Module 3 Flashcards
What is Modulation?
Transmitter creates RF carrier wave on required frequency
Mixies in the information to be transmitted
How does AM and FM work?
Amplitude modulation: changing amplitude of signal
Frequency modulation: changing frequency of signal
How do morse and data work
CW(carrier wave): tones switched on-and-off using a morse key
Data: audio tones generated via a computer
How do sidebands work
What are the pros of using them
What frequencies should you use each type
When modulating a carrier in AM, idential signals are created at lower and higher frequencies
Can get better results if all transmit power is used to transmit just one (LSB or USB)
LSB occurs under 10MHz
USB occurs above 10MHz
Four stages of a transmitter
Audio stage: gets and amplifies weak signals from microphone
Frequency generator: creates the carrier signal on the right frequency
Modulator: mixes radio and audio signals together
RF power amplifier: increases the combined signal and feeds to the antenna
Potential issues with transmitter operation
If oscillator isn’t set correctly, may transmit outside amateur band
RF power amp must be connected to a matched antenna or may damage transmitter
Potential issues with transmitter audio levels
Excessive amplitude modulation causes audio distortion and intererence with adjacent channels
Excessive frequency deviation causes interfence with adjacent channels
Set mic gain correctly
If using data, check audio levels from computer arn’t too loud
What can you only do at foundation
Only use commercially availiable transmitters and kits
Must only transmit on allocated frequencies and must not exceed permitted power levels
Stay in-band, don’t cause interference and test transmitter occasionally
Three stages of a receiver
Tuning/RF amplifier: tune into required frequency, amplifies the weak signal
Demodulator/detector: extracts the audio from the radio signal
Different types for each modulation type
Audio amplifier: amplifies the audio and feeds it to a speaker
What does SDR stand for
What do they do
Software Defined Radio
Receives radio signals from antenna and digitises the signals for processing software
Three stages of an SDR Receiver
Incoming signals converted using ADC
SDR seperates signal into seperate frequency components
Required signal selected using filter, demodulation carried out in software
DAC used to convert for speaker
Four stages of an SDR Transmitter
ADC converts speech from microphone
Modulated radio signals generated using software
DAC converts it back into signal
Power amplifier amplies signal
