AMATEUR RADIO TRAINING Transmitters & Receivers Release: v1.21 hamtrain.co.uk

TRANSMITTERS & RECEIVERS Block Diagrams Modulation Types Station Setup

Transmitter Basics A radio transmitter has four basic stages: 1. Audio Stage Gets and amplifies weak signals from the microphone 2. Frequency Generator Creates the radio signal on the right frequency 3. Modulator Mixes the radio and audio signals together 4. 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

Receiver Basics A radio receiver has three basic stages: 1. Tuning / RF Amplifier Tunes into the required frequency Amplifies the weak signal so that it can be used 2. Detector Extracts the audio from the radio signal. Often called “demodulation” There are different types of detector for each modulation type 3. Audio Amplifier Amplifies the audio and feeds it to a loudspeaker or headphones

Receiver Block Diagram 1: Tuning and RF Amplifier 2: Detector (also referred to as a “De-modulator”) 3: Audio Amplifier 1 2 3

Modulation AM FM

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

Morse & Data CW Audio CW Signal CW: Tones generated using a Morse key Data: Audio tones generated via a computer soundcard or a TNC (Terminal Node Controller)

Transmitting At Foundation, you can only use commercially-purchased transmitters (no construction) You must only transmit on allocated frequencies and must not exceed permitted power levels ‘Over-modulating’ or ‘Over-deviating’ may result in interference to to adjacent frequencies as well as poor audio quality. Take care with audio levels (microphone gain, shouting, data signals from a computer) You must stay in-band, not cause interference, and test your 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 Don’t just learn the numbers – learn the meanings Modulation Types Amplitude Modulation Frequency Modulation Transmitter usage Take care with audio levels, so you don’t over-modulate or over-deviate Test equipment to ensure it stays in-band

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