How to play, and the radio behind it

A guide to your first operating day, and the radio ideas behind each opening.

This is a game, and the propagation is simplified on purpose, so please don't plan a real contact with it. For real conditions use VOACAP or a live propagation map.

How to play

Press Play today's round for the same UTC-seeded puzzle as everyone else, or Practice to set your own solar flux and K. Read the conditions, find a station whose listening window is open, set up the rig and press Call. Work each of the ten stations once before the day ends.

Station

Pick a fictional station from the list, the globe pin or the station selector. You'll see its location, locator, rarity, listening window, bands and modes before you transmit.

Band, mode and power

Choose from eleven bands, three modes and 5, 50, 100 or 400 W. Tuning costs no game time. Antenna and band pairs that don't work are greyed out, with a note saying why.

Antenna and bearing

Pick an antenna that suits the distance. The bearing control only appears for the Yagi.

UTC clock

Use +10m, +1h, the slider or Wait for window. Time can't go backwards, and a call that starts at 23:50 ends the day at 24:00.

Calling

A call costs ten minutes even when the station is off air or the path fails. A station you've worked is logged once. When a call fails, the hop table tells you what stopped the signal.

Hints

Show the MUF or the D-layer loss for 5% off that contact's points each, or a rough six-hour MUF scope for 10%. Each hint is charged once, only for that station, and they add up. Stations you've already worked can't be charged.

Map, log and settings

Drag the globe to spin it, and use Centre DX or Home QTH to re-centre. Open the station log and the hop table to look back at your calls. Settings covers quality, units, layers, sound and reduced motion.

Finishing and sharing

Work all ten stations, reach 24:00, or end the day yourself. The results show your paths, score, best DX and a tip for next time, and you can copy or share them if your browser allows it.

Keyboard and touch

Use 1-9, 0 and - for the bands in the order shown, and C to call. The right arrow moves the clock on ten minutes and the up arrow one hour. Shortcuts don't fire inside form fields, open dialogs or with modifier keys held. On a phone, tap Radio desk to open the bottom sheet; it scrolls on its own.

Scoring

Base points are the distance in kilometres divided by 100 and rounded, then multiplied by rarity, mode and power. The mode multipliers are FT8 1.0, CW 1.5 and SSB 2.0. The power multipliers are 5 W 3.0, 50 W 1.5, 100 W 1.0 and 400 W 0.7. A grey-line contact adds 20%, and then any hints you bought come off that contact only. The distance units in Settings change what's shown, not the score.

Each confirmed QSO shows the sum on a card, for example 113 × 4 × 1.5 × 3 = 2,034 for an 11,347 km CW contact at 5 W with a rarity 4 station. Hints show as a minus percentage, such as − 10% hints. A comet runs along the path to the station and your score counts up. With reduced motion on, in Settings or on your device, you get the card and the new score straight away.

Five starter tips

Try the low bands after dark, and the higher bands by day when the SFI is high.
For a station a few hundred kilometres away, try a low dipole on 40m.
When the signal is above the MUF, go lower in frequency. More power can't fix a hop that escapes.
Start with FT8 and 100 W to learn a route, then try less power or a higher-scoring mode on other stations.
Work the stations whose windows close early first. Waiting is useful, but you can't get time back.

The propagation bit

Skywave

Your signal leaves the Earth, refracts through a layer of the ionosphere and comes back down. Long routes may need several hops, with a ground reflection between each. The game models the short great-circle route, not the long way round.

The F2 layer

In the game, the F2 layer sits 300 km up. Its critical frequency rises with sunlight and solar flux, and falls during geomagnetic storms. It's drawn eight times higher than scale so you can see the geometry.

The D layer

The lower D layer soaks up energy rather than bringing your signal home. It's strongest in sunlight and hardest on the low frequencies. Every skywave hop crosses it twice, and a flare multiplies the sunlit loss by five.

MUF

The maximum usable frequency is the highest frequency that works on a given path. Each hop has its own limit, based on its midpoint and length. The lowest hop MUF sets the limit for the whole route; above it, the signal escapes.

LUF

The lowest usable frequency is the practical bottom edge of an opening. The game doesn't give a single LUF figure. It checks whether absorption and noise leave enough signal to decode. More power or a more sensitive mode can help at the bottom edge, but not above the MUF.

Skip distance and the skip zone

A skywave signal can come down beyond a nearby station instead of at it. Ground wave only covers a short distance in the game. When a short route is out of ground-wave range and can't work by NVIS, it's in the skip zone.

NVIS

Near-vertical incidence skywave sends energy steeply upwards to reach nearby stations. In the game, routes under 500 km need a frequency below the overhead F2 critical frequency and an antenna with high-angle radiation. A low dipole is a good start; a low-angle vertical isn't.

The grey line

The grey line is the boundary between day and night. In the game, both ends need the sun between 6 degrees below and 6 degrees above the horizon. On 160m to 30m, that gives 4 dB more signal and a 20% scoring bonus on a successful contact.

Solar flux (SFI)

The SFI is the day's solar flux figure for the model. Higher values raise the F2 critical frequency, which often opens the higher bands. It doesn't mean every high-band path is open.

K and A indices

K is the geomagnetic activity for the game day, from 0 to 7. A is a daily figure worked out from K, not a separate penalty. High K pushes the modelled F2 layer down, raises the noise and adds loss on polar paths.

Sporadic E

On northern-summer dates, daily or practice, up to three localised patches of E layer can appear. A single-hop route of 500 to 2,200 km on 10m or 6m can open if its midpoint is inside an active, sunlit patch. The conditions screen lists the patch centres, sizes and UTC times.

Take-off angle

Take-off angle is the elevation at which your signal leaves the antenna. Longer hops usually use lower angles; nearby skywave contacts need steep ones. The geometry uses a 300 km F2 height and a 3-degree minimum, which gives a longest hop of about 3,225 km in the game.

Choosing an antenna

A low dipole favours NVIS, and the half-wave-high dipole suits medium angles. A vertical favours low angles, and the EFHW has a simplified, slightly weaker dipole-like pattern. The magnetic loop trades gain for less local noise, and the Yagi adds directional gain on its own bands only.

Aiming the Yagi

The Yagi covers 20m to 10m, including 17m and 12m. Use the bearing control to point it at the station, or press Aim at the DX. Off the beam you lose gain, and the modelled rear is 20 dB down on the front.

FT8

FT8 is the most sensitive mode in the game and decodes at -20 dB SNR. Its mode multiplier is 1.0. The warble you hear is a sound effect, not a real FT8 signal.

CW

CW uses Morse-like tone bursts and decodes at -10 dB SNR in the game. Its mode multiplier is 1.5, so it sits between FT8's sensitivity and SSB's score.

SSB

SSB is the least sensitive mode and needs +6 dB SNR. It earns a 2.0 multiplier but isn't allowed on 30m. The radio noise you hear is an effect, not recorded speech.

QSB and decode margin

A signal only 0 to 3 dB above its decode threshold is marginal. Each marginal call has a seeded 50% chance of decoding, and both success and failure show QSB, so a narrow miss can be fading rather than a closed path.

Beyond the game

For real propagation planning, use VOACAP Online , and for what's actually being heard, DX cluster maps . Skywave doesn't check local allocations, licensing, station permission or interference, and its frequencies are game inputs, not operating advice.

Tell me what I got wrong

Spotted something a real operator would wince at? Email me: hello@dexmlabs.app. 73, Arthur