23-03-2018, 09:40 AM
Many people don't like them, but in my experience, a properly constructed OCF dipole will work extremely well. I never experienced any TVI issues.
I was able to stack 80m and 30m OCF antennas quite successfully, feeding with 300 ohm ladder line to a 6:1 balun. It had the bonus of working on all WARC bands with very low SWR. Stacking will not work with even harmonics.
As an experiment, I then added two 80 metre coaxial traps at the end of the 80 metre OCF and added additional wire for 160 metres. I found that by adding two wires at each end at about 120 degrees, keeping to the OCF 2:1 proportion, I was able to widen the bandwidth. The only drawback was high noise level, but with digital modes like FT8, it was less of a problem.
A high impedance feed lets you get away with a multitude of sins. Make sure you use a balun designed for 160m if you plan to operate on that band.
I can see the attraction of magnetic loops, and I'm thinking of building one as a receive only antenna. On the lower frequencies, they tend to have very low efficiencies on transmit, but they are low noise and able to null out local QRM.
I was able to stack 80m and 30m OCF antennas quite successfully, feeding with 300 ohm ladder line to a 6:1 balun. It had the bonus of working on all WARC bands with very low SWR. Stacking will not work with even harmonics.
As an experiment, I then added two 80 metre coaxial traps at the end of the 80 metre OCF and added additional wire for 160 metres. I found that by adding two wires at each end at about 120 degrees, keeping to the OCF 2:1 proportion, I was able to widen the bandwidth. The only drawback was high noise level, but with digital modes like FT8, it was less of a problem.
A high impedance feed lets you get away with a multitude of sins. Make sure you use a balun designed for 160m if you plan to operate on that band.
I can see the attraction of magnetic loops, and I'm thinking of building one as a receive only antenna. On the lower frequencies, they tend to have very low efficiencies on transmit, but they are low noise and able to null out local QRM.