Sloped L Antenna
A stretch of copper wire can provide excellent performance over a wide frequency range, providing it is long and hung high enough. The ideal length is several wavelenghts, but even a wire of 10-12 metres offers a significant advantage over internal antennas. The receiver chassis must be grounded and the input fed from one end of the antenna with copper wire, so in practice the L shape is often simplified by letting the antenna slope directly towards the receiver.
>> Long wire antenna
Thieking Draht20 preassembled wire antenna.
T and Dipole Antenna
Two equal lengths of copper wire can form a dipole anten-
na. A dipole resonates at a wavelength roughly twice its total length, and the mid points connect with a balanced verti-
cal feeder to opposite receiver terminals. A T antenna looks similar, but the feeder wires are shorted and the dipole forms a top capacitance with the feeder acting as the anten-
na and a ground electrode as counterpoise. A horizontal dipole may thus be switched to a vertical T antenna.
>> The simple Tee antenna
Yaesu YA-30 2-30 MHz folded broadband dipole kit.
A magnetic balun transformer can match the impedance of a wire, T or dipole antenna to a shielded coaxial cable over a wide frequency range. The balun is placed in the immediate vicinity of the antenna wires, and the coaxial cable prevents pickup of signal interference from electrical equipment on the way to the receiver. A properly designed balun also helps reduce static noise and protects the receiver input by galvanically isolating it from the antenna.
>> Broadband balun
Wellbrook UMB130 0,1-30 MHz universal magnetic balun.
An antenna tuner can provide the best possible impedance match to virtually any piece of wire. The improved perfor-
mance comes at the cost of operating complexity, with at least a frequency range switch and two interacting variable capacitors to adjust the receiv-
er and antenna circuits. Anten-
na tuners for radio listening should cover the full 0,15-30 MHz broadcast range and preferably include a magnetic coupler to ferrite arials for use with portable receivers.
Simple antenna tuner
Thieking & Kock DE-32 0,15-30 MHz antenna tuner.