Which type of modulation is commonly used for VHF and UHF voice repeaters?

The modulation most commonly used for VHF and UHF voice repeaters is Frequency Modulation (FM), which can also include Phase Modulation (PM) since they are closely related. FM is particularly advantageous in these frequency ranges because it provides greater noise immunity and improved sound quality over amplitude modulation methods, especially in mobile communications where signals may be more susceptible to interference.

VHF (Very High Frequency) and UHF (Ultra High Frequency) bands are used extensively for voice communications, such as those conducted by ham radio operators. Using FM allows for clearer transmission of voice signals and better performance in varied conditions, such as when the transmitter and receiver are in motion (as would be the case in mobile setups) or when there are obstacles that could distort or absorb signals.

Other modulation techniques like AM (Amplitude Modulation) and SSB (Single Sideband) are less common for these applications mainly due to their susceptibility to noise and interference. PSK (Phase Shift Keying), while efficient for digital data, is not suited for analog voice communications in this context. Therefore, FM or PM stands out as the best choice for voice repeaters in these frequency bands.