Propagation and solar conditions¶

Knowing whether a band is open beats calling into static. Two kinds of tool answer that: software this catalog installs, and websites that are better than anything installable. The websites live here as prose — AHRL shipped them as browser bookmarks and menu launchers, and this project retired those units (a menu entry that opens a URL is not software, and it rots exactly as fast), keeping the destinations where documentation belongs instead.

Installed tools¶

hamclock-next — the kitchen-sink dashboard: space weather, band conditions, DX spots, satellite passes, all on one screen.
splat — RF path modeling over real terrain, for point-to-point questions rather than ionospheric ones.
signal-server — coverage maps over the same terrain, every input on the command line; see Terrain for coverage plots below.
WSJT-X's own WSPR mode — the empirical answer: beacon a few milliwatts and see where you are actually heard.

Terrain for coverage plots¶

Above about 30 MHz the question is what is in the way, and SPLAT! and Signal-Server answer it from elevation data. Without that data both still run: they assume a flat earth at sea level and print a confident answer that is worthless. So the first job is terrain.

Where the terrain comes from¶

splat-sdf (in the antenna profile) makes SPLAT's terrain files from the elevation Hammunition already holds for your map regions: the Copernicus 30 m tiles (dem-copernicus), or USGS 3DEP when you chose it with hammunition station set --dem-source 3dep. It writes two files per one degree square, compressed, under /usr/local/share/hammunition/data/splat-sdf/:

File	For	Resolution
`36:37:116:117-hd.sdf.bz2`	`splat-hd`, `signalserverHD`	one arc second, about 30 m
`36:37:116:117.sdf.bz2`	`splat`, `signalserver`	three arc seconds, about 90 m

and beside each a link under the name Signal-Server asks for (36_37_116_117-hd.sdf.bz2). The square in the names is south-west corner 36 N 117 W, counted west and positive the way SPLAT! counts longitude.

With no map regions set, splat-sdf is deferred by name and nothing is made; set them first:

hammunition station set --map-regions <region>
hammunition install antenna

The plan lists the tiles to download, the files to make and the disk they take before anything happens. One tile took about 15 s and 151 MB of memory to convert, and its two files are 6.5 MB (measured on one Copernicus tile; a whole region has not yet been run through an install).

What the converter does differently from SPLAT's own instructions. SPLAT's srtm2sdf tools replace every elevation below zero with their neighbours' average unless told otherwise, which turns Death Valley, the Dead Sea or a polder into dry land. Hammunition runs them with -n -32767, so only true gaps in the data are filled.

Point SPLAT! at it¶

Run this once, as yourself:

hammunition maps splat

It writes ~/.splat_path, the file SPLAT! reads for its terrain directory, when you have none. If you already have one naming another directory it is left alone, and the command tells you to pass -d instead:

splat-hd -t site.qth -r other.qth -d /usr/local/share/hammunition/data/splat-sdf/

A coverage plot from `FN31pr`'s centre¶

FN31pr is the documentation's placeholder grid square; its centre is 41.7292 N, 72.7083 W. Put your own position in its place, and make sure your map regions cover the area the plot reaches, or the squares without terrain read as sea level.

Signal-Server, a 2 m station 10 m up at 50 W ERP, 30 km out:

signalserverHD -sdf /usr/local/share/hammunition/data/splat-sdf/ \
  -lat 41.7292 -lon -72.7083 -txh 10 -f 146.52 -erp 50 -rxh 2 -m \
  -R 30 -res 3600 -pm 1 -rt -100 -dbm -nothreads -o fn31pr-coverage

It writes fn31pr-coverage.ppm, the map, and fn31pr-coverage.dcf, the colour key in dBm. Any image viewer that reads PPM opens it; ImageMagick's convert fn31pr-coverage.ppm fn31pr-coverage.png makes a PNG. -pm picks the propagation model (1 is ITM, Longley-Rice; its usage text lists all twelve). signalserver, without HD and without -res, reads the 90 m files and is much faster.

Always pass -nothreads. Measured on 2026-10-01 over one tile at a 20 km radius, the threaded 30 m plot crashed 2 times in 10 and the unthreaded one completed every time it was run, in 19 to 29 s with 1.36 GB of memory; the 90 m plot took 1 to 2 s and 600 MB. A missing terrain file is not an error in Signal-Server either: the square is taken as sea level with a warning in its log, and it exits 0.

SPLAT!, line-of-sight coverage from the same spot, with a 2 m receiving antenna. A site file gives the name, latitude, longitude west and positive, and height:

printf 'FN31pr\n41.7292\n72.7083\n10 meters\n' > fn31pr.qth
splat -t fn31pr.qth -c 2 -R 30 -metric -o fn31pr.ppm -geo

splat covers up to 8 square degrees and splat-hd 4, by their own build; on one tile a 20 km coverage map took splat 1.3 s and splat-hd 22 s. -geo writes a .geo file beside the map, which is how Xastir lays a picture over its own maps: the plot becomes an Xastir layer.

Which readers the terrain serves¶

Program	Reads	Served
QMapShack	one virtual raster over the tiles	yes, `dem-qmapshack`
SPLAT!	SPLAT Data Files	yes, `splat-sdf`
Signal-Server	the same files under its own names	yes, `splat-sdf`
Xastir	a GeoTIFF or a `.geo`-described image	not yet: an elevation layer for Xastir would be a shaded-relief image per tile with a `.geo` file beside it, not built because nobody has measured Xastir drawing one; SPLAT's `-geo` output is a layer today
gpredict, hamclock-next	nothing	a horizon mask from the elevation is what a satellite station would want; after 1.0

What has not been measured yet¶

splat-sdf through hammunition install on a real region: its time, memory and scratch over tens of tiles;
SPLAT! and Signal-Server plots over that region on the field laptop;
Signal-Server's threaded crash on other hardware, and the square east of Greenwich, whose name Signal-Server builds differently from SPLAT! (read from its source, linked accordingly, not run).

The sites worth knowing¶

PSKReporter — who is hearing whom, right now, on which band, from real decodes. The single most useful propagation page in amateur radio: before you call, see whether anyone on the far end is decoding your band at all.
VOACAP Online — point-to-point HF prediction: your station, their station, and the probability a circuit exists at each hour and frequency.
N0NBH solar data — Paul Herrman's solar-terrestrial banners: SFI, A and K indices, band-by-band condition calls at a glance. (AHRL's solar_data unit fetched one of these banners with wget and displayed it with a deprecated ImageMagick command — this link is that unit, without the plumbing.)
DXLook — live DX activity on a map, cluster spots and FT8 decodes merged.
HamTab — a shack browser-tab dashboard: clocks, conditions, spots in one page.
Open HamClock — the web face of the HamClock world; the installed hamclock-next is its desk-side sibling.

RF exposure¶

AHRL's rf_exposure_calc unit was a two-line script opening hintlink's power-density calculator in a browser. For US operators the durable reference is the ARRL's RF-exposure material and the FCC's own calculator requirements that took effect in 2023 — run your numbers when you change antenna, power, or shack layout, not once ever. The hamexposure.org calculator implements the FCC formulas directly.