This is the most compact broadband doublet I was able to design. Its length is only 6.6 m. The small size of the doublet allows you to assemble it even in a small backyard. The prototype antenna has been sitting on a 9 m tall mast for more than 4 years now, and it has been operating very well indeed.
I described this antenna in a very detailed article published in RadCom 2019/08.
The Multi-Loop Doublet has been made from aluminum tubes and copper stranded wires. Theoretical antenna dimensions are 6.6 x 1.2 x 0.6 m, but you must add some mechanical margins. So, its real dimensions are about 10 cm larger. See the picture below for the dimensions of the aluminum structure.
Antenna under construction.
Antenna construction shown in phases.
SWR plots.
Matching network was built on three 140-61 toroidal ferrite cores. Copper stranded wire in high voltage insulation was used to wind all three transformers. Number of turns: 8.
The prototype antenna performs very well. When compared to the multi-band GP, it always produces stronger signal and has always lower level of background noise. It happens that I can hear a signal on a multi-loop doublet but can not hear it on GP. The vertically polarized antennas are electrically noisy. Multi-loop doublet can replace a multi-dipole (a.k.a. fan dipole), it is smaller and it does not require any trimming.
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P.S. When I was designing this antenna, I had limited knowledge about the ferrite core inductors. Since that time, I have made some progress in that field (see the TFCI calculator) and I would design the transformers differently now. My present recommendation is:
TR1 through TR3 - core: Fair-Rite 43 material, 1.4" O.D. (part number: 5943002701), winding: 10 turns of 2 insulated wires (thick, high voltage insulation), d/D ratio equal to 0.4-0.55, where d is the conductor diameter and D the insulation jacket diameter.