QTH Locator — locations, distance and terrain profile

The module answers two questions: where exactly is that? — and, on VHF/UHF, the more important one: can I get there, or is there a mountain in the way?

Since 1.38 it replaces the earlier QTH locator from the calculator list and is reached from the sidebar.

Setting locations

Two stations: your own QTH and the remote station. Both can be

• placed by clicking the map (⌥-click always sets the QTH),
• dragged with the mouse,
• or typed into the input field. The field accepts a locator (2 to 10 characters), coordinates in all common notations (decimal degrees, degrees/minutes, degrees/minutes/seconds), a map link (Apple, Google, OpenStreetMap, geo:) or simply a place name — the app works out which is which.

Your own QTH comes from Settings → Station; the home function jumps back to it.

What is calculated

Distance, bearing and reverse bearing, QRB points, plus the locator cell as a rectangle on the map — so you can see how large a 6-character square really is compared to an 8-character one. The geodesy runs on the ellipsoid (Vincenty), not on a sphere.

Terrain profile — the actual purpose

Below the map sits the terrain profile between both stations, with:

• line of sight and earth curvature (refraction factor selectable: 4/3, 1, 2, or flat earth for comparison),
• the first Fresnel zone as a band, plus the 60 % limit,
• a plain-language verdict: clear line of sight, Fresnel zone clipped, or obstruction at kilometre X,
• seven key figures: distance, bearing, tightest point, clearance there, Fresnel radius, earth curvature, highest point.

Choosing the band (10 m to 3 cm) visibly changes the result — the Fresnel zone narrows with frequency, and a path that just clears on 70 cm can be blocked on 2 m.

An optional vegetation allowance can be added: elevation models give bare ground, but on a VHF path the forest often decides.

The profile is also available in a separate window (menu Window → Maps, ⇧⌘E) — handy on a second monitor while the map stays in the main window.

Map

Three styles (standard, hybrid, satellite) and optional OpenTopoMap contour lines as an overlay. Tiles are cached locally; areas loaded once stay visible without a connection.

Fair use

OpenTopoMap is a volunteer-run service. The app loads only the currently visible section, throttles requests and keeps tiles — every cached tile is one request less. That is why the overlay is off by default.

POTA and SOTA nearby

Under Nearby you can show parks and summits around your own QTH — radius from 5 to 200 km. Hits appear as pins on the map and as a list with distance and altitude.

Clicking a hit sets it as the remote station — the terrain profile to it appears immediately. Exactly the way to check, before an activation, which summit is reachable from home at all.

The search runs offline against the reference databases that HAM-Tools maintains anyway (Settings → Data). If they are not loaded yet, the list stays empty.

Elevation data

Terrain data comes from swisstopo (default, very precise in Switzerland), Open-Meteo or OpenTopoData (worldwide), depending on the setting. It is cached: a path calculated once opens again without a connection — important in the field.

Locator entry, distance and bearing work without a network anyway; only place search and new elevation data need a connection.

Settings

Under Settings → QTH Locator: units (km/mi, m/ft), locator precision, defaults for new stations (antenna height, band), calculation parameters (sample points, refraction factor, vegetation allowance) and the elevation data source including cache management.

Also a standalone app

The QTH locator is also available as a separate, small macOS app — for anyone who only needs this one tool. Both share the same calculation core.