TermiLoop — A Smarter Alternative to the Classic BBTD

One of the most common questions we receive is how to achieve efficient NVIS coverage on 160 and 80 meters in small gardens. The typical recommendation — the Broadband Terminated Dipole (BBTD) or TTFD — may seem convenient, but it's far from optimal when efficiency matters. That’s where our TermiLoop comes in: a compact, broadband antenna that offers significantly improved performance while retaining the all-band convenience.

A Smarter Compromise for Small Spaces, Only 12 Meters Wide!

Covers 160 through 10 meters with < 3:1 SWR when installed flat-top at 6 meters height.

The TermiLoop uses 23 meters of wire in a folded configuration, fed via a 4:1 UNUN at one end, and terminated with a 500-ohm resistor placed just 15-20 cm before the cold side. Unlike a classic BBTD, where the resistor sits at the current minimum (center), this off-center termination preserves much more radiating current along the wire — especially on lower bands. The result? Far less power is wasted in the resistor, making this design inherently more efficient and QRO capable.

Where the Folded Wire Makes the Difference

On higher bands between 40 and 10 meters, this antenna behaves much like an EFOC17 — a 17-meter off-center-fed wire — with similar radiation characteristics. Including DX! But below 17 meters, the folded 29 meters of total wire length comes into play:

  • On 30, 40, 60, 80, and 160 meters, the antenna exhibits a broad and efficient current distribution.
  • The radiation pattern remains suitable for NVIS, while still providing some useful DX performance. Pure NVIS on 60, 80, and 160 meters.
  • Unlike typical BBTDs, which suffer from extreme losses below 10 MHz, this configuration retains usable efficiency thanks to the smarter resistor placement.

DX Performance on 30 and 40 Meters

Unlike traditional BBTDs, which waste most of their low-band power in a centrally placed resistor, the TermiLoop has a far more favorable current distribution. This results in:

  • Less resistive loss, especially on 40 m and 30 m
  • A lower-angle radiation component that supports DX paths — even when installed at modest heights (5–7 meters)
  • A hybrid pattern that provides both NVIS and shallow-angle takeoff, making it ideal for regional and intercontinental contacts

At typical domestic install heights, you can expect:

  • Strong signals into 500–2000 km range (NVIS + short skip)
  • Usable DX capability into 3000–8000 km range with proper band conditions

Higher Bands: 20 to 10 Meters

On the upper HF bands, the antenna acts like a short off-center-fed dipole with a gentle taper in current caused by the termination resistor. While it won't rival a full-size Yagi or elevated monoband dipole in gain:

  • The radiation pattern is stable and largely omnidirectional in azimuth
  • It provides good coverage without nulls, especially useful in unpredictable band openings
  • The termination helps suppress standing wave resonances, which reduces SWR variation across each band
  • Efficiency is comparable to a well-fed EFOC17 — especially on 20 m and 17 m

This makes it well-suited for casual DX operation on upper bands without the need for tuners or band switches.

Quieter Receive Performance

One often-overlooked benefit of the TermiLoop is its quieter receive behavior compared to a standard EFOC antenna. Because the termination resistor damps standing wave resonances and reflections, the antenna exhibits a more uniform impedance profile over a wide frequency range. This reduces the antenna’s tendency to pick up local common-mode noise — especially powerline hash and broadband RF garbage — that often plague resonant or high-impedance antennas.

Furthermore, the folded geometry and balanced structure help ensure symmetrical current flow, minimizing asymmetries that can introduce unwanted common-mode pickup. As a result, the antenna delivers not only smoother SWR across bands but also a noticeably lower noise floor — especially on 160, 80, 60, and 40 meters where man-made noise dominates.

Efficiency and Power Handling

We offer two versions:

  • TermiLoop: Standard version, rated for up to 100 W FT8 250W SSB
  • TermiLoopQRO: High-power version, rated for up to 600 W FT8 and 1500 W SSB

The antenna is built for robustness and long-term durability:

  • SSB: up to 1500 W PEP (QRO version)
  • CW/FT8: up to 600 W PEP (QRO version)
  • CW/FT8: up to 100 W PEP (Standard version)

The folded geometry also doubles the conductor cross-section, reducing loss resistance and increasing current handling.

Summary: A Better BBTD for Real-World Use

If you’re constrained by garden size but need reliable, multi-band performance — especially for 160 and 80 meters NVIS — the TermiLoop offers a compelling solution. You get the broad coverage of a BBTD without the heavy efficiency penalties, and an antenna that behaves like an EFOC17 on higher bands, yet radiates more effectively on 160, 40, and 80 meters.

Whether you're operating portable, setting up a stealthy base antenna, or building a low-profile contest setup, this antenna delivers a smarter compromise — where efficiency meets versatility.

Whether you're operating portable, setting up a stealthy base antenna, or building a low-profile contest setup, this antenna delivers a smarter compromise — where efficiency meets versatility.

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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.