1. Advanced Radio and Radar
Part 4
Receivers

2. Introduction Y Y We know a basic radio system consists of -
a Transmitter
The Tx converts information
(voice, pictures or digital code)
into em radiation,
which then radiates to the Rx,
where is converted back into information.
and a Reciever. Tx Y Rx Y
Information
Transmitter
Receiver

3. Introduction MODULATION We also know that ‘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

4. λ = Aerials V F The first element in the process of receiving
a radio message is the aerial.
We know that the length of the aerial
dictates the frequency
at which it will transmit and receive.
An aerial can vary from a length of wire
to a complex array
selecting only certain frequencies. V = λ F

5. Aerials but whatever its shape, its purpose is to
detect the electromagnetic waves (‘em’)
and convert them into tiny voltages.
An aerial can vary from a length of wire
to a complex array
selecting only certain frequencies.

6. Aerials If an aerial in the form of a length of wire
is placed into an electromagnetic field,
tiny voltages are induced in it.
These voltages alternate
with the frequency of the ‘em’ radiation,
and are passed to the receiver circuitry
for processing.

7. Aerials Tuned Circuits. The signal strength the aerial inputs
to the receiver is very tiny –
( volts).
So the receiver circuits have to be
extremely sensitive,
and they must also isolate the wanted signal
from all the unwanted ones being received.
This is achieved by using
Tuned Circuits.
which allows a single frequency to pass,
filtering out all the unwanted signals.
5 micro volts

8. Let’s examine a basic receiver
The Receiver
Basic Diagram
The Receiver - Receives the signal from
the aerial (Ae)
Demodulator - Extracts the signal from
radio frequency RF
to audio frequency AF.
Audio Amplifier - increases the signal strength
for output to the speaker.
Let’s examine a basic receiver
and what it consists of. Y Ae
Loud
Speaker
Receiver
Demodulator
Audio Amplifier

9. The Receiver Basic Diagram Y In early models there were problems of -
Poor/Limited Selection
(ability to remain on station)
Poor Amplification/Fidelity
(strength & sound quality)
and Noise
(too much interference)
Receiver
Demodulator
Audio Amplifier Y Ae
Loud
Speaker

10. The Receiver The superheterodyne principle offers a way to overcome
some of these problems.
This involves the effect that one ‘sine wave’ has
over another adjacent ‘sine wave’,
of a different frequency.
For example -
two waves in the sea meeting and interacting
or the interaction of two AC electrical signals
of different frequencies

11. The Receiver When two notes of near equal frequency
sound together - a periodic rise and fall
in intensity can be heard - a beat.
The same applies to radio waves,
where the beat becomes an added frequency,
known as an Intermediate Frequency (IF).
This beat can be catastrophic !
And has even resulted in old,
badly designed propeller airliners
shaking themselves into fatigue failure
and even destruction !

12. The Receiver f1 + f2 Sum Frequency Let’s take two frequency waves
& f2
The upper wave, f1 has a lower frequency than f2
A composite wave would be –
This resultant wave is the
Sum Frequency
f1 + f2

13. The Receiver f2 - f1 Difference Frequency
Let’s take two frequency waves f1
& f2
If we join up the peaks and troughs
The resultant wave is the
Difference Frequency
f2 - f1

14. The Receiver f2 - f1 Difference Frequency
Let’s take two frequency waves f1
& f2
If we join up the peaks and troughs
If f1 = 248 kHz
and f2 = 252 kHz
The resultant wave is the
Difference Frequency
f2 - f1
then this new wave gives a beat of 4 kHz

15. The Receiver To overcome the receiver problems
(poor/limited selection,
poor amplification/fidelity,
excess noise and beating)
the Super-Heterodyne (superhet)
receiver was developed,
making use of these ‘beats’
by receiving lower frequency than Tuned Circuits.
This lower frequency can be processed
more effectively
than the higher radio frequencies.

16. The Superhet Receiver Basic Diagram Y Ae
output 1 2 4 5 6 3
1 RF Amplifier Amplifies and stabilises the signal.
2 Mixer Changes frequency. With the Local Oscillator (LO)
it combines to give Intermediate Frequency (IF).
3 LO With the Mixer it produces a constant frequency.
4 IF Amplifier Usually 2 or more stages. Amplifies the mixer output
(gives most of gain).
5 Demodulator Extracts the intelligence from RF to AF signal.
6 AF Amplifier Increases signal to required levels of output.

17. FM Receivers Reception on the AM bands is limited
in both quality of reproduction
and bandwidth availability.
FM systems are less likely
to be affected by "noise"
and give increased signal performance.

18. FM Receivers Y Y Remember the AM receiver
The FM circuitry is similar to the AM system
but uses a discriminator
(also called a ratio detector)
in place of a demodulator.
Receiver Y Ae
Audio Amplifier
Loud
Speaker
Demodulator
Carrier
Input Y Ae
Reference Source
Discriminator
Ratio Detector

19. FM Receivers Y The discriminator circuit has been designed
to detect small differences in frequencies.
These differences are converted to a voltage output
that represents the AF component input.
The FM circuitry is similar to the AM system
but uses a discriminator
(also called a ratio detector)
in place of a demodulator.
Carrier
Input Y Ae
Reference Source
Discriminator
Ratio Detector
Recovered
Signal
Loud
Speaker
Amplifier for Output

20. FM Receivers Y Y AM Receiver FM Receiver Ae Recovered Carrier Signal
Demodulator
Audio Amplifier Y
Loud
Speaker
AM Receiver
Carrier
Input
Recovered
Signal
FM Receiver
Amplifier for Output
Loud
Speaker
Recovered
Signal
Reference Source
Discriminator
Ratio Detector
Carrier
Input Y Ae

21. Check of Understanding
A tuned circuit is used to . . .
Filter out all unwanted signals.
Amplify all unwanted signals.
Select only unwanted signals.
Attenuate all unwanted signals.

22. Check of Understanding
What do FM receivers use
to demodulate signals?
Modulator
Discriminator
Amplifier
Mixer

23. Check of Understanding
What is the purpose of an aerial on a receiver?
To convert the electromagnetic waves (em)
into constant voltages.
To convert the electromagnetic waves (em)
into tiny voltages.
To convert the electromagnetic waves (em)
into large voltages.
To convert the electromagnetic waves (em)
into amplified voltages.

24. Check of Understanding
The superheterodyme receiver is used . . .
To operate a lounspeaker without
audio frequency amplification
For the reception of lower frequency signals than is possible with the tuned circuit receiver
When intermediate frequency amplification
is not require
For improved sensitivity and selectivity

25. Check of Understanding
In a radio receiver,
what is the process of converting
the radio signal frequency into audio frequency
known as?
Superhetrodyning
Re-amplification
Local Oscillation
Demodulation

26. Check of Understanding
This diagram shows a discriminator
(ratio detector)
what does the item ‘P’ represent?
Carrier Input
Reference Source
Recovered Signal
Output Amplifier

27. Check of Understanding
This diagram shows a discriminator system,
what does the item ‘W’ represent?
Receiver
Ratio Detector
Output Amplifier
Carrier Input

28. Check of Understanding
This diagram shows a discriminator
(ratio detector)
what does the item ‘X’ represent?
Carrier Input
Reference Source
Recovered Signal
Output Amplifier

29. Check of Understanding
This diagram shows a discriminator system,
what does the item ‘Y’ represent?
Receiver
Ratio Detector
Output Amplifier
Carrier Input

30. Check of Understanding
This diagram shows a discriminator system,
what does the item ‘Z’ represent?
Receiver
Ratio Detector
Output Amplifier
Carrier Input

31. Check of Understanding
In a receiver,
what is the purpose of
a radio frequency amplifier?
Amplify the signal after demodulation
Convert the signal to a lower frequency
Amplify and stabilise the signal
Demodulate the signal

32. Check of Understanding
In this diagram,
what does the block marked ‘R’ represent?
AF Amplifier
IF Amplifier
RF Amplifier
Carrier Input

33. Check of Understanding
In this diagram,
what does the block marked ‘S’ represent?
Amplifier
Mixer
Local Oscillator
Demodulator

34. Check of Understanding
In this diagram,
what does the block marked ‘T’ represent?
Demodulator
RF Amplifier
Mixer
IF Amplifier

35. Check of Understanding
In this diagram,
what does the block marked ‘U’ represent?
Local Oscillator
Mixer
IF Amplifier
Demodulator

36. Check of Understanding
In this diagram,
what does the block marked ‘V’ represent?
RF Amplifier
Local Oscillator
Demodulator
Amplifier

37. Check of Understanding
In this diagram,
what does the block marked ‘W’ represent?
Oscillator
RF Amplifier
IF Amplifier
AF Amplifier

38. Check of Understanding
What type of circuit is used in a receiver
to recover FM signals?
Discriminator
Modulator
Demodulator
Local Oscillator

39. Advanced Radio and Radar
End of Presentation