The Loaded Loop Antenna is a clever HF antenna design ideal for radio amateurs with limited space—particularly those operating from apartments or small homes. Originally installed along the perimeter of a brick-house balcony, this antenna demonstrates how thoughtful engineering and creative loading can produce surprisingly effective multiband HF performance. The circuit diagram below shows the construction of a multiband loop antenna that uses an external load and a ferrite core transformer for impedance matching
Antenna Overview
The antenna forms a large loop around the balcony perimeter. It uses 1-mm copper wire and incorporates both a ferrite transformer and a 300-ohm load to improve bandwidth and ensure stable SWR across multiple HF bands.
Key Dimensions
- Height: 1.2 m
- Bottom width: 2.5 m
- Side sections: 1.0 m each
- Symmetrical loop layout
This makes it an excellent choice for installations where a full-sized HF antenna is not practical.
Transformer Construction
A unique feature of this design is the transformer wound on six ferrite rings with:
- Permeability: 30
- Outer Diameter: 30 mm
- Inner Diameter: 20 mm
- Height: 8 mm (each)
The transformer uses 12 turns of triple-stranded 1-mm wire. This winding scheme improves coupling and helps achieve wideband matching to the feedline.
Feedline: 75-ohm coaxial cable
Load: 300-ohm termination (built from 18 × 150-ohm / 2-W resistors)
A 300-ohm loading resistor is placed at the bottom-center of the horizontal section. It is built using 18 resistors, each rated at 150 Ω / 2 W. The antenna has been tested with a maximum power of 50 W.
When compared to a vertical antenna installed on the roof, the loaded loop was found to have a lower efficiency, with the vertical having a gain of “at least 3 ball on scale RS”. Despite this, the antenna’s ability to facilitate international contacts on higher bands suggests it’s a valuable asset for limited-space operations.
This Loaded Loop Antenna design was created by Vaclav and featured in ANTENTOP-01-2019, # 023. You can watch a video about a similar build here: Full Build Deploy & Test – Multiband 40m Shortwave Radio Delta Loop.
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