160 and 80m coax loop antenna and coupler
This loop may be your answer. Instead of a variable capacitor at the top there's two at the bottom. These tune the loop to resonance and
provide transformation to 50 ohm. Another bonus is that because there is no rigid structure the loop can be rolled up, making it easier to transport.
Not only that but you can use the coaxial cable for other purposes once you've finished using it as an antenna. And its lightness means you can
support this antenna on a tree branch.
160 and 80m operation
These videos describe the matching box and give an on-air demonstration.
I tried this approach on 40 - 20 metres but results proved disappointing.
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