LoG with a 9:1 Transformer? Why It’s Quiet — But Not Efficient

Rethinking the Loop on Ground (LoG) for NVIS Reception

Why it’s a linear H-field current sensor — not an impedance trick

Misconceptions About the LoG

Most "hamster wisdom" online treats the LoG as a magical low-noise antenna that just needs a 9:1 transformer to work. These implementations often fall into the trap of matching the loop to a receiver’s input impedance via brute-force impedance transformation — ignoring the real physics of what's happening.

But the Loop on Ground is not about impedance — it’s about current.

In fact, the performance of a LoG is governed far more by its physical size, geometry, proximity to ground, and symmetry, than by any matching box you slap on it.

The LoG is a Linear H-Field Sensor

Let’s get this straight:

  • A LoG is an H-field antenna — it responds to time-varying magnetic fields, not electric fields.
  • It’s typically a large (~16 m perimeter) horizontal loop, laid just centimeters above lossy soil, so it's operating in a very non-ideal magnetic field zone.
  • The voltage induced across the loop terminals is proportional to the time derivative of the magnetic flux through the loop: 


    V = -N · dΦ/dt

    where Φ is the magnetic flux.

Since the loop is not resonant, not shielded, and not elevated, it doesn’t behave like a magnetic loop in the traditional sense.
Instead, it acts more like a linear current pickup system, measuring local ground-parallel H-fields from skywave signals (especially those arriving at steep NVIS angles).

Why Passive 9:1 or 6:1 Designs Are Fundamentally Inefficient

Most ham-built LoGs use a 9:1 transformer to try and match the loop to a 450–600 Ω receiver input. While this "works" in the sense that it delivers a usable signal, it comes at a steep cost:

  • You lose signal power across the wideband mismatch.
  • You get poor common-mode rejection, especially if the coax forms part of the loop current path.
  • You invite environmental noise — especially from the coax shield or from nearby buildings.

The transformer sees a wildly varying loop impedance, especially on higher bands, and does little to prevent coax-induced CMCs.

A Wire Near Ground Doesn’t Resonate — No Matter How Long

A wire placed on or very close to ground does not behave like a traditional resonant longwire, even if it's multiple wavelengths long.

Here’s why:

  1. Ground absorbs energy rather than reflecting it.
  2. Image currents in the lossy ground are anti-phase, suppressing standing waves.
  3. Radiation resistance is extremely low, dominated by losses.
  4. Current distribution is linear, not sinusoidal — indicating traveling wave behavior.

That’s why you can’t create an efficient impedance swing near the ground — the system behaves more like a leaky transmission line, not a resonator.

From NVIS to DX: Leveraging Wire Length for Optimized Reception

Once you understand that a near-ground wire behaves as a traveling-wave H-field sensor, you can tune its behavior by length, not impedance.

That’s exactly what we’ve done with the TerraBooster series:

TerraBooster Mini

Compact NVIS design using a short 8–10 m wire, shielded coax, and high-CMRR differential amplifier.
Optimised for 160–40 m, steep NVIS angles, and urban RFI rejection.

TerraBooster Medi

Mid-length (16–20 m) for more forward gain and a slightly lower elevation angle.
Great for 80–30 m with mixed NVIS and short skip.

TerraBooster Maxi

Beverage-like behavior using a 25–30 m wire. Broader angular coverage and excellent F/B.
Ideal for 30° DX reception on 160–20 m.

TerraBooster Xtreme

Longwire version focused on low-angle DX reception from 30–10 m, centered around 10–20° elevation.
Optimized for greyline and long-path.

All models except the Xtreme use shielded coax, a high-impedance CR filter to ground, and differential buffering to reduce E-field noise and enhance CMRR.

Summary: Design for Geometry, Not Impedance

If you build a LoG and just slap a 9:1 on it, you’ll get something. But if you design it as a true H-field current sensor, optimized for ground coupling and current symmetry, you’ll get a high-performance broadband RX system.

Stop chasing resonance. Start designing with physics.

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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.