[time-nuts] OT - GPS and North

[Rex Moncur]

Given that we cannot do it with one GPS in a fixed position I would like to
get people's ideas on whether there is a reasonable cost way (say less than
$2K) to do it with two GPSs to get within a say half a degree.


The application is to find azimuth headings for Amateur radio microwave or
lightwave experiments. One cannot normally do star shots due to either day
light or clouds.

Let us assume that you can run the two GPS's over a baseline of 100 meters.
At present I can get to within about plus/minus two degrees by walking an
inexpensive handheld GPS over a baseline of 100 meters but I want to do
better than that. For the hopefully more accurate measurement I would place
one GPS and antenna at the microwave dish or lightwave transmitter and the
other would be set up 100 meters away roughly in the direction one needed to
beam. When a bearing was found one could either readjust the position of the
remote GPS antenna to improve the accuracy or just allow for any error by
beaming by this amount to the GPS unit. 

Let us  assume that both GPS antennas are in a fixed location and the
results can be averaged over say 30 minutes to improve the accuracy.  I
assume also that many of the errors due to propagation would cancel over
such a short path.  The data from both GPSs would be fed to a laptop over
say RS232 line which I hope would work for 100 meters (perhaps 50 meters
each way if necessary).  The Laptop would have software to process that data
and provide a bearing between the two antennas. Can anyone comment on:

(a) the likely accuracy of such a system
(b) whether there is any software out there that can do this.
(c) the recommended GPS units for this application.
(d) whether there is something one could purchase as a complete package at a
reasonable cost (ie less than $2k)

73 Rex VK7MO





-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of iovane at inwind.it
Sent: Monday, 23 November 2009 8:08 AM
To: time-nuts
Subject: Re: [time-nuts] OT - GPS and North

Thanks all.

The conclusion seems to be that an ordinary and stationary GPS receiver with
a single 
omnidiretional antenna knows very well where satellites are relative to the
true North, 
and where the true North is relative to satellites, but doesn't know (more
precisely: 
can't indicate, as it lacks another reference) where satellites or the North
actually are. 
Eventually this appears quite obvious.

Antonio I8IOV


_______________________________________________
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.