Chapter 2 81
Making Measurements
Example 6: AM and FM Demodulation
Example 6: AM and FM Demodulation
What is AM and FM Demodulation?
Amplitude modulation (AM) and frequency modulation (FM) are
common modulation techniques used to broadcast information. In the
United States and Canada, the AM broadcast band is 535 kHz to 1605
kHz, while the FM broadcast band covers 88 MHz to 108 MHz.
Demodulation of AM and FM signals can be done with any spectrum
analyzer with zero span capability and with a wide enough bandwidth
to fully encompass the modulated signal. An easier method of
examining a demodulated signal is to use the built-in AM and FM
demodulator and speaker in the 8560 E-Series and EC-Series spectrum
analyzers.
For simplicity, in our example we will demodulate only an FM signal. To
demodulate and listen to an AM signal, repeat the same steps, but
activate
AM DEMOD ON OFF instead of FM DEMOD ON OFF.
Spectrum Analyzer Functions Used
The following procedure illustrates the use of the built-in AM and FM
demodulator and speaker. The example includes tuning the spectrum
analyzer to a band of interest, activating and moving a marker to the
signal that is to be demodulated, and demodulating and listening to the
signal with the built-in demodulator and speaker.
Stepping through the Measurement
Set up the test
1. Provide a signal to the spectrum analyzer by connecting an antenna
to the input port of the spectrum analyzer.
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