VHF and HF Characteristics RNAV

VHFVHF —Very High Frequency comms are space waves, meaning they propagate in a straight line (and thus are line of sight), whereas HFHFHF —1) Radio Waves: High Frequency2) Human Performance: Human Factors —1) Radio Waves: High Frequency2) Human Performance: Human Factors comms are sky waves, meaning they propagate up to the ionosphere and back, and so can travel many hundreds of miles. This accounts for the difference in the way engineers transmit their sidebands.

With VHFVHF —Very High Frequency comms, because of the shorter range there is no need to minimise the sidebands in order to extend range, so there are two sidebands for VHFVHF —Very High Frequency comms, either side of the carrier frequency. However, for HFHF —1) Radio Waves: High Frequency2) Human Performance: Human Factors comms (and HFHFHF —1) Radio Waves: High Frequency2) Human Performance: Human Factors —1) Radio Waves: High Frequency2) Human Performance: Human Factors Volmet), because of the longer range only a single sideband is transmitted in order to maximise the power available to transmit the signals a long way. This does not matter as the sidebands are mirror images of each other, but does require specialist transmitting and receiving equipment.

Both types of comms use AMAM —Amplitude Modulated. The frequency ranges are 2-22MHz for HFHFHF —1) Radio Waves: High Frequency2) Human Performance: Human Factors —1) Radio Waves: High Frequency2) Human Performance: Human Factors and 118-137MHz for VHFVHF —Very High Frequency. Do not get the communications bands confused with the frequency bands.