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It probably won't be as easy as that, but that's the idea in general. The idea is just a simple Wheatstone bridge, and the potentiometer being the antenna. When the antenna is unmatched, the bridge is unbalanced and a potential difference is developed, which is !filtered! and then ran through a uA meter. The uA meter should be at least 15uA or so, and all resistors should be rated 1W or more. The switch switches between 50Ohm and 75ohm antenna impedance, to choose from. When perfectly matched no current should flow through the uA meter. Try matching it.
P.S. This is far from perfect, and i wouldn't really recommend it, but if you're a radio hobbyist and can't get your hands on a real SWR meter, this oughta do the trick. As the headline says, this is a Poor Man's SWR Meter. The parts can be salvaged from almost any circuit. The 10pF capacitors should be 470pF or even 1nF. The recommended input power level is 1W and above (20Vpk-pk in 50ohm). At high frequencies it's important to keep some layout rules, in order for it to work reliably. For instance, keep all leads short, use screening, use only carbon resistors and not wirewound. Keep any source of parasitic influence away, and use completely matched resistors. The tolerance should be 1% maximum. Measure a bunch of resistors and use the closest in parameters. This is really important for best results.
P.P.S. The uA meter should be digital because if the antenna is unmatched in one direction, the current flow will be in reverse to the uA meter's polarity, thus not indicating anything, or even breaking the meter. A digital ammeter can have its polarity reversed and will still give a reliable reading
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