The GM4JMU Shortened 7Mhz Dipole
To construct each side of the antenna proceed as follows. Cut a 10.25
metre length of 24/0.076 insulated wire, and a 160 mm length of 40 mm o.d
plastic tubing ( white plumbers tubing). Measure a 2.75 portion of the
wire and attach the wire to the plastic former. Wind 40 turns of the wire
onto the plastic former, and firmly secure the end of the winding. Make
the other half of the antenna in the same way. Attach the ends of the 2.57
metre sections to a suitable centre insulator, which should also mount
the choke balun, connect the 50 ohm coax, then carefully waterproof the
The choke balun uses RG174AU coax and a 40mm Ferrite Toriod.
Once the antenna is errected adjust it to resonance on 7.030Mhz
by folding back the ends, and adjust the length to provide minimum SWR.
Article from SPRAT Issue 74 Spring 1993