Most amateurs have used coax switches for switching one transceiver between multiple antennas or having the one antenna going to multiple transceivers.
That's fine for coaxial feedline but what about open wire line? Sometimes you need to switch in an extra length of feedline to assist impedance matching. You may have two dipoles fed with open wire feedline, perhaps oriented differently. Or, you could be experimenting with switchable direction open wire-fed beams where again you may be switching balanced line.
A knife switch can help. Immortalised by Frankenstein, they've been around since the early days of human harnessed electricity. I've seen cheap ones on eBay but their quality may not be good. You could be lucky and find an old one at a hamfest. Making your own is another option. If the latter appeals, here are some ideas:
* Instructables knife switch
* Instructables knife switch
PS: Returning to amateur radio? This book can help fill in what you've missed. Available for $US5 as an ebook with a paperback version also available, this will bring you up to speed in no time. Available via Amazon, you can find out more here.
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