Home-made RF Signal Generator

To begin with, I would love to make a quick summary of the first part of the RF signal generator project. If you are interested in a longer version you can find it here.

I’ve order a PCB from OSHPark for the ADF4355-3 and low noise regulators for supplies and added some gain block to the output to increase the power level of the RF output signal. The final board was 3cmx3cm. It took a long time before PCBs could finally make it here, almost a full month. The programming of PLL will be done from another board with FPGA. In order to simply the soldering process, I’ve also ordered a custom-made stencil for this board.

Soldering the components

The board contains some 0402 package components as well as other hard-to-solder ICs which made it necessary to order a stencil. I’ve placed the stencil over my board and then applied my solder paste using the solder paste spreader gifted by OSHStencils. ┬áThen I’ve pick and placed all the components to where they should be. After that, I’ve soldered them using a reflow oven at our university.

However there were many shorts, almost all of them were caused by some solder bridges. After working a little bit on the board, I’ve realised that the shorts were under ADF4355. Removing ADF4355 from the board solved the issue. Then we’ve decided to build a new board and removed some solder paste before using reflow oven. This time, the result was perfect. The board had only a single short, which took less than several minutes to get rid of. Now, our RF signal generator looks like this.

RF Signal Generator Board

Conclusion

Now begins the programming stage of the PLL to make it function properly. I’ll try to use some cheap MCU, or Arduino to program the PLL. However, in order to make it tunable, a simple Arduino may not be enough. I would love to use some kind of a touchscreen to enter desired frequency of operation. When I would be able to program the board to provide a desired frequency, I’ll test the output of the PLL using a real-time signal analyzer or a spectrum analyzer. Then, I would add a step attenuator and a power detector to keep the power level checked at all times and this way I would have both the output frequency and power level tunable. This way, I would have a fine RF source for my future projects.

Categories: Microwave/RF

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