The circuit design employs a VHF amplifier adjusted in such a way that it will operate in the frequency range of 88 to 108 MHz, as part of the Band 2 Radio Spectrum or the FM radio broadcasting range
The 2N3819 is an all purpose JFET which offers good performance at mid to high frequencies and a low cost type. It has low noise and leakage, very high system sensitivity, high speed switching capability, wideband high gain at 100 MHz, high low-level signal amplification and high quality of amplification. In this circuit, the two 2N3819 is configured in cascode to increase the current-source performance of the circuit by obtaining higher gain, higher output impedance, higher input-output isolation, higher input impedance, or higher bandwidth. Cascode is a two-stage amplifier that reduces the sensitivity of the circuit to the voltage supply fluctuations and extends the operating voltage beyond its recommended 5.5 V rating. The only disadvantage is that it requires high supply voltage and at all times two transistors
Located in the upper part of the circuit is the transistor that conducts at common gate where the input signal is applied to the source terminal and the output is taken from the drain for high frequency gain, low input resistance, high output resistance, and a current gain almost at unity. This configuration can be used as a current buffer or voltage amplifier which is applicable to CMOS RF receivers.
The circuit uses two 2N3819 FET’s in cascode configuration. The lower FET operates in common source mode, while the upper FET, operates in common gate, realising full high frequency gain. The bottom FET is tunable allowing a peak for a particular station.
Visit Here for more.