This work describes the design of a radio-frequency source, based on fractional phase-locked loop signal synthesis in the range of 34.375MHz to 4400MHz. With the addition of an adjustable attenuator to the RF source, we obtain a practical instrument that can be used in the development and testing of radio components and networks.
The introductory part describes the design of the instrument with the selected components. Followed by a brief description of the theoretical signal synthesis formulas, using fractional phase-locked loop in the case of the ADF4351 integrated circuit.
The second part describes the practical implementation of all the constituent blocks of the instrument with the electrical plans, measurement characteristics and concludes with a description of the most important parts of the software code that control the instrument. ADF4351 is powered by ADP150 and LM1117 regulators. The synthesized signal travels through the balun made of ferrite rings, to the MMIC amplifier Gali5 + and from there, to the circuit of the attenuator. The attenuator is made of two HMC307s, connected in series, which are controlled by two 4053 multiplexers and a serial-parallel shift register 74HC595. The HMC307 and 4053 need a negative voltage supply, for their operation, which is provided by the LM828 inverter. The shift register is controlled by a microcontroller, which receives commands via the four keys on the LCD screen. The instrument is powered by the voltage regulator RC1587M that converts an external voltage of + 12V to + 5V. The software code provides a better user experience, accurate instrument calibration and verification of operation code via the serial bus.
The final section describes some limitations of the ADF4351 and ideas for improvement, and the results of measurements of the output power of the carrier.