# Waves Question

1. Feb 22, 2005

### lektor

Hi, first time posting, nice forums :)

Recently in my preparation for my scholarship exams later this year, i was approached by a question which has me rather confused.

Im not neccesarily asking for the final definate answer, but it would be nice for some help on how to approach the problem.

Radio waves of frequency 600kHz are recieved at a location 10Km from the transmitter. The radio reception temporarily fades due to the interference between the direct beam and that reflected without phase change from a horizontal layer of charged particles formed in the atmosphere by a passing plane. Calculate the minimum height of the plane

formulas suggested were λ = dx/L

and dsinθ = mλ

p.s how do you draw the symbols ?

Last edited: Feb 22, 2005
2. Feb 23, 2005

### einstone

Welcome to the forum, Lektor.
Since the beam reaches the the receiver after the reflection, the reflection must have occured somewhere above the spot halfway between the receiver & the transmitter (i.e., 5km away from either).(I reckon this is what you couldn't hit upon.)If the height of the plane is H, the distance travelled by the beam is ( because the reflection didn't change the phase) 2* sqrt( H^2 + 5^2). This distance must exceed 10km by an odd number of half wavelengths.
Regards,
Einstone.