Robotron Pty Ltd WRG3P Manuel D’Utilisation

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To select the modulation mode, click on the appropriate Mode button in the
Demodulator panel:

The real-time spectrum display shows the output of the receiver (i.e. the
intermediate frequency signal) as it is applied to the PC sound card. When
you press the mode buttons, you will note that the central highlighted region
of the spectrum changes its width. This corresponds to the IF (intermediate
frequency) filter bandwidth associated with the different modulation modes.
For example, standard AM mode has 6 kHz bandwidth, while narrow AM
(AMN) uses 4 kHz bandwidth. The CW mode uses a narrow bandwidth of
500 Hz. You will see the trace color change from white to yellow where the
spectrum falls within the filter bandwidth. This indicates that you are only
receiving the yellow part of the displayed spectrum and the surrounding
frequencies are rejected.

If you mistune the receiver somewhat, you will see the spectrum shifting.
This assists you to tune the receiver right to the center of the transmitter
frequency, and to select the correct AM mode to avoid interference from
adjacent signals.