A high efficiency simple 2-transistor VHF amplifier electronic circuit project can be designed using this electronic circuit diagram . This VHF amplifier electronic circuit has a very high efficiency of about 16dB gain, and requires no tuning or alignment procedures. Wideband techniques have been used in the design and the circuit is equipped with a "lowpass" filter to ensure good output spectral purity. This VHF power amplifier circuit is specifically designed to amplify the output of 7mW to 10mW WBFM transmitters to a final level of 250mW to 300mW, after the filter.
The output of this stage is around 70mW of RF power.
The transistor is biased by means of R5, R6 and L6, and the residual DC current is set by R4. The input signal is coupled by C9 to the Base of the transistor.
The input signal from Q1 is coupled to the Base of Q2 via C7.The 78L08 voltage regulator is used to regulate the supply voltage to Q1 and the bias votages to both Q1 and Q2 so that the output RF power is relatively constant, even with large variations of supply voltage.
The output of the amplifier is filtered with a low-pass filter to reduce the output spurious and harmonic content.
The output filter consists of C3, C4, L1 and L2.
This RF power amplifier must be powered from a simple 12 volts DC power supply circuit.