With the apex at 27meters (!), this vertical deltaloop is an interesting alternative to the quarter wave vertical I have been using most of the winters. Main reason for trying out this antenna, is the fact that it doesn't require any ground system/radials. A great advantage in my situation, where most of the antenna's are deployed in a farm field during the winter, but all must be removable within 24 hours upon notice. The loop is strictly equilateral, all three sides measuring 1/3Lamba, which at 3.8Mc equals 26.32meters. The feedpoint is located at precisely .25Lambda (19.74 meters) from the top. Feeding the loop at this point gives maximum suppression of NVIS-signals. I made this loop using 1.6mm aluminium wire: cheap, light and very strong. Two disadvantages: can not be soldered, and kinks very easily.
photo 1: the loop, apex at 27 meters
photo 2: the tower carrying the wire deltaloop
photo 3: yet another photo of the loop. Note the black top-section, being a spare mast from a surfboard ;)
photo 4: professional self-clamping guy-wires
Measuring the loop's parameters
Using the AIM4170 the following plots could be made.As can be seen, the loop is resonant at 3.807Mc, which is very close to the calculated value of 3.8Mc?!
The impedance at the resonant frequency is roughly 150Ohms.
Modelling the loop using 4NEC2
To get a better feeling for this antenna, I also modelled it using the great 4NEC2 program of Arie Voors, check it out at http://home.ict.nl/~arivoors/.
Here are some screenshots you may find interesting:
figure 1: wire model 80m vertical deltaloop
figure 2: vertical radiation pattern - this is a DX-performer!
figure 3: 3D radiation pattern
figure 4: impedance plot (based on model!)