Graham’s talk described a versatile multi-band HF antenna which doesn’t need an ATU and which is efficient and can be used on any or all of the HF bands. It was originally designed by W6RCA and further developed by W5DXP *.

He explained that it relies on the simple notion that the impedance at the end of a length of 450 Ohm ladder line depends on the length of the line, when used with a dipole which is a 1/2 wavelength or longer on the band of interest.

Graham demonstrated how you can simply add or remove sections of 450 Ohm line to ensure that a 50 Ohm impedance exists at the connection end, for any band.

Graham’s live demo used a 1:10 scale model of an 80m inverted vee dipole, fed with 450 Ohm ladder line.

He connected that to a length of 50 Ohm coax, through a 1:1 balun or current choke.

Graham demonstrated how the SWR dips could be moved up or down in frequency, by placing shorter or longer lengths of 450 Ohm feeder in the line.

Graham also demonstrated that the extra length of feeder can be conveniently coiled for compactness, with little effect on its operation at the frequency of interest.

This was demonstrated on the projector using a RigExpert antenna analyser and AntScope graphing software.

At the end of the talk, Graham also briefly introduced the 1/2 wave controlled-feeder-radiation vertical dipole, which he recently made and installed for Victor G3JNB for use on 10m, so that Victor could benefit from the excellent propagation we are currently enjoying on that band.  The CFR vertical needs no radials, so is ideal where you want an antenna with little visual impact and good DX performance, which were Victor’s key requirements.  The antenna is also known as the flower pot antenna and VK1NAM wrote an article on his experience with it #.

* [ The W5DXP Antenna – Details ]
# [ Controlled-Feeder-Radiation dipole ]