked. The concept and theory looked real good on
paper, however, it was unfortunately never built due to lack of funding. I
do not recall if it was ever proprietary or otherwise, as the concept at the
time seemed fairly obvious to us. As pointed out, later solutions were
simply a flux gate compass and adequate tracking/pointing algorithms.
Magnavox had many years of experience with the flux gate compass technology
considering the millions of sonobouys that were built. Just an FYI - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ 07731
732-886-5960 



  

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of David Smith
Sent: Thursday, August 26, 2010 10:10 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] Slightly OT - GPS-Based Accurate Direction Finding

Thanks for all the interesting responses.

Some background - I'm needing an accuracy of 1 degree or better.  The 
experiments are using digital communication modes and sometimes aircraft 
scatter so signals are regularly inaudible and often non-existent, so 
peaking "by ear" is not usually an option.

I've paced out direction using a handheld GPS (GPSMap 60CSX) and this 
gives reasonable results if there's a reasonable baseline.  It's a bit 
impractical when operating from a firetower though!

Using Sun/Moon/Stars is difficult when there's cloud. We've tried using 
Sun RF Noise, but accuracy declines significantly when the sun is high 
in the sky.

VOR is an interesting suggestion, but a very sharp (and large) antenna 
would be needed and multi-pathing may cause problems.

So, my interest turns back to a GPS-based solution and the military 
units suggested by Brooke look perfect ... except that they are most 
likely a restricted export and unavailable to us Down Under.

Other links on Brooke's site have lead me to many papers researching 
GPS-based attitude systems.  I note that the Uni of Calgary have 
developed a package called HEADRT+ that can take raw measurements from 
several GPS mounted on a small baseline and produce attitude 
information.  This is the sort of thing I'm after, but I get the 
impression that licensing costs are high.

As Atilla says, the software is probably not that fundamentally 
complicated.  However, the devil is possibly in the detail of aligning 
sample timing, positioning ...

Any other suggestions?

Regards,
Dave

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