Work the ISS from your backyard.

The International Space Station carries an amateur radio station — and astronauts use it. With a Technician license and a $30 handheld you can talk through its repeater as it flies over San Diego at 17,000 mph. Here's when to point your antenna up.

NEXT PASS OVER DM12 · SAN DIEGO

--:--:--UNTIL AOS · ACQUISITION OF SIGNAL

MAX ELEVATION

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DURATION

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PATH

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UPCOMING PASSES · LOCAL TIME

DATE	AOS RISES	MAX EL PEAK	DUR MINS	QUALITY
COMPUTING ORBIT…

FETCHING CURRENT ORBITAL ELEMENTS…

SKY PATH · NEXT PASS

ISS FREQUENCIES

Voice downlink — what the ISS transmits, worldwideListen here. Receiving needs no license at all.145.800

Voice uplink — what you transmit, the AmericasEurope and Africa use 145.200 instead.144.490

Repeater input — you transmit hereNeeds a 67.0 Hz CTCSS tone or it will not open.145.990

Repeater output — you listen hereDifferent band from the input, hence "crossband".437.800

APRS digipeater — short text, no voiceTransmit and listen on the same frequency.145.825

SSTV — pictures, during events onlyRobot 36 mode. Some older events used 145.800.437.550

HOW TO WORK IT

Three steps to a space contact

STEP 01

Get your Technician license

All you need to transmit on the ISS bands. SANDARC exams are free — most people pass with a weekend of study. You need no license at all to listen, so you can start tonight.

STEP 02

Grab any dual-band handheld

A $30 handheld and its stock antenna will hear the ISS. A $25 handheld Yagi — a small directional antenna you point by hand — is what makes the crew's repeater hear you.

STEP 03

Work the pass

Wait for a pass above about 30°, listen first, then call. The full sequence is below — it is shorter than it looks.

THE PASS, START TO FINISH

Pick a good pass. Use the table above. Anything under about 30° max elevation is a scrape along the horizon; a 60°+ pass gives you roughly ten minutes and a much better shot. Passes come in clusters, then nothing for hours.
Decide what you are working. Three different things share the station, and only one of them is a person:
- The repeater — a machine that hears you on 145.990 and repeats you on 437.800. On air whenever the crew has it enabled. This is the realistic first contact.
- APRS — a packet digipeater on 145.825 that bounces short text messages. No voice, no crew involvement, works on almost every pass.
- The crew — on 145.800. Astronauts mostly run scheduled contacts with schools; casual chats happen, but they are luck, not a plan.
Set the radio up before the pass. For the repeater, program a split: transmit 145.990 with a 67.0 Hz CTCSS tone, receive 437.800. Without that tone the repeater will simply ignore you.
Correct for Doppler. The station is closing at about 7 km/s, so its signal arrives high as it rises and low as it sets — the same effect that drops the pitch of a passing siren. On 437.800 that is roughly ±10 kHz: start about 10 kHz high, step down through the pass, end about 10 kHz low. On 145.800 it is only about ±3 kHz, so listening on 2 m needs little or no correction.
Listen before you transmit. A pass is a shared, crowded resource. If you hear a contact in progress, wait for it to finish.
Call short. Say your callsign and grid square — "KK6XYZ, DM12" — then stop and listen. Long calls waste a pass that lasts minutes for everyone watching it.
Log it and try again. Most people miss several passes before their first contact. That is normal, and it is most of the fun.

Frequencies and repeater status come from ARISS, the volunteer group that runs amateur radio aboard the station. The crew reconfigures the radio from time to time — if nothing is heard on a strong pass, check there.

PLAIN ENGLISH

The words on this page

AOS / LOS: Acquisition of signal and loss of signal — the moments the station clears your horizon and drops back below it. The beginning and end of a pass.
Pass: One trip across your sky. The ISS orbits every ~90 minutes, but only some orbits come over you.
Elevation: How high above the horizon, in degrees. 0° is the horizon, 90° is straight overhead. Higher passes are longer and far easier to work.
Azimuth: Compass direction, in degrees. 0° is north, 90° east, 180° south, 270° west.
Uplink / downlink: Uplink is what you transmit up to the station; downlink is what it transmits back down to you.
Crossband repeater: A repeater that listens on one band and retransmits on another — here, up on 2 m and back down on 70 cm — so it can hear and talk at the same time.
CTCSS / PL tone: A quiet sub-audible tone sent alongside your voice that tells a repeater the transmission is meant for it. The ISS repeater needs 67.0 Hz.
Doppler shift: The apparent change in frequency caused by the station's speed toward or away from you — the siren effect, applied to radio.
APRS: Automatic Packet Reporting System — short data messages rather than voice. The ISS relays them like a mailbox in orbit.
SSTV: Slow-scan television — still pictures sent as audio. During SSTV events the station transmits images a free phone app can decode.
Handheld / HT: A handheld transceiver: a walkie-talkie style radio. "Dual-band" means it covers both 2 m and 70 cm.
2 m / 70 cm: Ham shorthand for the two bands used here, named by wavelength: 2 m is around 145 MHz, 70 cm around 437 MHz.
Yagi: A directional antenna — the classic "TV aerial" shape. Pointing one at the station beats a stock rubber antenna by a wide margin.
Grid square: A short location code used instead of an address. San Diego is DM12. Hams trade them because they are quick to say over a noisy link.
Callsign: The unique identifier the FCC issues you, like KK6XYZ. You must say it when you transmit.
Orbital elements / TLE: A two-line element set: the numbers describing the station's orbit, which this page fetches to work out when it passes over you.
73: Ham shorthand for "best regards" — the traditional sign-off.