Vertical loop antenna (LOOP)
According to my observations, the antenna is the "Windom" is rarely used by Amateurs. However, due to the lack of notch filters and the possibility of asymmetric power, it has some advantages in multi-band mode. Besides, it is quite simple to mount. And only for operation in the range of 160 m, it is too short. In this note proposes a possible exit.
For example, if we want to use FD-4 (the most famous of this type of antennas) on 160 m, the lengths of both arms are doubled, the antenna becomes too long. The only way is to fold the lengthening of the emitters, so that in itself results in a vertical Loop antenna. However, for 160 m. this loop must remain open.
Thus we have a closed vertical loop for all classic Amateur bands.
As can be seen in the results of many experiments, the form covered by the antenna area is not important. Setting does not pose problems, but for 80 meters, you need to connect the capacitor, which is not needed at higher ranges. With this capacitor can 80 m to shift the resonance to where it is needed. The best was the condenser 160 pF. I made it out of the foil fiberglass 1.5 mm thick, the area was h mm Capacitor can withstand the power of 750 watts. For operation on 160 meters it is necessary to short-circuit and disconnection of the loop to attach to a running relay contact additional tuning wire that can be hung zigzag at low altitude.
The top wire should be hanging at a height of about 13m, otherwise difficulties with the placement of the extra wires at the bottom. The lower wire at that hangs over the earth at a height of about 3 m, except in the range 3.5...3,55 MHz, where the SWR was received about 2.5, all the other bands he has been in the range of 1.1...2. Of course, at the highest ranges of the antenna is much more broadband.
Author: H. SARRASCH (DJ7RC). Translated By A. Belsky; Publication: N. Bolshakov, rf.atnn.ru