This is a circuit for a high performance RF amplifier for the FM band which can be successfully built without any special test equipment. The output transformer is designed to resonate with the FET's drain capacitance at about 92 MHz giving the amplifier the highest gain at the low end of the band where the weaker stations operate. This is the figure of the circuit;
The performance of the amplifier is quite good. The noise figure is below 2 dB and the gain is over 12dB. The low noise figure and good gain will help car radios or home stereo receivers pick up those weak distant stations or the lower power "talk radio" and university stations. FM receivers loose signals abruptly so if your favorite station fades in and out as you drive, this amplifier can have a dramatic effect.
The coil is wound on a section of an ordinary pen cap. Find a ball-point or felt-tipped pen with a plastic cap with an outside diameter of 0.4 inches. Cut off a piece 0.6 inches long. Poke small holes 0.1 inches from each end to secure the ends of the primary winding. Wind a ten turn primary of solid copper telephone wire around the tube passing each end through the small hole to secure the winding. Any small-gauge insulated wire which nearly covers the tube will work but the common telephone cables (which typically contain 25 colorful twisted pairs) yield excellent prototyping wire. The secondary is two turns wound around the ten turns.
The performance of the amplifier is quite good. The noise figure is below 2 dB and the gain is over 12dB. The low noise figure and good gain will help car radios or home stereo receivers pick up those weak distant stations or the lower power "talk radio" and university stations. FM receivers loose signals abruptly so if your favorite station fades in and out as you drive, this amplifier can have a dramatic effect.
The coil is wound on a section of an ordinary pen cap. Find a ball-point or felt-tipped pen with a plastic cap with an outside diameter of 0.4 inches. Cut off a piece 0.6 inches long. Poke small holes 0.1 inches from each end to secure the ends of the primary winding. Wind a ten turn primary of solid copper telephone wire around the tube passing each end through the small hole to secure the winding. Any small-gauge insulated wire which nearly covers the tube will work but the common telephone cables (which typically contain 25 colorful twisted pairs) yield excellent prototyping wire. The secondary is two turns wound around the ten turns.
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