- Like many fellow radio amateurs, I own a fairly standard shortwave radio station consisting of a 100W HF transceiver driving a 1kW tube power amplifier. I never chose to spend any money on a kW-rated antenna-tuner. Anyhow, I can tune out VSWRs as high as 3÷1 with the adjustable pi-network of the output filter tank inside my power amplifier.
Thus I set out to design an HF antenna with a VSWR of 3÷1, or less, over the full bandwidth of as many amateur radio HF bands as possible. At the same time, my preference went out to the low- and the non-WARC bands. This design exercise resulted in a new kind of antenna which I dubbed Center-Loaded Off-Center-Fed Dipole Antenna, or CL-OCFD for short.
- In proof of its performance, an EZNEC-calculated VSWR-graph of the CL-OCFD antenna is presented in Figure 2. This antenna works without a tuner over the entire bandwidth of the 80, 40, 30, 20, 15 and 10m-band, simply by adjusting the output-tank of your tube power amplifier. —If your final output stage is a transistor amplifier, you definitely will need an antenna-tuner though.— In such, this antenna is the first described single-wire antenna to be offering these capabilities.
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