[time-nuts] OT - GPS and North

[Justin Pinnix]

Hi Rex,

Sounds like a neat application.  100 meters might be a bit long for RS-232.
I was taught that 50 feet is the limit for 9600bps.  You may need to use
RS-422 (balanced version of 232), low capacitance cable, or a lower baud
rate.  Since you're a ham, you could also do it wirelessly over UHF packet.
You might even be able to use existing APRS hardware, provided it leaves you
enough significant digits.

73 de AJ4MJ

On Sun, Nov 22, 2009 at 8:39 PM, Rex Moncur <rmoncur at bigpond.net.au> wrote:

> 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
>
>
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