ONE CHIP AM RADIO RECEIVER CIRCUIT SCHEMATIC DIAGRAM
The MK484 we use is a Japanese copy of the original ZN414. It contains an RF amplifier, active detector and automatic gain control (AGC to improve sensitivity) all in a 3-pin package. The input impedence is typically 4M ohm. It operates over a range of 150kHz to 3MHz. DC supply of 1.1V to 1.8V & 0.3mA current drain makes it ideal for battery operation. The output is typically 40 – 60 mV of audio signal. Optimal AGC is provided by R3 and C2 (see Figure 2). R3 (the AGC resistor) should be in the range 100R to 1.5K. A bandwidth of about 4kHz is achieved.
