What type of modulation is commonly used for VHF packet radio transmissions?

VHF packet radio transmissions predominantly utilize frequency modulation (FM). This method is well-suited for the conditions and requirements of VHF, offering good noise immunity and efficient use of bandwidth. FM allows for reliable signal transmission over varying distances and conditions, which is crucial for data communication in amateur radio applications.

Phase modulation (PM) is closely related to frequency modulation and is also used in some digital modes; however, FM is the primary choice for VHF packet radio due to its established protocols and widespread usage among amateur operators.

Other modulation types like single sideband (SSB), amplitude modulation (AM), and phase-shift keying (PSK), while relevant in various contexts, do not offer the same level of effectiveness for packet data operations in VHF bands. SSB is typically used for voice communications and is more bandwidth-efficient than AM, but it does not perform as well as FM for the kind of digital packet data transmissions commonly utilized by amateur radio operators. AM is less efficient in spectrum use and more prone to interference, which makes it unsuitable for packet data. PSK is generally used in specific digital modes, but it's less common for VHF packet radio transmissions, which primarily rely on the reliability and advantages of FM modulation.