Hobbies And Interests
Building the Beam
Several types of lightweight material can be used to build the beam, such as PVC pipe, wood, fishing poles and aluminum tubing. A nonconductive mast will help keep the antenna direction pattern as designed. See References for detailed diagrams and approximate lengths of the driven section and the reflector sections. You can adjust final lengths by tuning for the lowest SWR and a good match for the coax cable connection. A scale up to about any frequency is possible, although actual physical size may impose limitations.
Insulate the front and rear sections of the beam from each other. To orient the beam toward your station of interest, point it 90 degrees to the parallel supports, not off the end like is done with Yagi and TV antennas.
Description
The antenna's driven section is basically a stand-alone quarter wave vertical with other supporting verticals on each side connected to each other independent of the center vertical. This acts as the driven element in a two-element beam. The antenna is 81 inches at 2 meters. Rear elements are longer than vertical elements on the front side. All three elements are connected together. Front elements are all the same size, and like most beams, the reflectors are slightly larger.
The two-element Bobtail Beam is quite broad banded and easily tuned to 50 ohm coax for the best match. The Bobtail Beam is fed by an air choke of 6 or 7 turns of feed line coax wrapped around a nonconductive form (such as PVC pipe). Connect one end to the feed point on the beam and other end to your transmitter. Install it at the center vertical radiator.