Frequency Modulation Flashcards
What is frequency modulation?
Frequency modulation is where the frequency of the modulated wave is determined by the amplitude of the modulating frequency when superimposed onto the carrier frequency
If the amplitude of the modulating wave increases, the frequency of the carrier wave will also increase
How is a FM signal easily identified on the kit?
It’s not!! We do not use this kit to identify FM
signals
In what bands are you most likely to find frequency modulated signals?
VHF and UHF
How is the modulation index (MI) worked out?
MI = fd / fm
Modulation index = frequency deviation / frequency modulation
What is frequency deviation?
It is how far the carrier frequency deviates from the Centre Frequency (the frequency occupied by the carrier in an unmodulated state)
What is the centre frequency?
The frequency occupied by the carrier when in an unmodulated state
How does the amplitude and frequency of the modulating frequency effect the deviation of the carrier?
The greater or higher the amplitude of the modulated wave, the greater the deviation of the carrier
The rate at which the carrier deviates is dependant upon the frequency of the modulating wave
How is bandwidth for FM signals worked out? What is the formula?
FM bandwidth = 2(fd + fm) Hz
2 x (frequency deviation + frequency modulation) Hertz
What is carrier swing?
It is the difference between the highest and lowest frequencies the modulated wave can attain.
The swing is twice the frequency deviation
What is meant by deviation ratio?
It is the ratio of the minimum frequency deviation and the highest permissible modulating frequency
What is meant by modulation index?
Modulation index is a decimal number representing he ratio of the frequency deviation and the highest frequency of the modulating wave
