Folded Dipoles

I have used folded dipoles both in yagis and in wire antennas.

For yagis the advantage is that it is possible to adapt any real impedance playing with the diameters of the two pipes and with the distance.

The ARRL Antenna Radio Handbook used to have a diagram for dimensioning folded dipoles.

For wire antennas there are the following advantages:

· Wide band  (useful in 40m and much in 80m)

· Balanced feeder line (here in Paraguay the 300 Ohm TV flat cable is cheap and available everywhere, the coaxial cable is expensive and available only in the capital and quoted in dollars)

· Balun inside: no need for weather protection. Just a meter of coax between the balun and the transceiver.

· Balun 4:1 is simpler than a 1:1 one.

· Short Circuit at lower frequencies: less interference from MW broadcast.

· Easily grounded: at the balun side or at the radiator side in the centre of the radiator.

· Increased efficiency: the Ohmic resistance is doubled respect to an open dipole, but impedance is multiplied by four. This can be effective on 160m band.

Examples:

My 80m band folded dipole  has the two arms 18.40m long and the spacing is 75cm.

SWR is 1.4 both at 3.5 and 3.8 MHz

My 40m band dipole has the arms 9.5m long an the spacing is 40cm. It has a useful band of 600 KHz.