[OZAPRS] Hang Glider APRS

[Carl Makin]

Hi Andrew,

On 19/04/2006, at 6:35 AM, Andrew Rich wrote:

> In contact with the local hang glider club. One guy is going to fly  
> 100 Km's
> cross country.
> I measured it with a comms test set - 168 mW.

Looking around the net I found;

http://www.auf.asn.au/comms/vhfradio.html

which said;

The rule-of-thumb: the maximum direct path distance (the distance to  
the horizon) between an aircraft and a ground station, in nautical  
miles, is equal to the square root of the aircraft height, in feet,  
above the underlying [flat] terrain. Actually it is 1.06 times the  
square root of the height but for our purposes that can be ignored.

Theoretical LOS distance to horizon
Aircraft height (feet) -	Maximum LOS distance (nm)
10 -	3.2
100 -	10
1000 -	32
5000 -	70
10000 -	100


-----------------------

According to figures plugged into this website;

http://www.isghq.com/calc/path_loss.php

100 miles at 0.17W with 0 dbi gain antennas at each end over a free  
space path have a received signal strength of around 2uV which should  
be audible making the curvature of the earth the limiting factor.

------------------------

So if the aircraft is at 1000 feet you should be able to hear it  
around 50Km away and it would need to be at around 5000 feet to be  
heard at 100Km.

Except of course if there are mountains, or other obstacles like 747s  
in the way.

This is of course all theory, your mileage may vary! <grin>


Carl.
(vk1kcm)

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