# Homework Help: Fresnel zone question

1. Sep 6, 2010

### bos1234

1. The problem statement, all variables and given/known data
I've solved this question but I don't understand the conclusion the book says.

2 towers(transmitter and receiver), both of equal height(10m) and separated by a distance of 500m. f=800Mhz. Calculate first fresnel zone

First Fresnel zone has a radius of 6.84m at the midway point.

Then it further says that,
at a distance of 100m from either the transmitter or receiver, the first fresnel zone has a radius of 5.48m
. Consequently,all objects between the txer and rxer must be shorter than 3-4m in order to have the approximate equivalent free-space propagaion over the 500m path at 800MHz.

Firstly, when they say that "at a distance of 100m from either the transmitter or receiver" does that mean the dist. between reciever and txer is 100m? If so im getting 3.06 instead of 5.48m

Secondly, whats the point of finding this when the 2 towers are located 500m from each other>

relevant formula:
http://en.wikipedia.org/wiki/Fresnel_zone
F_n=....