[time-nuts] OT - GPS and North

[Eric Garner]

alternately you could use a short-haul modem. I've used the ones from
Telebyte running over with good success. you can get up to 115.2 kbps
on ~1km of cable on some of them.

http://www.telebyteusa.com/shorthaulmodem.htm

-eric

On Mon, Nov 23, 2009 at 7:37 AM, Justin Pinnix <justin at fuzzythinking.com> wrote:
> 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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-- 
--Eric
_________________________________________
Eric Garner