[Fwd: [TowerTalk] GPS receivers]

[Jim Brown]

On Sat, 18 Sep 2004 15:48:39 -0400, Steve wrote:

>Having a GPS 
>receiver in my pocket to capture the lat/long of the potential tower 
>site would be quite helpful as well as eliminate a potential source of 
>error that could be introduced in finding the site on a map. 

My friends who claim to be educated in matters of GPS say that 
because of the manner in which the system is modulated for security 
reasons, consumer units are limited to accuracy on the order of several 
meters in plan and tens of meters of elevation. A search on google for 
GPS accuracy a year or so ago appeared to confirm that my friends 
were correct.  

It is, of course, possible that this has changed, but it is consistent with 
my own results using the GPS plug-in to my Handspring. Like you, I find 
the GPS quite handy in figuring out where I am and at what elevation. 
When I am moving fast enough that successive readings are at widely 
separated points (in a car or aircraft), it gives very usable information on 
direction of travel. But if I try to determine the direction of north or the 
azimuth of a street by briskly walking a straight line, the results are far 
less consistent.  

I would guess that even mine, which is three years old and discontinued 
(but still works great), would be more than sufficient for placing your 
location on a topo map. But I would suspect that even the best non-
security blocked GPS would be insufficient for more critical work like 
surveying. 

BTW, my plug-in is a Magellan, and it works well on the dash of a car 
unless it is badly shadowed by surrounding objects.


Jim Brown  K9YC