Keysight Technologies N9340B, User Manual

Page: 77 / 172

Making Measurements
Demodulating an FM Signal
71
Demodulating an FM Signal
This section demonstrates how to demodulate and listen
to an FM signal using the built-in FM demodulator.
Using the built in FM demodulator you can tune to an
FM signal and view the results of the detector output as
displayed in the time-domain. Alternatively, the
demodulated signal is also available as an audio output
(to the speaker or headphone jack).
1 Perform a factory preset:
Press [Preset] (Factory Preset, if present).
2 Use a signal source or an antenna for an FM signal to
analyze. In this example the signal source is used
transmitting at 300 MHz with FM deviation of 10 kHz
and FM rate of 1 kHz.
3 Set the center frequency to the center of the FM
signal (in this case 300 MHz):
Press [FREQ] > 300 > {MHz}.
4 Set the analyzer to zero span for time-domain
analysis:
Press [SPAN] > {Zero Span}.
Press [BW/SWP] > {Sweep Time} > 4 > {ms}.
5 Turn off the input attenuation and turn on the optional
pre-amplifier:
Press [AMPTD] > {Attenuation} > 0 > {dB}.

Press {Preamp On}
6 Set the resolution bandwidth to capture the full
bandwidth of the FM signal. To calculate the required
bandwidth use
NOTE
If you are using a broadcast FM signal in the United States, for
example, the FM channels are broadcasting between 87.7 MHz
to 107.7 MHz. The optional preamplifier is essential for the
broadcast FM signal demodulation.