Dipole antenna is the antenna that a new ham or an experimenter erect first.This is becausethe dipole is cheap and easy to put up.It works well with a little effort.Here we will discusshow to calculate and costruct a dipole.
Calculation: The name 'dipole' implies that it has two poles.This antenna is generally calculated for half wavelength.The feed point impedence is normally 73 ohm above a certain height but it varies from 0 to 120 ohm at other heights.We will,however,use 72 ohm as it is used normally.75 ohm co-axial cable is used as the feed line.One can use a 1:1 balun between the antenna and feed line.The 'BALUN' will be discussed someday.Anyway,the length of a dipoleis given below.
Total length: L= 143/F
Where,
L is the total length of the dipole in meters
F is the frequency of operation (e.g F of transmitter or receiver) in MHz
Length of each part: = 71.5/F
Total Length in feet: L(ft)= 468/F(MHz)
You might have to adjust the length a bit for rosonance.
(To be continued..)
NB:For free ebooks on antenna just mail me at galib.ehobby@gmail.com
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