New LO synthesizers

The network analyzer required two local oscillators, easily implementable by phase locking a VCO module. However, having already worked with the ADF4350 chips, it made sense to use them. Well, it made sense to use the modules I already had, but I made new boards for them anyway, simpler and with some mistakes corrected. These are four layer boards as the synthesizer chip loop filter routing needed some shielding not possible with a two layer board.

One of the boards contained a buffer amplifier with a +16dBm output and a mixer, implementing the second downconverter of the analyzer receive path. The mixer covers an RF range of 1.5-4.5GHz, while the synthesizer covers 137MHz-4.4GHz, making the converter generally usable.

The other synthesizer uses the same board, with a difference of a couple of components. The mixer and the amplifier are left out and the RF path routed to a different connector, giving about +6dBm of output to be attenuated and fed to the transmit path mixer.

Both boards also contain a tiny PIC10F206 microcontroller to initialize the synthesizer without needing a separate SPI bus from the system main computer. SPI routing is somewhat difficult, as the computer board only has a few chip select lines. Increasing the number of possible SPI slaves would require a redraw of the interface board with some more thought for the SPI control.

The resulting boards. They will probably require some more supply filtering and perhaps some shielding to improve signal quality. The GPS reference output also seems to require some more work.