HF Antenna Switch
A remote antenna switch built to be driven automatically by the band decoder — and built on a ground-plane PCB inside a shielded aluminium enclosure, so isolation between ports holds up at real HF power levels.
Overview
This switch exists to take antenna selection out of the operator's hands entirely: paired with the band decoder, it switches automatically the moment the radio changes band, with no extra cable run beyond what the decoder already taps into.
Because it's switching live RF rather than just logic signals, the build leans hard on the PCB layout and the enclosure: a solid ground plane under the relay traces, careful copper pour, and an aluminium case that actually shields one port from the next — rather than just keeping the weather out.
Measuring port isolation
Isolation between ports was measured directly on a NanoVNA rather than assumed from the schematic. That measurement procedure has its own quirks worth knowing if you're repeating it: the VNA's dynamic range sets a hard floor on how much isolation you can actually resolve, and connecting a real, resonant antenna to one port during a cable-loss measurement will invalidate the result — the antenna itself becomes part of what you're measuring, not a passive load.