“Playing around with SDRs for more than 14 years now, I learnt a lot. Not on a very professional level, but on a hobbyist niveau.
I went through developing some firmware for the CY7C68013A, a framework for transferring IQ data from SDRs to processing modules, implemented a spectrum analzer UI, demodulators for all kinds of protocols like GSM or POCSAG, etc etc.
But apart from building cables I never was tinkering with the RF path itself. Neither do I have an amateur radio license, nor did I really design RF hardware. The latter is something I wanted to change and finally did.
Recently I built a 405 MHz tuned ground plane antenna for weather balloon tracking using the rdzsonde ESP32 firmware. Later I added a 6 m long copper tape dipole antenna for the other bands. Having some antennas in my attic now, I wanted a comfortable solution to switch between them.
Of course I have choosen an ESP32 for the brain, switching multiple antenna inputs between two outputs. This and a WS2812 for the obligatory RGB colors.
I had the idea to use one MXD8636 SP3T switch per input channel to choose between two RF outputs or a 50 Ω termination.
As this switch also has an open position, it is also possible to disconnect the antenna with 25-35 dB isolation. Guess that value is quite okay.
While the switch is quite good with only less than a dB insertion loss, I still placed a switchable 17 dB amplifier using the AD8354. I was not sure if I ever would need this as Tx switcher, so I made the amp completely bypassable using two switches – before and after the amp. The switches I used for that are MXD8625C SPDT in a microscopic 1.1 mm x 0.7mm 6-lead QFN package. Hell is that package small.”