Thursday, March 3, 2011

The Multee Antenna


Two-band operation in limited space may be obtained with the multee antenna. The portion identified as H should remain as vertical as possible, as it does the radiating on the lower frequency band.

Two-band operation may be obtained on 1.8/3.5 MHz or on 3.5/7 MHz within the confines of
the average city lot by using the multee antenna shown in Fig. Dimensions are given for either pair of bands in the drawing.  If built for the lower frequencies, the top portion will do little radiating on 1.8 MHz; it acts merely as top loading for the 52-foot vertical section. On 3.5 MHz, the horizontal portion radiates and the vertical section acts as a matching stub to transform the high feed-point impedance to the coaxial cable impedance.

Since the antenna must work against ground on its lower frequency band, it is necessary to install a good ground system. Minimum requirements in this regard would include 20 radials, each 55 to 60 feet long for the 1.8/3.5-MHz version, or half that for the 3.5/7-MHz version. If not much area is available for the radial system, wires as short as 25 feet long (12 feet for 3.5/7-MHz) may be used if many are installed, but some reduction in efficiency will result.With suitable corrections in length to account for the velocity factor, 300-Ω TV twin-lead may be substituted for the open wire.  .

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