John,

The most power-efficient antenna which will fit into a loft is the so-called
magnetic loop.

A loop, 2 or 2.5-metres square, or a circular or broad rectangular loop of
the same perimeter, made with 25mm plumbers' copper pipe will work
reasonably well at frequencies as low as the 160m band.

The greater the area enclosed by the loop and the greater the conductor
diameter, the greater the efficiency.

A remotely-controlled, slow-motion, vacuum tuning capacitor (1000pF for
160m) can be expensive. But capacitors rapidly get progressively much
smaller on the 80 and 40m bands, etc. A range of three bands, eg., 80, 40
and 20m, can be covered with one capacitor.

Very high efficiency, comparable with a 1/2-wave dipole can be acheived at
the higher frequencies within a much smaller space.

Whether you make one or purchase one, or just amuse yourself with figures
you can compare performance versus dimensions by downloading program
MAGLOOP4 from website below. Download in a few seconds and run immediately.
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Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
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