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