In my thesis work I have desiged an upconverter circuit for the USRP (Universal Software Radio Peripheral) for the 400-860 MHz frequency band. There are several up- and downconverter daughterboards in the market for the USRP, the simplest are the BasicTX and BasicRX. These boards do not contain up- and downconverter blocks, so they can be used only in low frequency applications. The upper limit of the usable frequency range is constrained by the analog-digital and digital-analog converters upper marginal frequency. They are mainly designed to be acquainted with the USRP basic functions. Besides these daughterboards the users could buy other boards which structure is more complex. These could operate in a wide or a narrower specified frequency range. We do not find a daughterboard on the market which is designed solely for the VHF frequency band. We cannot use the boards which are proposed for universal application to do accurate measurement tasks. Engineers have to make trade-offs between the wide operating frequency band and the accuracy when they design a comprehensively usable board.
The parameters of my daughterboard are set by the requirements of the university department. It needs to be able to work in the 433MHz HAM radio frequency band, and the upper frequency limit has to be the top of the VHF TV band. The board has to contain an amplifier block for the higher output power.
After specifying the assignment I analized similar existing daughterboards. These boards are the RFX400 and the WBX, they gave me basic information on how to chose the appropriate ICs and how to design a proprietary daughterboard. The next job was to investigate the chosen IC’s datasheets. Beside the technical description these documents gave useful information by the demonstration circuits to help designing my own circuit. I made a comparison between the demonstration circuits and the circuitry of the RFX400 and WBX.
I designed the electrical circuit diagram and the PCB by Altium Designer. I was particularly paying attention to separate the parts of the high frequency components of the circuit and to modify the footprints to account for the manual soldering process. When the PCB was finished, the remaining job was the population of the board, the measurement of the functional blocks and the fixing of the remaining flaws in the design.