1 MOSFET RF/IF Amplifier

The diagram to the right shows a single stage MOSFET tuned amplifier which may be used as a preamplifier, RF or IF amplifier. Depending on the frequency of operation, the gain will be from 15dB to 30dB - higher gain at lower frequencies.

Decoupling values are typical for operation on the HF bands.

Two bias options are shown - use A if AGC is not required and B if AGC is required. The no-signal AGC bias should be around 3-4V.

For low impedance applications, the turns ratio of T1 and T2 will typically be between 5:1 and 10:1. The capacitors used for high impedance coupling applications will typically be significantly less than the values of the tuning capacitors C1 and C2.

The MOSFET may be a 40673 (if available) or a more modern device like the BF960. IF a UHF device is used at lower frequencies then any tendency to UHF oscillation may be stopped with a ferrite bead between the drain and the primary of T2.

2 MOSFET Mixer

The diagram to the right shows a single stage MOSFET tuned mixer. Depending on the frequency of operation, the gain will be from 10dB to 20dB - higher gain at lower frequencies.

Decoupling values are typical for operation on the HF bands.

AGC should not be applied to this type of circuit.

Oscillator injection should be 4v peak-peak.