FM PLL Synthesizer PLL circuit clearly smaller than the old one, a result we have added to the radio board, power control circuitry that allows it to activate, the RF signals to detect when a key is established. Even a simple LM317 which supplies RF final stage, which is controlled by a lock detect signal through the ADJ pin. Oscillator and the RF driver stage has been improved to get the harmonics rejection better than previous versions. We have replaced it with a new BB204 varactors: BB209. As a result, kvco more stable on the FM band and AF signal has been directly applied to the channel control voltage coming from the PLL. A Cauer filter has been added to enhance the second harmonic rejection. Digital board 16F84 [16F84_Digital_Board] Board digitally using 16F84 microcontroller to drive the FM transmitter is equipped with MC145170 PLL circuit. Pic is responsible for controlling the SPI bus in order to provide 205 channels of the FM band. Two key allows you to initiate a scan through the FM band frequency with a frequency of 100KHz step and also the storage operation into the EEPROM. When the frequency setting is reached, pic lock control signal to prevent the problem of detecting the radio hardware. This scheme is quite simple, so it is not really necessary to provide technical explanation regarding the design. Lcd screen is * 2 16 characters with backlight. Download Schematic FM Synthesizer (pdf) - Digital Board Schematic (pdf) - Digital Agency Hex.