Radio communication uses radio links to transmit information between a transmitter and receiver via air as the communication medium. It involves modulating a carrier signal at the transmitter and demodulating the signal at the receiver. The basic components of radio transmitters and receivers include antennas, oscillators, mixers, amplifiers, and modulators/demodulators. Key radio communication parameters that determine performance include sensitivity, signal-to-noise ratio, selectivity, transmit power, operating frequency, and modulation type.

1. RADIO COMMUNICATIONS
Dr. P Malindi
Walter Sisulu University

2. Contents
• What is radio communication?
• The functional block diagram of
radio/wireless communication system
• Basic radio communication parameters

3. What is radio communication?
• Communication that uses radio links to relay the information from
transmitter to the receiver & is used in radio, TV, cell phones, satellite,etc.
• It consists of a radio transmitter & a radio receiver that are linked by air as
the communication medium or channel
• The transmitter (Tx) prepares the information to be transmitted using
modulation (& sometimes also encoding)
• Receiver (Rx) recovers & reconstruct the transmitted signal using
demodulation (& decoding if signal was encoded at the Tx)
• Antenna acts as an interface between radio system & channel to convert
– modulated electrical signals into radio waves during transmission &
– from radio waves into electrical signals during reception
Transmitter Receiver
Communication
Channel
Antenna Antenna
Radio waves
Figure 1

4. Functional Block Diagram
• Figure 1 depicts radio communication in general; however,
the exact radio transmitters & receivers are as follows:
AF P/P Audio Amp Mod Amp
RF osc Buffer
Power
Amp
Mic
AF P/P
Reactance
Mod
Mic
LC
Osc
XN
Power
Amp
RF Amp Mixer
Local Osc
IF Stage Detector
Audio
Amp
RF Amp Mixer
Local Osc
IF Stage Detector
Audio
Amp
limiter
AM Transmitter
FM Transmitter
FM Receiver
AM Receiver

5. Functional block diagram: AM
Transmitter
• Mic – The microphone converts sound into electrical
signals.
• AF P/P- pre-amplifiers & band-limits the output of the mic
• Audio Amp - amplifies the incoming audio signal to a desired
undistorted level of amplitude.
• Mod Amp - amplifies the audio signal to a power level
suitable for modulating the carrier in the final power
amplifier
• RF Oscillator - generates a stable RF signal that is used as
the carrier frequency of the system
• Buffer - performs 3 functions: isolation, amplification &
frequency multiplication.
• Power Amplifier – modulates the carrier and amplifies the
modulated signal.
• Antenna – converts the modulated signals into radio waves

6. Functional block diagram: FM
Transmitter
• Mic – The microphone converts sound into electrical
signals.
• AF P/P- pre-amplifiers & band-limits the output of the mic
• Reactance Mod - converts the varying incoming audio signal
into a varying reactance
• LC Oscillator - generates an FM signal using its tuned circuit
together with varying reactance from the Reactance Mod &
in the absence of varying input, the oscillator will generate a
constant frequency signal without any frequency deviations
• Frequency Multiplier – performs frequency multiplication to
convert the generated narrow-band FM into wide-band FM.
• Power Amplifier –amplifies the modulated signal.
• Antenna – converts the modulated signals into radio waves

7. Functional block diagram: AM
Receiver
• Antenna – The antenna intercepts the radio waves & converts them to electrical
signals.
• RF STAGE – Selects & amplifies the incoming RF signal before feeding it to the
mixer.
• LOCAL OSC – generates a sinusoidal signal of constant amplitude with a
frequency that is IF above the selected, which is also applied to the mixer.
• MIXER – Accepts RF signal from RF stage & a sine wave from the local
oscillator, mixes them to produce a new set of frequencies, which includes the
sum and difference of the two frequencies
– The output of the mixer stage is coupled to the IF stage by a tuned circuit that has a band pass
filter response to pass only the difference of the two frequencies
– This difference is called the intermediate frequency, IF, for AM it is 455 kHz, for FM it
is 10.7 MHz and for analogue microwave, the IF is 70 MHz.
• IF Stage - provides bulk of radio-frequency signal amplification around IF
• Detector – demodulates the down-converted RF signal (i.e. extract the audio
frequencies from the RF signal)
• Audio Amp – amplifies demodulated signal to drive the loudspeaker.
• LOUDSPEAKER – the loudspeaker converts the amplified audio signals into
sound

8. Functional block diagram: FM
Receiver
• Antenna – The antenna intercepts the radio waves & converts them to electrical
signals.
• RF STAGE – Selects & amplifies the incoming RF signal before feeding it to the
mixer.
• LOCAL OSC – generates a sinusoidal signal of constant amplitude with a
frequency that is IF above the selected, which is also applied to the mixer.
• MIXER – Accepts RF signal from RF stage & a sine wave from the local
oscillator, mixes them to produce a new set of frequencies, which includes the
sum and difference of the two frequencies
– The output of the mixer stage is coupled to the IF stage by a tuned circuit that has a band pass
filter response to pass only the difference of the two frequencies
– This difference is called the intermediate frequency, IF, for FM it is 10.7 MHz
• IF Stage - provides bulk of radio-frequency signal amplification around IF
• Limiter - makes sure that the amplitude of the FM signal fed into the FM detector
has constant amplitude.
• Detector – demodulates the down-converted RF signal (i.e. extract the audio
frequencies from the RF signal)
• Audio Amp – amplifies demodulated signal to drive the loudspeaker.
• LOUDSPEAKER – the loudspeaker converts the amplified audio signals into
sound

9. Basic Radio Communication
Parameters
• Sensitivity – ability of the receiver to amplify weak signal
• Receiver sensitivity limit (RSL) – weakest signal level that can be
successfully received by the receiver
• Signal-to-noise and distortion (SINAD) – is a measure of the
degradation of the required signal by unwanted signals & is
expressed as a ratio
• Selectivity – ability of the receiver to select the required signal
(station or channel) while rejecting all the others
• Transmit (or output) power – power that is produced by the
power amplifier stage of the radio transmitter
• Operating frequency – unmodulated carrier frequency of the
radio system
• Modulation – this is the type of modulation that is used to
superimpose the information into the carrier signal