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The W1DTV top-loaded delta loop
On 80- and 160-meter bands, height limitations can reduce the effectiveness of the delta loop. The objective of the loading is to "lift" the current nodes higher in the vertical space available for the antenna. The loading stub must be horizontal but this is rarely possible. It should be around 9.8 meters (32') at 3.825 MHz. However, Frank J. Witt, W1DTV, had to lengthen it to 13 meters (43') for resonance when the wire makes about 60-degree angle with the plane of the loop. The stub could be shorted by means of a loading coil installed in series with the stub at the point where it is connected to the triangle apex. The 13-meter wire was reduced to 4.9 metres (16') by the use of a 32µH loading coil but it results in a reduction of antenna bandwidth.
Use a quarter-wave 75-ohm coax cable between the feedpoint and the 50-ohm transmission line. It is desirable to have a balun to prevent antenna currents on the coax feedline.
 
The G4ZU miniloop
Dick Bird, G4ZU, has developed a compact loop antenna that will appeal to those with limited antenna space. Dick felt the loop could be scaled down in size until the feedpoint resistance was about 50 ohms without the bandwidth becoming excessively narrow. He decided to fold the wires back in such fashion as to retain the total length of wire in the loop but accomplish an appreciable size reduction. The portion of the loop folded into a transmission line can be adjusted slightly by trimming the length untill the minimum SWR falls at your chosen frequency. The feedline spacing is not critical: four to six inches will do the job. The radiation of the "Miniloop" is bidirectional, like a dipole, with good nulls off the side.
 
The WBØAOF 80 meter pyramid antenna 
William R. Mest, WBØAOF, has tried numerous types of antenna systems on 80 meters but the pyramid antenna is, by far, the best system he has found for him. It actually looks like two delta loops, about the size of 40 meter loops, sloping in opposite directions. The entire wire length of the antenna is a full wavelength in a configuration that is doubled back on itself, then sloping in opposite directions. As can be seen, the wire crosses itselfs at the midpoint of the antenna. In the original article, the author chose 75-ohm coax but he stayed away from this direct feed system and used a quarter-wave 75-ohm coax cable: this pyramid antenna exhibits a characteristic impedance of about 90 ohms.
Keep in mind that a unilateral triangle is not absolutely necessary to make this antenna work but the height of the horizontal sections above ground should be a minimum of 10 feet.
Radiation is mainly off the slanting wires: at lower angles, radiation is strongest in the direction A-B, weakest in C-D. In other words, the antenna is great for short distance contacts and very good for DX contacts.

 

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