I'm building multiple antennas tuned to different amateur bands and would like them connected to my SDR for remote listening and analysis, and a handheld radio for transmission, which I may upgrade or supplement with another radio.

How do I build a solid state setup where I don't have to decouple antennas as I shift to a different frequency. Is there an equivalent of an ON-OFF switch that I can trigger remotely?


You're looking for an antenna switch. There are many different kinds of switches available. Manual switches are the simplest and the cheapest, but they allow for the operator to make the common error of having the wrong antenna (or no antenna) connected, which can lead to equipment damage in some scenarios.

If you want a more automatic setup, then you'll want a system that uses relays to switch antennas. Prices vary widely depending on the features that you want: number of coaxial connections, maximum frequency, power limit, amount of isolation (cross-talk can be a problem for some), rated for outdoor use or not, and so on.

The next problem to be solved is how to switch antennas automatically. Generally some software on a computer connected to the radio, or the radio firmware itself, switches antennas based on what the operator is doing. The antenna switch is connected to the computer or the radio, of course. Commercial ham radio rig control software such as Ham Radio Deluxe can be programmed to switch antennas based on the band selected by the operator. If the software that you use with your SDR can do that also, great; if not, you might have to write your own software.

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    $\begingroup$ Also take care to not transmit on one antenna while a receiver is connected to same antenna or to a nearby antenna. $\endgroup$ – Jim Mar 14 '19 at 19:18

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