Specifications

98 Chapter 11
Demodulating AM and FM Signals
Demodulating an FM Signal Using the ESA-E Series (Requires Option BAA)
Demodulating AM and FM Signals
Demodulating an FM Signal Using the ESA-E
Series (Requires Option BAA)
This section demonstrates how to demodulate and listen to an FM
signal using the ESA built-in FM demodulator with option BAA.
Using the ESA’s 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) and as video output (on
the rear panel of the ESA).
NOTE FM demodulation is not available on the PSA Series spectrum
analyzers.
Step 1. Perform a factory preset:
Press
Preset, Factory Preset (if present).
Step 2. Use an ESG RF source or an antenna for an FM signal to analyze. In
this example an ESG is used transmitting at 300 MHz with FM
deviation of 10 kHz and FM rate of 1 kHz.
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.
Step 3. Before continuing with the demodulation of the FM signal, calibrate the
demodulator:
Press
System, Alignments, Align Now, FM demod.
Step 4. Set the center frequency to the center of the FM signal (in this case
300 MHz):
Press
FREQUENCY Channel, Center Freq, 300, MHz.
Step 5. Set the analyzer to zero span for time-domain analysis:
Press
SPAN X Scale, Zero Span.
Press
Sweep, Sweep Time, 4, ms.
Step 6. Set the resolution bandwidth to capture the full bandwidth of the FM
signal. To calculate the required bandwidth use
In our case the RBW should be: (2 x 10 kHz) + (2 x 1 kHz) = 22 kHz
With ESA’s 1-3-10 sequence RBW selections, choose the next highest
RBW of 30 kHz:
RBW 2 x Frequency Deviation()2 x Modulation Rate()+()=