4-18 AM/FM/SSB Demodulation Chapter 4 — Spectrum Analyzer
4-18 MS20xxA VNA Master UG 10580-00166 Rev. C
4-18 AM/FM/SSB Demodulation
The VNA Master built-in demodulator for AM, narrowband FM, wideband FM and single
sideband (selectable USB and LSB) allows a technician to hear an interfering signal to ease
identification. The demodulated signal can be heard using either the built-in speaker, or
through a monaural headset connected to the 2.5-mm jack on the test panel.
Demodulation Procedure
1. Press the Shift key followed by the Measure (4) key and the AM/FM Demod soft key.
2. Press the
Demod Type soft key and select FM Wide Band, FM Narrow Band, AM, USB, or LSB to
match the modulation format of the signal.
3. Press the
Back soft key.
4. Press the
Demod Freq soft key and use the keypad or rotary knob to enter the center
frequency of the signal to be demodulated. For USB and LSB signals, fine tune the
signal by adjusting the
Beat Freq Osc. By default the BFO frequency is set to zero,
meaning that the re-injected carrier is exactly at the demodulation frequency. The
Beat
Freq Osc
soft key allows adjustment of the beat frequency oscillator to fine tune the
signal through a span of ±10,000 Hz.
5. Press the
On/Off soft key to enable the measurement.
6. Press the
Volume soft key and use the Up/Down arrow keys or rotary knob to change the
audio volume from 0% to 100%. For most headsets a volume of 40% is adequate.
7. The
Demod Time soft key sets the time the VNA Master will demodulate the signal. Enter
a value from 100 ms to 500 seconds.
10580-00166C.book Page 18 Thursday, February 21, 2008 12:52 PM
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