eolas/zk/Radio_transmitters_and_receivers.md

tags
radio ham-study

Radio transmitters and receivers

Transmitters

Radio transmission comprises four stages:

1. Audio stage or "amplification"

• The weak signals from the microphone are amplified

2. Frequency generation via an oscillator

• The carrier wave is generated

3. Modulation

• The carrier wave and audio signal are combined

4. RF power amplification

• The combined signal is increased and fed through to the antenna

The following are important considerations:

Incorrect setting of the oscillator can result in operation outside of the amateur band and cause interference to other users

The microphone gain should not be set too loud as this will cause distortion. Furthermore, too loud a signal causes over-modulation on AM and over-deviation on FM which again could cause inteference.

The RF power amplifier must be connected to a correctly matched antenna to work properly. If not, damage can be caused to the transmitter.

Receivers

Radio reception comprises three stages:

1. Tuning/RF amplifier

• The receiver is tuned to the required frequency and the weak incoming signal is amplified so that it can be used

2. Demodulator

• Extracts the original audio signal from the modulated radio signal, separating the signal from the carrier.
• Each type of modulation type (FM, AM, SSB etc) has its own demodulator

3. Audio amplifier

• Amplifies the recovered signal and feeds it to a loudspeaker or headphones