Build a 7 Element 4M (70MHz) Beam
By Paul Graver, M1CCZ

The 4m or 70Mhz band is not an allocation that is in widespread use, consequently the bulk of the equipment for this band has to be homemade. In the UK the band extends from 70.00 to 70.50, this 7 element beam, designed around a centre frequency of 70.25 provides approximately 12dBi gain with a F/B ratio of 30dB.

All of the elements are 13mm diameter aluminium tube mounted through a 50mm diameter aluminium boom, including the driven element, which is not split or insulated from the boom. The overall boom length is about 5 1/2 metres. To match the beam to the 50 ohm feeder, a Delta Match arrangement is used.

Element    Length    Spacing
Reflector    2198        778
Driven        2106
Director 1  2023        540
Director 2  1924        885
Director 3  1921        755
Director 4  1928      1110
Director 5  1797      1260
All dimensions in millimetres

Above: Theoretical Radiation Pattern Below: VSWR, F/B Ratio and Gain