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

Brooke Clarke brooke95482 at att.net
Thu Aug 26 15:17:23 UTC 2010

Hi Mike:

Trimble made a number of orientation GPS systems that used multiple 

The problem with a mag compass is that the Earth's mag field is stronger 
in the up/down direction (in N. America) than it is horizontally.  So 
either the compass needs a bubble level or a 3-axis accelerometer and 
correction firmware.  Also they don't work well near ferrous metal.

PS the Polaris Guide has a built-in mag compass with digital readout to 
1 degree.
I find that it needs to be calibrated every time I want to use it.  This 
requires holding it level and turning in a circle.

A practical solution may be to get a used transit, like the Leitz 115A.  
It's made of brass (as are all the transits I know of) and has a nice 
mag compass.  It also has an adjustable offset feature so that the 
compass will read true bearings.
It could be setup on the ground at a distance from the tower about equal 
to the tower height.  It also should be possible, by moving the transit, 
to get the transit on the bearing line between the tower and the 
target.  This has the advantage that the person operating the transit 
can also help align the antenna.

Have Fun,

Brooke Clarke

Mike Feher wrote:
> 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
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

Have Fun,

Brooke Clarke

More information about the time-nuts mailing list