VHF Receiver Using Single Chip

The project was based on the KA22429 that is equivalent to a TDA7021 to create a small and cheap FM receiver.

The microchip used in this circuit came from the family Philips TDA7000. Two application notes can be obtained from the site of Philips. This will explain how this chips work which includes an application note for the narrowband FM operation. The TDA7021 was easy to move higher up into the VHF band that covers up to more than 160MHz.

There are other chips such as TDA7088 that includes clones such as SC1088, CD7088, and D7088. The TDA7088 supports single button tuning which allows a scan-and-stop function at available channels with a reset button to start the search over at the low end of the radio band. Across an external varicap diode, an internal circuit of the TDA7088 generates a ramp voltage. This changes the capacitance in proportion to reverse diode bias to affect tuning.

The TDA7021 is a 16-pin surface mount device with an FM receiver with a 76kHz intermediate frequency. This receiver uses the headphone cable as the antenna and there is a coupling capacitor which is connected to headphone socket.

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