This is an idea for a rapidly erected field antenna with a single mast supporting 3 or 4 sloping dipoles. The dipoles act as the guys. Conceivably, one can switch them in and out to get some directivity, particularly if you were to switch some sort of impedance in at the feed points to make them shorter or longer electrically. The other idea is to put a switchable feed at the top, which, if you short the feed point in the middle of the dipole, makes it into an inverted V. This might make a practical multiband antenna, although, I don't know that there is any real radiation efficiency advantage in a inverted V over an electrically short sloped dipole. (Later comment (Dec '02): I suspect that the inverted V might work better, because the high current part of the antenna (near the feed) is higher above the ground)
I'm going to assume a 10 meter high mast, and elements that are about 10 meters long, sloped out at 30 degrees (i.e. 5 meters away from the tower at the bottom.
Here's a NEC model file
CM Quad sloping dipole design sheet CM CM Center Tower Height 10 m CM Dipole Length 10 m CM Angle from vertical 30 deg 0.523598776 rad 0.5 0.866025404 CM Deflection from vertical 5 m CM Height of lower ends 1.339745962 m CM Top hub width 0.1 m CMGW,900,101,0,0, 0.000,0,0,10,0.025 CE seg nseg x y z x y z GW,101,101,-5,0,1.340,-0.05,0,10,0.001 GW,102,101,5,0,1.340,0.05,0,10,0.001 GW,103,101,0,-5,1.340,0,-0.05,10,0.001 GW,104,101,0,5, 1.340,0,0.05,10,0.001 GE EK GN,0,0,0,0,4,.001 EX,0,101,51,0,1,0 PT,-1 FR,0,10,0,0,13.8,0.1 XQ EN
radio/antenna/quadsloper.htm - 26 Aug 2002 - Jim
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