Radio Transmitter Amplification in the VHF Radio Spectrum

Initially it was vacuum tubes, particularly the tetrode and pentode tubes, commonly used for amplification. These vacuum tubes provided the necessary gain and power handling capabilities required for VHF radio transmission. However, vacuum tubes were bulky, required high operating voltages, and were less efficient compared to later semiconductor technologies like the [MOSFET]. Despite these drawbacks, vacuum tubes were extensively used in radio transmitters until the advent of solid-state technologies.

Bipolar junction transistors (BJTs) were commonly used for solid-state amplification in radio transmitters operating in the VHF (Very High Frequency) radio spectrum. BJTs were advantageous for VHF applications due to their high-frequency response, making them suitable for amplifying signals in this frequency range. Additionally, BJTs offered smaller size, lower power consumption, and greater reliability compared to vacuum tubes, making them a preferred choice for solid-state amplification in VHF radio transmitters before the widespread availability of MOSFET technology.

The MOSFET is currently the most common means for amplification in the VHF radio spectrum by operating in its enhancement mode. In this mode, the MOSFET is biased to allow current flow between its source and drain terminals when a sufficient voltage is applied to its gate terminal. By modulating the gate voltage, the MOSFET can amplify incoming radio frequency signals. MOSFETs offer several advantages for VHF amplification, including high gain, low noise, and good linearity. They can be integrated into small, lightweight packages, making them suitable for use in portable and mobile VHF radio equipment such as transceivers, broadcast transmitters, and radar systems. Additionally, advancements in MOSFET technology have led to improved efficiency and reliability, further enhancing their suitability for VHF amplification applications.