Terminated Mini Loop Antenna : Small Space Ham Radio Antenna

Are you tired of large antennas that dominate your backyard or balcony? The terminated mini loop antenna offers an elegant solution for ham radio operators with limited space. This relatively simple antenna provides wide multiband access from 160 to 6 meters without requiring a tuner.

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What Makes the Terminated Mini Loop Special?

The terminated mini loop antenna combines elements of loop and terminated designs to achieve directional reception with reduced noise pickup. Unlike large loop antennas that require significant space, mini loops are designed for constrained environments while maintaining directional characteristics through resistive termination.

These versatile antennas typically range from 30 inches to 30 feet in diameter. They can be shaped as squares, diamonds, or triangles depending on your space requirements. The compact size makes them ideal for urban settings, balconies, or rooftops where traditional antennas won’t fit.

terminated mini loop antenna

Essential Components for Your Terminated mini loop antenna

Building a terminated mini loop antenna requires four key components:

Loop Conductor

The antenna conductor is usually made of copper wire (such as #14 AWG) or aluminum tubing. Copper wire offers excellent conductivity and is easy to work with. Aluminum tubing provides better mechanical strength for larger installations.

Terminating Resistor

A non-inductive resistor (typically 390–560Ω) is placed at one end to create the directional radiation pattern. This resistor is crucial for the antenna’s broadband characteristics and directional properties. The resistor must handle your transmitter’s power output.

Balun or Transformer

A 9:1 or 4:1 impedance-matching transformer interfaces with your coaxial feedlines. This component matches the antenna’s impedance to your 50-ohm transceiver. The transformer choice depends on your specific design requirements.

Support Structure

Various support options include fiberglass rods, PVC frames, or simple hanging arrangements. The popular K9AY loop design uses a suspended arrangement from a mast. Choose the support method that works best for your installation space.

VE9OR Design Specifications

VE9OR Physical Dimensions:

Loop diameter: 3 to 4 feet
Wire spacing: Turns every 2 to 6 inches
Conductor: 16 gauge copper wire
Support: 1 inch OD plastic tubing

Electrical Components:

Terminating resistor: 500 ohms, 20+ watts (no capacitor needed)
Impedance matching: 9:1 balun
Input impedance: 450 ohms
Power handling: 5 to 60+ watts typical

Construction Details – Terminated mini loop antenna

Loop Structure

The antenna uses 16 gauge copper wire wound around 1 inch plastic tubing. The circular loop maintains a 3 to 4 foot diameter. Space the wire turns every 2 to 6 inches for optimal performance.

Termination Network

The 500-ohm terminating resistor is crucial for proper operation. This resistor must handle at least 20 watts of power. Unlike some designs, this version requires no capacitor in the termination network.

You can install the terminating resistor at two positions:

At the top of the loop (as shown)
At the 2/3 point around the loop circumference

Feed System in Terminated mini loop antenna

The antenna feeds through a 9:1 impedance transformer. This balun matches the 450-ohm loop impedance to your 50-ohm coaxial feedline. The transformer handles the typical input range of 5 to 60+ watts.

Size Range Flexibility

Terminated mini loop antennas offer remarkable size flexibility, ranging from 30 inches to 30 feet in diameter. This wide range allows you to choose a size that fits your available space while optimizing performance for your preferred frequencies.

Shape Variations

You can construct these antennas in multiple shapes:

Square loops: Easy to build with straight supports
Diamond shapes: Good for vertical mounting configurations
Triangle designs: Useful for limited horizontal space
Circular loops: Traditional shape for balanced performance

Support Structure Options

Choose from various support methods based on your installation:

Fiberglass rods: Lightweight and RF-transparent
PVC frames: Inexpensive and easy to work with
Hanging arrangements: Like the K9AY loop suspended from a mast
Rigid mounting: For permanent installations

Building a terminated mini loop requires basic construction skills. The mechanical assembly is straightforward. The electrical components are readily available from antenna suppliers. Start with quality materials. The 16 gauge wire and 1 inch tubing provide good mechanical strength. Choose a terminating resistor rated for your power levels.

This antenna design ‘Terminated mini loop antenna’ is appeared in facebook group Magnetic loop antennas.

Some interesting comments and feedback of above design are given below.

Marcin Mirek ”That’s not magnetic. You have created inefficient, travelling wave antenna. Electric field dominates, because you have stepped up resistance. Most of power is dissipated in that 500 ohm resistor. Very little is actually radiated”

Sean Lavin ”I’d call it a loaded terminated folded dipole in the shape of a loop”

Phil Beesley “You have made a ‘Terminated Folded Dipole’ I use 2 of them at different angles and they work very well both of them cover the whole of the HF bands and beyond, but the most important thing for me is that they are very good at reducing the amount of noise on any received signal. They are not as good on transmit as a full sized Dipole but they are far better than a Dipole on receive.”

Chuck McAllen “We can all agree that the magnet field is 90 degrees to the electric field on any antenna. The mag loops are probably more directional than this type of antenna. Sure it looks like a dummy load but so do most traveling wave antennas. True efficiency can be determined by experimentation. Mag loops can be inefficient too if a cheap capacitor or weak coupling between the main and drive loop. If this design bothers you, then good, we all get complacent sometimes.”

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