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

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

Rethinking the Loop-on-Ground for NVIS and low-band HF reception — with physics, not folklore

Misconceptions About the LoG

A lot of online LoG writeups treat it as a magical low-noise antenna where a generic “9:1 box” is the entire secret. In practice, that framing confuses impedance transformation with why the LoG is quiet.

A LoG’s real performance is dominated far more by geometry (loop size and shape), height above ground, soil conductivity, and—crucially—balance/symmetry and feedline isolation than by any “matching trick.”

So: the LoG isn’t a resonance game or an SWR game. It’s largely a current-control and common-mode control game.

The LoG is a Broadband, Ground-Coupled Receive Sensor

Let’s get the core idea straight:

• A Loop on Ground (LoG) is typically a horizontal loop of insulated wire laid on or just above real, lossy soil (often on the order of ~60 ft / ~18 m perimeter, but not critical).
• Because it is so close to ground, it is extremely lossy and therefore receive-only in almost all practical installations.
• In ideal form, the loop’s open-circuit output can be described by Faraday’s law (magnetic flux linkage):

V = -N · dΦ/dt

…but unlike an elevated, tuned “magnetic loop,” a LoG is heavily influenced by ground coupling. Ground proximity damps resonant behavior, changes polarization response, and can suppress pickup from some local near-field noise sources. That’s a big reason LoGs can sound “quiet” even when absolute signal voltage is modest.

Important nuance: at ground level, ground reflection strongly alters what field components dominate. A ground-mounted horizontal wire structure tends to respond primarily to the vertically polarized component of skywave once the ground-reflected wave is considered, and the elevation response can be relatively broad—useful for both regional/high-angle (NVIS-like) and low-angle (DX) reception, depending on band and site.

Why “Just Use a 9:1” Is an Incomplete Answer

Most LoG builds use a transformer ratio in the “several-hundred-ohms to 50–75 Ω” range because the loop’s feedpoint impedance is typically a few hundred ohms over its intended HF range. That’s why ratios around 9:1 (to 50 Ω) or ~6:1 (to 75 Ω) are common.

But the transformer is not there to chase a perfect wideband match. In a well-behaved LoG system it mainly exists to:

• Provide galvanic isolation so the loop can float and the feedline doesn’t become part of the antenna.
• Provide a practical impedance step-down so coax loss stays low and the receiver (or buffer) sees a sensible source impedance.
• Preserve balance so the loop’s current distribution stays symmetric and environmental E-field pickup stays minimized.

Where many “quick build” LoGs fall down is not the turns ratio—it’s common-mode current:

• If the transformer is a non-isolated autotransformer, or if the loop/feed is not symmetric, the coax shield can become the real antenna.
• Without strong common-mode choking (ideally at the feedpoint and again at the receiver end), household RFI can ride in on the feedline and erase the LoG’s noise advantage.

And a reality check: the LoG is intentionally low-gain. If your LoG does not set the receiver noise floor on the bands you care about, then adding a low-noise buffer/LNA at or near the feedpoint can be beneficial—provided you do it without sacrificing balance and isolation.

A Wire Near Ground Isn’t a High-Q Resonator

A conductor placed on (or a few centimeters above) real ground can still show impedance variations and resonant features, but they are usually heavily damped and far less “tunable” than an elevated wire.

Why the resonance-chasing mindset breaks down near ground:

1. Ground losses dissipate energy and reduce Q (broad, weak impedance features).
2. The “image” in lossy ground is attenuated and phase-shifted, changing current distribution and smearing standing-wave behavior.
3. Radiation resistance collapses as height approaches zero, so loss dominates.

So instead of trying to “tune” a LoG like a longwire, treat it as a broadband, ground-coupled receive sensor: optimize geometry, keep it symmetric, and control common-mode currents aggressively.

From NVIS to DX: Leveraging Geometry and Length Intentionally

Once you view near-ground receive structures as broadband sensors, you can influence what you hear by changing aperture (area/length), orientation, and feed symmetry—not by chasing a narrow resonance.

This is the thinking behind the TerraBooster series: applying LoG-style ground coupling plus high-CMRR buffering to different near-ground geometries.

TerraBooster Mini

Compact, high-rejection receive sensor using a short 8–10 m element, shielded coax, and a high-CMRR differential amplifier.
Designed for 160–40 m where urban RFI rejection and regional/high-angle reception are often more valuable than raw signal voltage.

TerraBooster Medi

Mid-length (16–20 m) to increase aperture and sensitivity, with a stronger tendency toward lower elevation angles as frequency increases.
A practical choice for 80–30 m when you want one system to cover regional and medium-haul paths.

TerraBooster Maxi

Longer element (25–30 m) that can develop a clearer forward preference on higher HF bands, while remaining broadband and ground-coupled.
On the lowest bands it is still electrically short, so directivity and F/B are site dependent (soil, surroundings, layout), but it can be very effective as a “quiet” wideband RX element from 160–20 m.

TerraBooster Xtreme

Long-wire variant aimed at 30–10 m where the element is a meaningful fraction of a wavelength and low-angle DX paths can be emphasized.
Actual takeoff angles and directivity remain site dependent (soil, length, termination strategy, and nearby structures).

All models except the Xtreme use shielded coax, a high-impedance RC reference to ground, and differential buffering to reduce E-field ingress and maximize common-mode rejection.

Summary: Design for Geometry and Isolation, Not “Magic Matching”

A LoG with a generic 9:1 transformer can absolutely work — and it can be wonderfully quiet. But the quietness comes from ground coupling, loss, balance, and isolation, not from pretending the loop is a wideband, perfectly matched resonant antenna.

Stop chasing resonance. Start designing with physics: geometry, symmetry, and common-mode control.

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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.