80-meter operation has always been a challenge for amateurs with limited space. A quarter-wave vertical simply isn’t practical for many amateurs, especially those in suburban or urban areas. The antenna shown above provides a practical solution: a compact 4-meter vertical antenna for the 80-meter band using a thoughtful loading and matching strategy.
Physical Layout and Construction
The antenna consists of a 4-meter vertical radiator constructed from 20mm diameter tubing. To increase the electrical length of the radiator, a loading coil of 64.15 microhenries is added towards the bottom of the vertical radiator. This is done to ensure a reasonable current flow while keeping the overall height practical.
The bottom of the antenna is grounded near the ground level, with a clear separation for the feeder connection point. As with all shortened verticals, the antenna’s performance is highly sensitive to the ground system. Even a simple radial system or ground screen will prove to be a huge success in improving efficiency and minimizing ground losses.
Electrical Performance
At the design frequency of 3.650 MHz, the antenna presents a feedpoint impedance of roughly 20.7 ohms. This is not surprising for a shortened vertical and requires a careful impedance matching for efficient power transfer.
For this purpose, a simple L-network matching circuit is used at the bottom of the antenna. The following diagram shows two possible matching circuit designs, depending on the type of coaxial cable used:
50-ohm coax:
Capacitance of 1037 pF and an inductance of 1.07 microhenries
75-ohm coax:
Capacitance of 941 pF and an inductance of 1.46 microhenries
This matching network is used to transform the low feedpoint resistance to a more suitable value for common transmission lines, thus ensuring a low SWR.
Why This Design Works
Short vertical antenna on 80 meters are often criticized, but this is mainly because of improper grounding or improper matching. This design corrects both issues. The large loading coil ensures low resistive losses, and the base matching network enables the user to select the type of coaxage available.
The final result is an antenna that, although small, is very useful for regional and even DX communications when conditions are favorable. It’s especially useful for those who want 80-meter communications without towers, long dipoles, or extensive property.
This 4-meter vertical antenna is a fine example of good antenna design. It doesn’t overpromise, but it does provide a practical, real-world solution for 80-meter communications on a small lot. With proper attention to construction, quality materials, and proper grounding, it should prove a valuable and useful addition to any HF station.
For those who have limited space but no interest in forgoing 80-meter communications, antennas such as this one show that good compromises are still possible and will get you on the air.
Design Credit
The compact 4-meter vertical antenna design illustrated and discussed in this article is credited to UROGT, who developed and published this configuration as an optimized shortened vertical for the 80-meter band. The loading coil values, physical dimensions, and base matching approach shown are based on UROGT’s original work, which has been widely shared and referenced within the amateur radio community for its practical and effective design.
This article presents the antenna for informational and experimental purposes, with full acknowledgment of UROGT’s original contribution.
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