A folded dipole made from 300 ohm twin lead will have an input impedance of 300 ohms. So, feeding it with 50 ohm coax is going to leave you with a high SWR, 6:1 or more. You could always use a balun to transform that 300 ohms to 50 ohms. If you also used 300 ohm twin lead for the feed line you could put that balun at the bottom end, near the radio. Same thing except a bit easier to deal with. Or, just use a tuner with a balun in it and run the twin lead straight to the tuner. If you are planning on using it on more than one band you are going to need that tuner anyway.
There would be no particular benefit in use a folded dipole such as that, it is not any more 'broad-banded' that a dipole made of single conductor wire. The diameter of the conductor making up an antenna does have some effect on an antenna's broad-bandedness, but you are not talking about fractions of an inch diameter at HF. That gets into the multi-inch category, as in a foot or more, before that broad-bandedness ever shows up to any significant degree. Even so, you'll still need that tuner for multi-band use. Since you are going to ahve to have one anyway, why not get one that will handle more than you'll probably ever need. Look at the big ones, not the little ones. The smaller they are the less voltage they can handle. Any impedance transformation of any 'size' means higher voltages. The ratings of tuners are always more optimistic than is claimed...
- 'Doc
There would be no particular benefit in use a folded dipole such as that, it is not any more 'broad-banded' that a dipole made of single conductor wire. The diameter of the conductor making up an antenna does have some effect on an antenna's broad-bandedness, but you are not talking about fractions of an inch diameter at HF. That gets into the multi-inch category, as in a foot or more, before that broad-bandedness ever shows up to any significant degree. Even so, you'll still need that tuner for multi-band use. Since you are going to ahve to have one anyway, why not get one that will handle more than you'll probably ever need. Look at the big ones, not the little ones. The smaller they are the less voltage they can handle. Any impedance transformation of any 'size' means higher voltages. The ratings of tuners are always more optimistic than is claimed...
- 'Doc
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