VHF Preamplifier for FM Broadcasting 88MHz-108MHz (Band II)

Above schematic diagram is the circuit of VHF pre-amplifier for FM broadcasting (frequency 88MHz-108MHz, band II)

The circuit is working with two 2N3819 FET's in cascode configuration. The lower FET works in common source mode, while the upper FET, works in common gate, realising full high frequency gain. The bottom FET is adjustable allowing a peak for a particular station.


The FET 2N3819 is designed for RF amplifier and mixer applications operating up to 450MHz, and for analog switching requiring low capacitance.

Coils Specification:

1. L1 4 turns of 18swg air spaced with a 1 cm diameter, the tap is one turn up from earth end...
2. L2 4 turns of 18swg air spaced with 1 cm diameter. The coupling coil is 1 turn interwound from the supply end. Enamel coated wire must be used.

VHF Preamplifier for FM Broadcasting, circuit source: zen22142.zen.co.uk

About RF Amplifier
An RF power amplifier is a type of electronic amplifier which is utilised to convert a low-power radio-frequency signal into a larger signal of significant power, usually for driving the antenna of a transmitter. It is usually optimized to have high efficiency, high output Power (P1dB) compression, good gain, good return loss on the input and output, and optimum heat dissipation.

The basic applications of the RF power amplifier include driving to another high power source, driving a transmitting antenna, microwave heating, and exciting resonant cavity structures. Among these applications, driving transmitter antennas is most well known.
More explanation about power audio amplifier can be found at wikipedia.org

This is a demonstration about 01A RF Amplifier which is build used old tube component to amplify the signal.

Watch the video: