FM Exciter

 

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The main components that consist and Exciter for FM (87,5MHz~108MHz) radio band are the following:

  • Power supply. The unit that provides the correct voltage to all circuits: digital, analog, RF. Our unit is capable to provide filtered fixed voltage for digital and analog modules,variable voltage for RF power modules (in order to be able to control the transmitting power) and also protection for automated  RF power switch-off (ie over current conditions, increased SWR).
  • Voltage Control Oscillator (VCO). The most important module of the Exciter, responsible to generate the central frequency – in the FM radio band – and modulate it depending on the input-audio voltage.
  • The Phase Locked Loop (PLL) unit. The unit controlling the input voltage of the VCO and monitoring the phase in order to keep the frequency stable. Our unit is digitally controlled using an MCS51 family controller.

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  • Power amplifiers. We are using 3 stages of amplification. The first is 3 Watts then 15 Watts and the final step outputs 120 Watts.

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Digital PLL Design

Our PLL Frequency Synthesizer is based on Philips UMA1014 Digital PLL, controlled through I2C bus interface. The PLL is controlled by an AT89C52 ATMEL microelectronic that is also equipped with a LCD display and a 3×4 keyboard. The user is able to select the PLL frequency, check the system status – such as the temperature, lock the configuration functionalities using a code and also set the protection level.

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PLL unit schematic diagram