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Conventional Off-Center Fed antennas start with the goal of making the antenna work well on the lowest frequency band placing the harmonic resonances high or outside the upper bands usually requiring an antenna tuner on some or all those bands. OCF Masters antennas are longer placing the resonant frequencies of the higher bands well within those bands. Capacitive loads are then used to pull the resonant frequency of the lowest one or two bands up towards the center of those bands. The placement of the capacitors is critical to avoid affecting the resonant frequencies of the upper bands.
A similar approach can be taken with dipoles operating on both a fundamental and third harmonic as with a 40M antenna that also works on 15M. By cutting the antenna to operate at 6.94MHz, it works well on 15M. The antenna’s resonant frequency can be brought up to the middle of the 40M band by placing a capacitor at 1/3rd the length of the antenna.
Capacitors connected to antenna wires are subject to two dangers. The first is static build-up caused by friction and natural electrical activity. A resistor across the capacitor bleeds off any accumulated charge saving the capacitor from electrical breakdown. Additionally, Capacitive loads are subject to high currents and high voltages especially on the lower bands. OCF Masters Loads are built to withstand both hazards. Running more power to the antenna than the Load rating will lead to capacitor and antenna failure.
In order to make building our unique antennas simpler, we have put together the parts that are difficult to obtain, namely the capacitive loads, in load and insulator kits for 160M, 80M and 40M OCFs and 40M/15M dipoles. The kits for each band covers powers up to 800 watts or up to 1,500 watts. The only other components needed are the Balun and wire. For 160M and 40M OCFs, we highly recommend using our Balun kits as they have higher transmission line isolation than most commercial products and are designed specifically to work with OCFs.THHN wire is available at your local hardware or electrical supply store and FlexWeave™ wire is available on-line from DavisRF.com or AmateurRadioSupplies.com.