1 (a) i) Describe how radiation from resonant LC circuit is increased by opening out the plates of the capacitor.

Answer: LC forms a turned circuit and opening the plats increases considerably the radiation of electromagnetic waves by the capacitor. A high frequency, the rate of formation and collapsing of the magnetic and electric fields will be so high that electromagnetic wave propagates as the fields will not reach the other plate.

ii) Calculate the dimension of straight wire half wave (λ/2) dipole antenna for use at 16MHz.

Anwer:

we know that C= f.λ

where: C is known as the speed of light which is a constant known 3x108m/s

f is the frequency in Hz and

λ is the wavelength in m

Data Formula Solution

C=3x108 c=fxλ λ=3x108/16x106

F=16GHz=16x106 λ=c/f λ=3x108x10-6/16

λ=? λ=3x108+(-6)/16

λ=3x108-6/16

λ=3x102/16

λ=300/16

λ/2=18.75m/2

λ/2=9.375m

b) The effective length of a vertical antenna may be increased by either using a loading coil or an inverted L configuration. Draw diagram to show these configurations and compare them in terms of efficiency of radiation.

Answer:

The effective length of a vertical antenna may be increased by inserting a loading coil in between the line and the antenna terminal so that it cancels out the capacitive reactance which is included in the feed point.

Inverted L on the is used in other to increase the resistance, for that end a horizontal portion is putted at the top of the antenna and it has the effect of increasing the current at the base of the antenna and makes the current distribution more uniform.

2 A vertical wire antenna is connected to a transmitter operating at frequency of 438kHz.

a) i) State the polarization of the radiation field.Answer: The polarization of radiation field in this case is said to be vertical.

ii) Calculate the wavelength of the signal.Answer:Data Formula Solution C=3x108 c=fxλ λ=3x108/438x103

f=430kHz=438x103Hz λ=c/f λ=3x108x10-3/438λ=? λ=3x108+(-3)/438 λ=3x108-3/438 λ=3x105/438 λ=300000/438 λ=684.93m

iii) Explain why a unipole antenna is used.Answer: An unipole antenna is used because it helps to reduce the length of the necessary dipole by a factor of two and and this results in a larger

directivity. For instance an AM signal is to be broadcasted at a frequency of 1605kHz, the height of the antenna would be 46.7 meters, unlike 93.45 meter that would be required if a half wave antenna was used.

b) Describe with the aid of diagrams the effect of on the radiation pattern of adding director and a reflector to a λ/2 dipole.

Answer:

Side view Top view

3 a) A vertical antenna is said to have a figure of eight polar diagram.

i) Sketch the polar diagram.Answer:

ii) Describe how it occurs by referring to the field components of an incident wave.Answer: A vertical antenna, the electric field is in the verticalplane and the magnetic field is in the horizontal plane so it is vertically polarized and an e.m.f of any incident wave vertically polarized will be induced into it.

c) Describe one use of this antenna.

Answer: It can be used as HF transmitting antenna since at this frequency range waves travel by means of multiple reflector and may reach thousand of km.

iii)

Level 5 Diploma in Telecommunications Engineering

Radio System ii

Assignment 1

Student details:

Name: Pedro Antonio da Conceicao Sanga

Number: 201305343

BIBLIOGRAPHY

*INTERNET

*BOOKLETS OF SOME TOPICS ABOVE GIVEN

*MY NOTES BOOK