Extensions

🇫🇷 Version française

Extensions: SDR dongle, FT8/FT4, radiosondes

Beyond satellite passes, SatMe carries a few receivers of its own. They are all open from the ⋮ menu, with nothing to unlock.

RTL-SDR dongle

SatMe drives an RTL-SDR dongle plugged into the phone's USB-C port directly, with no other app: it corrects the receive Doppler, plays the sound on the phone loudspeaker (or headphones) and decodes SSTV.

With a 137 MHz antenna it also decodes the METEOR-M2-3 / M2-4 weather pictures (from 20.82, beta): see METEOR pictures.

Hardware: an RTL2832U dongle with an R820T or R820T2 tuner (most RTL-SDR and DVB-T sticks), a USB-C OTG adapter and a reasonable antenna — a dongle with no antenna hears nothing.

1. Open SDR dongle from the ⋮ menu (it also appears on a satellite's page as soon as a dongle is plugged in).
2. Plug the dongle in and accept the USB permission.
3. Tap Start receiving: SatMe tunes to the selected satellite's rest frequency (145.800 MHz, the ISS SSTV frequency, when none is selected) and follows the Doppler once a second.

Setting	What it does
Spectrum and waterfall	Touch the waterfall to tune; drag to follow a drifting signal
Receive mode	Narrow FM, USB, LSB, AM
Bandwidth · Squelch	Auto or by hand
Automatic Doppler tracking	On by default while the satellite is up
Tuner gain · Digital AGC	Automatic gain is fine most of the time; with a strong signal, a manual gain around 30 dB sounds cleaner
Crystal correction (ppm)	A few tens of ppm are normal on a cheap stick, several kilohertz at UHF
Record an MP3 · Decode SSTV	Into the same folder as pass recordings; pictures go to the SSTV page

The dongle can also be the receive side of a station whose FT-817 or IC-705 transmits: see Rig control (CAT). On QO-100, it shows the whole transponder and locks on the beacon.

FT8 / FT4 decoding

FT8 / FT4 decoding (⋮ menu) listens through the phone's audio input — microphone, or the rig's audio — and lists the messages decoded in each slot.

1. Set the rig's frequency and audio.
2. Tap Listen. Slots are aligned to UTC: your clock must be right to the second.
3. The first result comes at the end of the current slot. CQ only keeps the calls; Clear empties the list.

Error correction is on, so weak signals get through too — and a message failing parity or CRC is never shown: SatMe would rather miss than invent.

Radiosondes (beta)

Twice a day, every weather station releases a balloon that climbs to thirty kilometres, then comes down under a parachute. The sonde sends its position on the 400 MHz band: enough to follow it, and go and pick it up.

• Models: Vaisala RS41, Meteomodem M10 and M20.
• Band: 400.150 to 405.900 MHz, in 10 kHz steps; SatMe never goes above (distress beacons start there).
• Audio source: the SDR dongle (best), a USB sound card on the receiver's discriminator or headphone output, or the microphone in front of the loudspeaker (emergencies only).
• Nearest stations and their usual launch times, Automatic tuning (finds the signal's centre within ±25 kHz), position, altitude, speeds, GPS satellites.
• The flight: points received, Burst, descent, Estimated landing and its distance — a simple extrapolation of the last vector, with no wind model: check as you get closer.
• Logs of each flight are kept.

Tested on synthetic signals, not yet on a real balloon flight. A radiosonde test signal is in the settings.

Tips

• One USB-C port: an OTG hub lets the dongle share it with a rig's CAT cable.
• With the dongle there is nothing to wire for audio: the sound is made inside the phone.

See also: SSTV · Audio recording · QO-100