Mini Qua Loops

Three-fifths-size loops with full-size performance by Dean FrazierNH6XK

Eventually a ham discovers the gain, and especially the quieiness on receive,, of loop antennas, and plans to construct one. Soon enough it becomes apparent that loops for the bands beiow 20 meters arc impossibly large. A square loop on 40 meters (7.15 MH/i. for example, needs sides about 35 feet long, which may be unreasonably large to erect, especially in the vertical plane. However, a loop, or any antenna, can be made physically smaller while maintaining lull electrical size, Hi is can be accomplished with loading coils, as is frequently done in mobile applications. Unfortunately, coils do introduce some loss. Another approach is to reduce the size of an antenna, e.g. cause it to be resonant above the desired frequency by mechanical shrinking, and then capaciiively "stretch11 it. so as to achieve the proper electrical length ior resonance. 'Hie latter is the approach taken here.

The mini-quad loops described are not quite three-fifths full size, and yet, via capacitive loading, are electrically stretched to a full wave. We don't get something (size reduction) for nothing, however. We do suffer some reduction in bandwidth, and we lose about 12 dB compared to the performance of a full-size loop. The former limitation may only be a problem on the higher frequencies, lor which bands a mini-quad loop can be tailored for a specific portion of the band. Note that the 2; I SWR bandwidth on 12 and 17 meters (Table I) and 30 meters is greater than the entire width of the band. Regarding the second limitation. recall that a very good human ear just might detect a I dB difference in received signal. . . clearly a 1/2 dB reduction with a mini-

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