Site requirements

Where it works

Good sites, in order of preference:

1. A lake or reservoir with open water in front of the antenna across a wide azimuth range.
2. A wide river or a canal seen along its length, or from a bridge.
3. The sea in sheltered places (waves and tides make it harder).

Test installation at a good site: the unit on a lake-side wall facing wide, open water.

Requirements (rules of thumb)

• Open water covering the footprint for the chosen elevations: tens of metres for a 2–5 m antenna height.
• A reasonably flat reflecting surface. For ground sites the literature asks for slopes below about 4% within 50 m; for water the issue is waves and wind.
• An unobstructed view toward the water between about 5° and 45° of elevation: no wall, railing, tree or building in the sector.
• No other strong reflectors in the sector (metal roofs, cars, quays); they produce a second peak in the periodogram.
• A stable mount, and a rough idea of the antenna height (± a few metres) to check the first results.
• 1–10 m above the water is the most comfortable range; more height means a larger, farther footprint (needs more open water) and faster oscillations.
• Draw the sectors on the Station compass toward the water, as wide as the open water allows: wider sectors see more satellite passes. Up to eight separate sectors, each with its own start and end, so they can follow an irregular shoreline and skip what is in the way. The elevation window (any minimum below the maximum, about 5° to 45° recommended) applies to all of them; Station can suggest both from the mapped water.
• The unit sits with its lid toward the water: the sectors must be on the lid side. The solar panel should face the sun.

Seen from above: up to eight sectors, each with its own start and end, drawn toward the water around the unit. Inside them, reflections land on a ring of water: near the unit for high satellites (45°), far for low ones (5°). Not to scale.

Seen from the side: a reflection at elevation e lands H / tan(e) from the antenna, about 11 × H at 5° and 1 × H at 45°. The water between the two must be open.

The Station page draws the same on the map for your site: the sectors, the footprint and the first Fresnel zones, on the mapped water.

Useful satellite passes

A satellite that only crosses the sector is not enough. A measurement comes from a pass that sweeps a range of elevation inside the window while its reflection stays on the water: the C/N0 must go through at least two full oscillations (interference fringes) for the periodogram to give a height, and every extra fringe makes the peak sharper. The unit rejects shorter arcs (fail, geometry).

• Rising and setting satellites are the useful ones: they sweep the low elevations, where the elevation changes the reflection fastest.
• A satellite that stays high, or skims the edge of the sector, changes elevation little while it is over the water: it gives no arc.
• The minimum sweep depends on the antenna height and on the elevation: starting from 5°, about 7° for an antenna 1.5 m above the water and about 4° for 3 m; higher in the sky the same number of fringes needs more degrees.

The Live page shows, for each active arc, how much of the window it has swept; the predicted tracks show which satellites will rise or set through your sectors in the next hours.

Obstructions on the reflected path

The receiver seeing the sky is not enough either: the reflected signal must reach the water and come back to the antenna. A house, a tree, a railing or a boat between the antenna and the reflection zone, or around it, blocks or disturbs the reflected path even when the direct signal arrives clean.

The field console shades in black the part of the footprint hidden by the terrain. That shading is indicative: it comes from a terrain elevation model, which has no buildings or vegetation and does not judge the first 100 m around the antenna. Look at the reflection zones on site, in every sector, and narrow the sectors or the elevation window where something stands in the way.

Signs of a poor site

Visible in the Live page:

• satellites in the sectors that never appear, or appear only with weak (red) signal: the sector is obstructed;
• arcs that close with “fail” for geometry or peak-to-noise reasons;
• periodograms with several peaks of similar size: more than one reflector.

Not sure whether a site works? A Campaign run tells you, without a computer, whether and in which directions it produces usable reflections.