As an Amateur Radio Enthusiast, I take great pride in designing and building my own antennas. This OCR HF Dipole Antenna is 69 ft. end-to-end in length and designed to work on the 40-20-15-10 amateur bands. When fed from 50-ohm feedline coax, a 4:1 Quanella Current Balun makes it a true balanced antenna. It is rated to handle 1.5KW Tx power although I’m only capable of transmitting 100W maximum. This was a very gratifying project, and I learned a lot.
Design and Simulation
Given the constraints of my backyard, the antenna’s highest point is only 20ft. so most of the gain is straight up into space. The off-center feed ratio is 2:1 i.e. 46:23 ft.
Construction
Except for the two size 240 ferrite toroids (type 61), all other components were sourced from my local home improvement center for a total cost of about $100. The wire elements are insulated copper, #14 gauge. Other components are made from Stainless Steel.
Testing and Tuning
The VSWR empirical plot above indicates the OCF antenna is below 2:1 on 40, 20, 15, 10-meter radio bands i.e. (7, 14, 20, 28 MHz). Using external Antenna Tuner equipment is unnecessary. The measured VSWR plot is much more optimistic than the EZNEC simulation.
Tuning was performed by clipping small lengths of wire from both ends of the dipole antenna elements in a 2:1 ratio according the OCF ratio, up to 21 total inches, then measuring SWR after each iteration. At some point I decided that SWR was “good enough” across both 40 and 20 meter bands and quit tuning.
Conclusion
Finally, I’m on-the-air from my backyard in North America. Despite the low height compromise, I’ve made more than 200 FT8 QSO contacts in 6 continents. SSB contacts range to about 1,000 miles. My antenna has been up and down several times due to yard maintenance issues (including tree removals) and refurbished and upgraded a few times but remains fully operational for over 6 years (since 2018).