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4.11 AM Measurement of AM Modulation
Signal
AM modulation signal can be demodulated from carrier
signal by spectrum analyzer's demodulation function and
displayed on the screen. In the following example, an AM
modulation signal input by signal generator (Agilent
E4421B) is as signal to be measured: carrier wave is
100MHz, -10dBm continuous-wave, modulation frequency:
1kHz, modulation depth:100%.
Operation steps:
1. Connect equipment
Connect signal output of signal generator with RF input on
the front panel of spectrum analyzer.
2. Use zero span to measure AM signal
1) Reset instrument
- Press PRESET key.
2) Set parameters
- Press FREQ key;
- Press[Center frequency] key,and input100MHz;
- Press SPAN key;
- Press [Zero span] key, set spectrum analyzer's span
as 0Hz;
- Press BW/SWP key;
74
- Press [Sweep time Auto Manual] key, set sweep time
in manual mode, and input 10ms;
- Press [Next page];
- Press [Signal sweep];
- Press AMP key;
- Press [Scale type Linear Logarithmic], set scale type
as linear.
3) Use marker to measure frequency of AM modulation
signal.
- Press
PEAK
key;
- Press
MARKER
key;
- Press [Difference] key;
- Press
PEAK
key;
- Press [Next peak] key; or press [Right peak] key or [
Left peak] key under PEAK key, search peak on the
right or on the left; read marker's frequency, i.e. frequency
of modulation signal.
3. Read measurement result
Measured cycle of modulation signal is 1.233ms, as shown
in Figure 4-15:
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