Project - Researching, Designing and Building a UHF Horizontal Wire Loop Aerial (UHFHWLA)

The UHF Horizontal Wire Loop Aerial (UHFHWLA) is a simple yet effective DIY antenna project designed for UHF frequencies, particularly for monitoring UHF CB and other active users in the band. This aerial builds on principles learned from ultralight DXing tools like Ferrite Sleeve Loop (FSL) antennas. While FSLs excel in MW and LW bands, this UHF counterpart harnesses the benefits of compact design, easy tuning, and strong performance at higher frequencies.

This post covers the design, testing, construction, and results of the Mark 1 UHFHWLA, focusing on its performance with UHF TASGRN control channels.

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Background and Motivation

As an avid DXer, I’ve worked extensively with Ferrite Sleeve Loop (FSL) antennas for ultralight radio DXing. These antennas have shown me how small, efficient designs can transform reception capabilities. Moving into VHF and UHF frequencies, the principles of compact loops scale beautifully. Since higher frequencies have shorter wavelengths, this project became an accessible experiment with a practical application: improving UHF CB and 420MHz trunked system reception.

The target: UHF TASGRN control channels (420MHz) and general UHF CB monitoring.

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Design Concept

The UHFHWLA employs a simple horizontal loop design, making it:

• Easier to construct than vertical dipoles or Yagis.
• Compact and lightweight, leveraging UHF's short wavelength.
• Capable of providing some directionality for signal identification.

To evaluate performance, I decided to test two configurations:

1. One wavelength loop (e.g., 70cm length for 440MHz 70CM amateur radio band).
2. Two-wavelength loop, double length (140cm), for potential gain improvements. This longer length should also improve VHF signal reception.

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Materials and Construction

Materials

• Two empty paper rolls (lightweight yet sturdy forms for the loop ends).
• Wire (cut to precise lengths for resonance at UHF frequencies).
• Adhesive tape (to secure the wire and maintain shape).
• Cable ties (planned for Mark 2 for better structural integrity).
• BNC Connector.

Construction Process

1. Measure the wire:

   • For one wavelength: Calculate using the formula
     $\text{Length (m)} = \frac{\text{300}}{\text{Frequency (MHz)}}$.
     Example: For 440 MHz, the wavelength is approximately 70cm.
   • Double the length for the two-wavelength loop. 140cm, this also provides some level of gain.

2. Prepare the forms:

   • Tape the wire around inner paper roll, to maintain a consistent circular shape.

3. Join the wire ends:

   • Secure the loop with adhesive tape to ensure a stable connection. Cut the other paper roll length ways and place this over the inner roll.

4. Attach to the BNC connector:

   • Attached this via wire, for a reliable test. MK2 will see this replaced with cables ties.

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Testing and Results

Testing Parameters

• Frequency focus: UHF TASGRN control channels (420–430MHz range).
• Equipment: Uniden BC95XLT scanner and log sheet.
• Comparison: Benchmarked against the standard whip and a single wave length aerial.

Findings

1. Performance improvement:

   • Logged 30% more TASGRN control channels compared to the whip.
   • Stronger signal reception across multiple sites.

2. Directionality:

   • The loop exhibited a subtle ability to null out off-axis signals, aiding in signal identification and reducing interference.

3. Configuration comparison:

   • The two-wavelength loop showed better gain, especially for distant signals.
   • However, it was less practical for portable use.

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Room for Improvement: Mark 2 Plans

The UHFHWLA Mark 1 demonstrated promise, but there’s room to refine its design for durability and ease of use:

• Structural improvements:

  • Add cable ties for a stronger loop form.
  • Wrap the assembly with protective tape to guard against wear.

• Labelling:
  

  • Mark the loop with its frequency range for easier field identification.

• Connection enhancements:

  • Explore better connectors for cleaner signal transfer.

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Conclusion

The UHF Horizontal Wire Loop Aerial is an excellent starting point for DIY antenna enthusiasts focused on UHF monitoring. Its simple design and measurable performance gains make it a valuable addition to any radio monitors toolkit. Testing with TASGRN control channels proved its utility, logging more signals with stronger reception and some directionality.

Mark 2 improvements are already in the works, aiming to make this aerial even more robust and user-friendly for extended field use. This project highlights how accessible and rewarding antenna experimentation can be, especially at higher frequencies like UHF.

18/11/2024 - UHFHWLA MK2

Following my research, design and build of my UHF Horizontal Wire Loop Aerial (UHFHWLA) MK1, I spent some time today working on some updates and improvements for MK2, these include:
- Sealing the loop with tape.
- Using cable ties to attach this to the BNC connector and improving where this is connected, it is now on the rear and this both makes it stronger and also means the radio won't fall over as easily.

My testing today, when the bands are more active has shown this has a marked improvement on the UHF band. On the VHF band, it is about equal with the standard aerial. The changes can be seen in the photos below.