Spectrum Analyzer Measurement Guide : Spectrum Analyzer : AM/FM/SSB Demodulation
 
AM/FM/SSB Demodulation
The built‑in demodulator for AM, narrowband FM, wideband FM, and single sideband (selectable upper sideband (USB) and lower sideband (LSB) signals) allows a technician to hear an interfering signal. The demodulated signal can be heard using either the built‑in speaker or a monaural headset connected to the 2.5 mm jack on the connector panel.
Procedure
1. Press the Shift key followed by the Measure (4) key. Then press the AM/FM Demod submenu key.
2. Press the Demod Type submenu key and press FM Wide Band, FM Narrow Band, AM, USB, or LSB to match the modulation format of the signal.
3. Press the Back submenu key.
4. Press the Demod Freq submenu 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 submenu key allows adjustment of the beat frequency oscillator to fine tune the signal through a span of ± 10000 Hz.
5. Press the On/Off submenu key to enable the demodulation.
6. Press the Volume submenu key and use the up or down arrow keys or the rotary knob to change the audio volume from 0% to 100%. For most headsets, a volume of 40% is adequate.
7. The Demod Time submenu key sets the time that the instrument will demodulate the signal. Enter a value from 100 ms to 500 seconds.