📻 radio ES
UTC --:--

Step 2

Understand

How radio travels, what the bands are, what propagation is like today and when the Space Station passes over you.

5-minute lessons

How radio works

Four ideas that explain almost everything. Choose how deep you want to go: the same lesson told for the curious, for the keen, or with the technical bits.

Making sense of what you hear

The bands: a map of the spectrum

Radio amateurs have reserved “lanes” in the spectrum. They're named after their wavelength. Tap a band to see how it behaves.

Approximate ranges for IARU Region 1 (Europe and Africa). Exactly what you can use depends on your authorisation (autorización).

The weather… but in space

What's propagation like today?

The Sun is in charge. With lots of solar activity the high bands “open up” and you can reach incredibly far; with geomagnetic storms everything goes quiet. Radio amateurs check it the way you'd check the forecast before heading into the hills.

Checking the Sun…

The ionosphere map, right now

World map of the maximum usable frequency at this moment

Each colour is the highest frequency (in MHz) that bounces back in that area for a 3,000 km hop. Where it says 28 or more, the 10 m band is open. Map by KC2G, updated every 15 minutes.

How to read it

Solar flux
The higher it is, the better the high bands work (20, 15, 10 m). Above 150 it's a party.
K index
How stirred up the magnetic field is. 0–2 calm; 5 or more, a storm: noise and closed bands.
Day / Night
By day the high bands work; by night the low ones (80 and 40 m). That's why the dial on the home page changes with the time.
Solar cycle
The Sun goes through cycles of about 11 years. Cycle 25 peaked recently: a good time to start.

Check propagation with your own ears

The beacons, right now

Eighteen beacons around the world take turns, every 3 minutes, on five shortwave frequencies: their callsign in Morse and four dashes getting weaker (100, 10, 1 and 0.1 watts). If you hear the Japanese one on 20 metres, the band is open towards Japan; if you hear even the last dash, a tenth of a watt would get you there.

--:--:-- UTC
FrequencyOn the air nowListen

The NCDXF/IARU beacon network, synchronised by GPS: the schedule is worked out in your browser from the time. The button opens the Twente receiver already tuned in CW; if you can’t hear the beacon, that band isn’t open from Europe towards it.

Radio from space

When does the Space Station pass over you?

The ISS carries an amateur radio station. When it passes overhead, for about 10 minutes, you can hear it with a walkie-talkie or a simple receiver on 145.800 MHz FM. Here you can see where it is now and its next passes.

Calculating the orbit…

Showing passes for Madrid. Your location is only used in your browser: it isn't sent anywhere.

Next passes

    Orbit from CelesTrak, calculated in your browser. With a handheld antenna and some patience you can hear the school contacts arranged by ARISS; high passes are easier to hear. As it approaches and moves away, the frequency shifts by a few kHz (the Doppler effect).

    Beyond the ISS

    Amateur radio satellites

    There are dozens of satellites built by and for radio amateurs. These are the two easiest ways in from Spain.

    📡 QO-100 · the satellite that never moves

    Es’hail-2, 36,000 km above the equator at 25.9° East: always at the same point in the sky and visible from Europe, Africa, the Middle East and parts of Asia, Brazil and India. It carries the first geostationary amateur transponder.

    • To listen (no licence needed): a 60–80 cm TV satellite dish, an LNB and an SDR receiver. The narrowband downlink runs from 10489.500 to 10490.000 MHz, with beacons at both ends and in the middle.
    • To transmit: uplink on 2400.005–2400.490 MHz. In Spain that band is authorised for radio amateurs on a temporary, experimental basis until 26 December 2026 (2400–2410 MHz, maximum 1500 W EIRP, directional antenna of at least 21.5 dBi, no interference).
    • Without any kit: there are web receivers for QO-100 you can hear in your browser, such as the BATC one.

    Sources: AMSAT-DL band plan and URE: 2.4 GHz authorisation (in Spanish). Web receiver: BATC.

    🛰️ FM satellites: a flying repeater

    They pass for 10–15 minutes and repeat in FM whatever they receive. With a dual-band handheld and a handheld directional antenna (an Arrow or a home-made Yagi) you can make contacts hundreds of kilometres away. To listen, any receiver on the downlink frequency will do.

    SatelliteUplinkDownlink
    SO-50145.850 MHz · 67.0 Hz tone436.795 MHz
    AO-91
    battery worn out: sunlight only    		435.250 MHz · 67.0 Hz tone145.960 MHz
    ISS145.990 MHz · 67.0 Hz tone437.800 MHz

    Next useful passes from Madrid

    1. Calculating…

    Uses the location chosen above for the ISS. Only passes higher than 10°. Because of the Doppler effect, the 70 cm downlink shifts by about ±10 kHz: start a little high and tune down during the pass. Status and frequencies: AMSAT.