Quote:
Originally Posted by Radio
OK, so I'm having a brain f@rt.
I'm making up a 40m copper wire dipole with a 1:1 balun fed with ordinary 50 ohm coax. Now using a tuner, I should be able to get on 40m, 20m, 15m and 10m with reasonable SWR.
Right?
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You can get a good match with a tuner, but that does not mean it will work efficiently ! A 40 meter resonant dipole is about 85% efficient on 40 meter, but by using a tuner to get a match to fool the radio, the efficiency drops to about 10% due to the losses in the coax and the tuner caused by a very high swr still present on the coax. You would be far better off not using coax and use balanced feedline that is not effected by high swr like coax is. That 40 meter dipole fed with 300 ohm or 450 ohm balanced feedline would be around 90% efficient on 40, 30, 20, 17, 15, 12, and 10 meters but would need the tuner to do so ! Plus it would have more gain as you move up in frequency since it will be longer than a half wave on the higher bands. Now you could also feed it off center with a 4:1 current balun and get 40, 20, and 10 meters without a tuner. Just make one side around 22 feet long and the other about 44 feet long. This is called an Off Center Fed Dipole and by moving the feedpoint off center the feed impedance stays around 200 ohms where you use a 4:1 balun to convert it down to 50 ohms.