8.33 kHz channel spacing triples the number of available channels in the VHF aeronautical band. It does this by dividing each 25 kHz channel into three narrower channels. This spacing is mandatory in most of European airspace, with a few exceptions for emergency, search and rescue and data channels. Unlike 25-kHz channels, an 8.33-kHz frequency doesn't represent the actual transmit frequency but acts more like a designator. It's derived by adding or subtracting a fixed offset from the center frequency. This keeps the number of digits manageable, while still letting pilots and controllers distinguish channel spacing at a glance.
R&S®CMA180 radio test set
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