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Re: [TowerTalk] GPS Receivers

To: towertalk@contesting.com
Subject: Re: [TowerTalk] GPS Receivers
From: N7KA@comcast.net
Date: Sat, 09 Apr 2005 14:51:57 +0000
List-post: <mailto:towertalk@contesting.com>
I think the question about the GPS receivers was to help set up a 5 GHz 
backbone.

Now the discussion has been the ability of a GPS receiver to assist in this 
effort.

I would think that depending on the distance between the 2 positions (antenna 
locations) that a few feet would NOT make any difference.

We just recently did a 10GHz shot over a 100 mile distance and the GPS helped 
to get "ball park" locations then the antennas on both ends were rotated for 
maximum signal strength.  Each end taking turn peaking the RX signal.  I would 
doubt that either antenna being proposed has a rotation indication that would 
be able to resolve a few feet of placement of antenna on the other end of the 
link. Besides do the antennas to be used have a very sharp narrow pattern? Our 
antennas were 2M in diameter BTW.

I use a GPS receiver when I am 4X4ing.  In most cases the ISGS Topo maps are 
fairly accurate when the GPS coordinate is over layed onto the map. (Digital 
mapping and track logs are great, BTW).  Just using Topo maps would allow 
placing both ends of a link with enough accuracy except for the VERY narrowest 
of beam patterns from the antenna.  I do agree with others that altitude on the 
"consumer" GPS receiver does leave a LOT to be desired.  I only use altitude as 
a "ROUGH" reference and not for any other navigation purposes. However I WILL 
depend on my GARMIN 2+ for location.  Have driven in on a trail then driven out 
the same or next day and GPS readings were the same. This is very evident when 
you make a track log going in then follow that route coming out.  BTW, did this 
in full darkness on one trip and I had 100% confidence in what the GPS was 
telling me.

One thing to be careful of is to make sure any map DATUM compares to the DATUM 
on the GPS.  Most folks use WGS84 on the GPS, whereas most topo maps have NAD27 
(or even earlier).  There will be some difference in location but its not much, 
under 100 meters in most cases.

This might be a case of ditch the technology and just go to work.

73 de Arne N7KA
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