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

• A. Amplitude modulation
• B. Single sideband
• C. Frequency modulation or Phase modulation
• D. Quadrature amplitude modulation

Answer: (C)

VHF packet radio transmission primarily utilizes Frequency Modulation (FM) or Phase Modulation (PM) due to several technical advantages these methods offer.

Frequency Modulation is particularly well-suited for VHF transmissions because it is more resistant to noise compared to Amplitude Modulation. This is essential in maintaining a clear signal over the often variable conditions of VHF bands, which can be susceptible to interference and fading. Similarly, Phase Modulation, while technically distinct from FM, offers comparable benefits in terms of spectral efficiency and resilience to interference.

Packet radio communication requires reliable and error-free data transmission. The FM and PM methods help achieve this by allowing receivers to accurately demodulate signals despite the potential for background noise, ensuring that data remains intact during transmission.

While other modulation types have specific applications in amateur radio and can carry voice or other forms of communication, they do not provide the same level of noise immunity and effectiveness for data transmissions in the VHF range as FM and PM do. Thus, these modulation techniques are the standard choice for VHF packet radio communication.