1. Advanced Radio and Radar
Part 2
Wavelength, Frequency and Modulation

2. Introduction Using ‘em’ energy has many advantages
compared with sound energy:
Speed of travel is extremely fast,
The speed of light - 3 x 108 m/s, (ms-1)
300,000,000 meters/s
or 186,000 miles/second.
b. ‘Em’ waves travel through a vacuum
so can be used for communication in space.
‘Em’ waves travel a long way for any given
power rating.

3. Introduction ‘Em’ waves travel a long way for any given power rating.
Pioneer 10 was launched in 1972.
Originally giving 140 Watts of power,
when it sped past Saturn the radio power
had decayed to 100W.
The radio was turned off by NASA in 2003
when Pioneer was 8 billion miles away !!
and taking 12 hours for the radio signal
to reach Earth.
At that time it it was transmitting a mere 40W
at a frequency of 2 GHz,
barely enough for a domestic light bulb.
(a microwave blasts out 800w)
For Example –

4. Wavelength & Frequency
The wavelength , is calculated by dividing
the velocity of the wave V, by its frequency F.
Remember
Velocity = Frequency x Wavelength
Velocity V is the speed of light - 3 x 108 m/s,
300,000,000 m/s
Frequency F is the number cycles per second,
KHz, MHz etc.
1 KHz = 1,000 cycles
Therefore a frequency of 1KHz
gives a wavelength of 300km
300,000,000 λ V F =
1,000

5. Wavelength & Frequency
The length of the aerial dictates the frequency
at which it will transmit and receive.
Remember that
Velocity = Frequency x Wavelength
The most useful form of this expression
is to calculate wavelength  for aerial selection.
λ/2 for horizontal polarisation, and λ/4 for vertical
are particularly efficient aerial lengths.
Knowing the wave velocity and frequency,
we can calculate the wavelength
and the best aerial lengths for that frequency. = λ V F

6. Wavelength & Frequency
We know wavelength , is calculated
by dividing velocity V, by frequency F.
Remember that
Velocity = Frequency x Wavelength
So what aerial length
would suit a frequency of 200 KHz?
λ = 1500 metres
Therefore an aerial length of
750 or 375 metres would give the best results.
(λ/2 for horizontal, λ/4 for vertical polarisation) = λ V F
3 x 108
(= 3 x 100,000,000 = )
300,000,000
λ =
200 x 103
(= 200 x 1,000 = )
200,000
(= 1500 / 2 = 750)
(= 1500 / 4 = 375)

7. Wavelength & Frequency
Remember –
The shorter the length an aerial becomes,
The higher the optimum frequency
it will transmit and receive.
The longer the length an aerial becomes,
The lower the optimum frequency

8. Advanced Radio and Radar
Modulation

9. Introduction In 1901 Marconi was the first man
to transmit and receive transatlantic radio signals.
The radio waves were sent
by switching the transmitter “OFF” and “ON” –
Morse Code.
Although effective, this system depended on
the operators learning Morse Code.

10. Introduction MODULATION For a system that everyone could use,
some way of making the radio waves
carry more information had to be found.
‘Em’ energy can be made to carry speech
if low-frequency currents produced by speaking
are combined with the high-frequency currents
that produce radio waves.
This combination process is called
MODULATION

11. Modulation For the transmission of speech and music,
the sound waves are converted by microphone
into an oscillating electric current
which varies at the same frequency
as the sound wave.
This is called an "audio-frequency" current.
An electronic circuit called an oscillator
then produces an ‘em’ “carrier wave”.
(by converting energy
into a periodically varying electric output)

12. Modulation MODULATED This carrier wave is a continuous
high radio-frequency (RF) current,
having a fixed frequency from the range
100 KHz to 1 GHz.
The audio-frequency (AF) current,
and the radio-frequency (RF) current,
are mixed in the transmitter
so that the carrier wave is
MODULATED
so as to duplicate the sound waves
fed into the microphone.

13. Modulation Amplitude Modulation (AM), Frequency Modulation (FM).
A carrier wave
can be modulated in two ways,
either by
Amplitude Modulation (AM),
or by
Frequency Modulation (FM).
The simplest form of
Amplitude Modulation (AM)
is switching the transmitter "ON" and "OFF"
to interrupt the carrier wave.

14. Modulation This modulates the amplitude from max to zero,
and then back to maximum,
producing pulses of Morse Code
(dots and dashes)
The simplest form of
Amplitude Modulation (AM)
is switching the transmitter "ON" and "OFF"
to interrupt the carrier wave.
ON OFF ON OFF ON OFF
D A S H D O T D A S H

15. + = Modulation Whist this system is ideal for Morse,
it is not good enough for speech or music,
because sound requires more variations
to achieve an accurate reproduction.
An improvement is to alter the amplitude of the
high frequency tone (the carrier wave)
in step with the lower frequency audio tone. + =
Carrier Wave
Audio Tone
Modulated Wave

16. Check of Understanding
One advantage of ‘em’ waves
is that they travel -
A long way for a given power
A short way for a given power
Forever for a given power
A long way for no power

17. Check of Understanding
What is the optimum length
for a half-wave aerial that requires
to transmit and receive 1 MHz signals?
600 metres
300 metres
150 metres
3 x 108
(= 3 x 100,000,000 = )
300,000,000
λ =
1 x 106
(= 1 x 1,000,000 = )
1,000,000
15 metres

18. Check of Understanding
The shorter the length of an aerial becomes:
The lower the optimum frequency that it will transmit and receive.
The more efficient it is.
The higher the optimum frequency
that it will transmit and receive.
The less efficient it is.

19. Check of Understanding
What is the wavelength of
a wave of frequency 1 KHz
given the speed of light is 300,000,000 m/s?
30 m
30 km
300 m
300 km

20. Check of Understanding
If the velocity of a radio wave is
300,000,000 m per sec,
and the wave frequency is 10 KHz,
what would be the wavelength?
30,000 metres
3,000 metres
300 metres
3 x 108
(= 3 x 100,000,000 = )
300,000,000
λ =
10 x 103
(= 10 x 1,000 = )
10,000
30 metres

21. Check of Understanding
If a wavelength is 40 metres,
what would the best aerial length be?
1 or 4 metres
5 or 10 metres
10 or 20 metres
20 or 40 metres

22. Check of Understanding
What type of modulation
does Morse Code use?
Wavelength Modulation
Frequency Modulation
Carrier Shift Modulation
Amplitude Modulation

23. Check of Understanding
A few more questions.
What is meant by the term Modulation?
What do the initials AF and RF stand for?
True or False ? FM is a higher frequency than AM.
What is the great drawback with the AM system?
True or False ? AM is more prone to atmospheric and
manmade noise?
ANSWERS
The combination of low and high-frequency currents into radio waves
Audio Frequency and Radio Frequency
True
The need for such a large bandwidth in a limited frequency spread

24. Advanced Radio and Radar
End of Presentation