Anyone who has ever operated a station in an urban or suburban environment knows the problem: the noise floor on the 80 and 160 m bands is so high that weak stations simply fade into the background. There are several causes — switching power supplies from computers, LED lighting, chargers, solar inverters, neighboring devices. All these sources of interference spread into the environment, and your transmitting antenna picks them up just as readily as useful signals.
Riešením nie je väčšia antenna ani vyšší výkon. Riešením je dedikovaná príjmová antenna navrhnutá tak, aby preferenčne zachytávala vzdialené, nízko-uhhlové signály a potláčala lokálne rušenie šíriace sa vertikálnou zložkou poľa. Loop On Ground — skrátene LOG — patrí práve do tejto kategórie. Anténa je zo svojej podstaty pasívna, nevyžaduje napájanie, nevyžaduje montáž vo výške a spolupracuje so zemou ako súčasťou svojej geometrie. Práve vďaka tejto geometrii vykazuje výrazne nižší príjem lokálneho rušenia v porovnaní s bežnou vertikálnou alebo dipólovou anténou používanou na príjem.
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Does Loop On Ground work?
The original design comes from Chris Mosher, KK5JY, and is detailed on his website. The principle is that a wire loop placed directly on the ground — or just above it — has a vertical aperture practically equal to zero. It primarily receives the horizontal component of the electric field, not the vertical. Local interference predominantly spreads through the vertical component, while distant HF signals arrive at a low angle and contain sufficient horizontal components. The result is selectivity that is not a result of antenna direction in azimuth, but of the physics of radio wave propagation.
The manufacturer Omni RF Ltd describes its own experiences from product development as follows:
Noise S9+10 dB on the 80 meter band disappeared and was replaced by cleaner signals with an SNR improvement of between 3 and 6 dB.
Ide o pasívnu anténu bez aktívnych prvkov, preto zisky oproti vysielacej anténe nie sú jej cieľom — cieľom je zlepšenie pomeru signál/šum na pásmach, kde lokálne rušenie degraduje príjem. V praxi to znamená, že slabé stanice, ktoré pri príjme cez vertikálnu anténu zanikajú v šume, sú na LOG čitateľné.
A loop installed as a square with power in the corner exhibits some directivity in the horizontal plane at low elevation angles. The exact directional pattern depends on the symmetry of the installation, soil characteristics, frequency, and surrounding structures. The best results are achieved by experimentally rotating the square and comparing SNR on target signals.
What is the Omni RF Loop On Ground antenna made of?
Omni RF Ltd z Veľkej Británie vyrába systém LOG ako dvojdielnu sadu, pričom transformer a wire element are available separately or together as a kit. Each component is handmade in its own workshop.
Transformer
The transformer core is wound on original Fair-Rite cores with enameled copper wire with its own turns ratio, which was the result of six months of measurement and optimization. Compared to the original KK5JY design, Omni RF uses a different type of core, which the manufacturer claims provides lower losses and better performance at lower bands. The transformer is available in three versions according to output impedance and connector:
| Version | Impedance | Connector |
|---|---|---|
| SO239 | 50 Ω | SO239 UHF |
| BNC | 50 Ω | BNC |
| F Type | 75 Ω | F connector |
The enclosure is printed from ASA material - a type of ABS with better UV resistance - with a tinned PCB treated with a solderable conformal coating for moisture protection. All screws and nuts are made of stainless steel A2. The package includes a galvanized steel stake for anchoring in soft soil.
The PCB includes jumpers for future expansions - planned additional modules include an active preamplifier, a band-stop filter for AM broadcast, and an experimental board. These modules are not yet for sale at the time of writing this article.
Wire element 'Omni Flex'
The element is made from a custom specification of wire 'Omni Flex': 22 strands of pure copper with a total conductor diameter of 0.75 mm, insulation made of black halogen-free polyolefin. The material is very flexible with virtually zero shape memory and operates in a temperature range of -25 to +90 °C. The element is available in two lengths:
| Variant | Total length | Square side | Suitability |
|---|---|---|---|
| 60′ | 18.3 m | 4.6 m | 30 m and higher bands |
| 100′ | 30.5 m | 7.6 m | 160, 80, 60, 40 m |
The wire is marked at intervals with heat shrink tubing and finished with crimped M6 connectors with heat shrink protection for connection to the transformer. The package includes four galvanized steel stakes for anchoring corners in soft soil.
Distributors
Omni RF Ltd sells products exclusively through authorized distributors. Currently, the following options are available:
| Distributor | Region | Web |
|---|---|---|
| ML&S Martin Lynch & Sons Ltd | United Kingdom (exclusive retail sales) | hamradio.co.uk |
| PileupDX.com (pileup Communications AB) | Europe | pileupdx.com |
PileupDX offers a complete kit (SO239 transformer + element) in two sizes — 18.3 m and 30.5 m. Prices are listed in USD, EUR, and SEK according to the current exchange rate on the seller's website. The transformer and element are also available individually directly on the manufacturer's site omni-rf.com, where there is also a current list of distributors.
Summary
beverage antennasand for experimenters who want to have a solid reference point for further comparisons.
The antenna is not a substitute for a transmitting antenna and is not intended for transmission — it is a tool to improve reception in conditions where the transmitting antenna is not sufficient as a receiving antenna.