The internal oscillator may be reluctant to operate below 1 MHz. Of course, if the external oscillator is employed, a digital frequency readout can also be utilized. The internal oscillator can be disabled and an external oscillator used. It features an on-board oscillator, capable of up to 200 MHz or so, and provides about 18-dB conversion gain. The AN602 mixer, designed for use with cellular phones with a frequency response in excess of 500 MHz, takes care of all this.
It also must have a low noise figure that isn’t adversely affected by the oscillator injection power level.
Af filter superhet full#
Power-supply requirements are 9 to 12 volts dc at 10 mA average (up to 30 mA at full volume).Ī good mixer design should be very “strong” (i.e., not easily overloaded by strong stations) and it should have significant conversion gain. The receiver is based on the AN602 double-balanced mixer IC, with the big brother of the ZN414 (the 10-transistor radio chip), the ZN416, employed as an IF amplifier, coupled with a standard LM386 audio stage ( Fig. Also, in a conventional set, the tuning capacitor needs at least two gangs, and they must be able to track each other to maintain the sensitivity across the entire reception band. In a conventional superhet design, the antenna coil, as well as the oscillator coil, would need simultaneous adjustments. It also makes the receiver very easy to experiment with by changing the coil dimensions, etc. When constructing a superhet receiver needing just one coil/tuning-capacitor combination, there’s the obvious advantage that only one simple coil needs to be made. The receiver circuitry as presented here can be built for less than $50.ĭon’t be misled-even though the set has some pretty obvious limitations as presented, it’s still capable of worldwide reception when connected to a few meters of wire as an antenna. This idea presents a simple circuit for a superhet radio receiver that can be built up in sections, with each section tested before assembly.
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