The technique to match the natural 300 ohm impedance of a folded dipole to 50 ohms simply uses matching section of an electrical 1/4 wavelength of 125 ohm coax (RG-63B). It is usually installing inside the dipole in order to be able to weatherproof the dipole easily at the feedpoint but I imagine it could be installed external as well. I have a page with a pictorial of the design I used some years ago. I made a number of arrays for VHF and 220 MHz using this design some time ago.
http://www.gorum.ca/sinc_ant.html (ignore the links at the bottom - I didn't finish the web page set) RG-63B is very hard to find and it is not cheap ($3/ft) but I do have a quantity left over from when I was making the dipoles 15-20 years ago. Burt VE2BMQ wd4nmq_1 wrote: > I am looking at building a 2M four bay antenna, But, I have a > question > > My question is the design and construction of folded dipole antennas > used as individual elements in bay type antennas. In doing research > into their construction I came upon a catch. All design info I found > in books, ARRL Antenna Book, etc, says a two element folded dipole > has a nominal input impedance of 300 ohms. But, all sources, DB > Products, Benelec, etc, I see say the nominal input impedance for > each folded dipole element is 50 ohms, 300. I reference WB2EDV's > article on a 440 antenna he built. > > But, the bottom line is can anybody point me to where I can find the > info on designing each element for 50 ohm impedance? > > Jeff wd4nmq
