AMATEUR RADIO TRAINING

Transmitters & Receivers

v1.11 © essexham.co.uk

TRANSMITTERS & RECEIVERS

• Block Diagrams• Modulation Types• Station Setup

Transmitter BasicsA radio transmitter has four basic stages:

Audio Stage• Gets signals from the microphone

Frequency Generator• Creates the radio signal on the right frequency

Modulator• Mixes the radio and audio signals together

RF Power Amplifier • Increases the combined signal and feeds to the antenna

Transmitter Block Diagram

1: Audio Stage

2: Modulator (More on this shortly)

3: Frequency Generator (also referred to as an Oscillator)

4: RF Power Amplifier

3

1 2 4

Receiver BasicsA radio receiver has three basic stages:

Tuning / RF Amplifier

• Tunes into the required frequency

• Amplifies the weak signal so that it can be used

Detector

• Extracts the audio from the radio signal. Often called “demodulation”

• There are different types of detector for each modulation type

Audio Amplifier

• Amplifies the audio and feeds it to a loudspeaker

Receiver Block Diagram

1: Tuning and RF Amplifier

2: Detector (Also referred to as a “De-modulator”)

3: Audio Amplifier

1 2 3

Amplitude Modulation (AM)

Audio Signal

Carrier

Modulated signal

AM Transmitter Block Diagram

Audio Stage RF Power Amp

Frequency Generator

Modulator

Frequency Modulation (FM)

Audio Signal

Carrier

Modulated signal

FM Receiver Block Diagram

Tuning & RF amp Detector Audio Amplifier

AM vs FM

Audio Signal

AM Signal

FM Signal

TransmittingAt Foundation-level, only commercially-purchased transmitters can be used (no construction)

You must only transmit on allocated frequencies and at permitted power levels

‘Over-modulating’ or ‘Over-deviating’ may result in interference to other channels as well as poor audio quality. Take care with audio levels (microphone gain and shouting)

You must stay in-band, not cause interference, and test transmitters “from time to time”.

Station Setup• Microphone• Power Supply• Transceiver (transmitter & receiver)• SWR Meter• RF Filter• ATU• Antenna

Summary• Block Diagrams

• Remember the diagrams for transmitters and receivers

• Modulation Types

• Amplitude Modulation

• Frequency Modulation

• Station Setup

• Setting up a station correctly is one of the Foundation practicals

TRANSMITTERS & RECEIVERS

Any questions?

essexham.co.uk/train