Ham Radio Technical Discussion Net: VU3MJL Shares Experience with Loaded Coil Fan Dipole

 Today's discussion on  Ham Radio Technical Discussion Net on 7065 kHz, 1:45 am UTC (7.15 am IST) was centered on Loaded Coil Dipole Antenna. VU3MJL shared his experience with a loaded coil dipole which he had loaned from a friend and tried way back in February. He had very little space on top of his apartment. That was why he opted for a loaded coil dipole as an electrically shortened dipole. Loading coil cancels the capacitive reactance of an electrically short antenna which is less than half wavelength. The antenna which he tried was a fan dipole with spacers between elements for 40m, 20m and 10m amateur radio bands. 20m and 10m elements were not coil loaded, while 40m antenna had a coil on either side near its end. There was a small length of the 40m element beyond the coil as well. He had to use 50m long RG58 coax to connect the antenna to his radio. Whether it was the loss in the cable or in the loading coil, he could not have a single contact with that antenna and he returned it to his friend.

Though the experience of VU3MJL was the worst case scenario, loaded coil dipoles are being used by others when a shortened dipole is needed. A very compromised mounting and long cable could have resulted in the poor performance in his case. Location in a city with heavy RF noise would have been other reason why he could not hear other stations well with that antenna. The resistive loss induced by the loading coil could diminish the intensity of received signal to have it below the noise level in a city environment. In a rural setup with clearance around, and lower background noise, the same antenna could have given a better performance. The antenna had a 1:1 balun also. Some say that even the balun could cause some drop in signals, though a balun is ideally needed while feeding a balanced antenna like a half wave dipole antenna with an unbalanced feedline like a coaxial cable.

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73 de Jon, VU2JO