SSTV pictures

SSTV needs APRS Connect Pro. It works in the Android app so far.

Slow scan TV (SSTV) sends a picture as sound: one tone whose pitch is the brightness and color of each point, line by line. A picture takes from half a minute to a few minutes. The International Space Station sends SSTV pictures during ARISS events, on 145.800 MHz FM, and anyone with a radio that receives 2 m FM can pick them up.

The SSTV screen is in the drawer.

Listening

Press Listen. The app listens for a picture and draws it line by line as it arrives. The line under the button says what it is doing: listening, or the mode and how many lines have arrived. The bar under it is the input level: it should move with the radio's sound.

There are two ways to get the radio's sound into the phone:

• Hold the phone near the radio's speaker. No cable is needed, and it is how most people receive the ISS. Keep the phone still and the room quiet, and set the radio's volume so the tones are clear but not distorted.
• A cable, the same one the audio modem uses. If an audio channel is running, SSTV listens through its input automatically, and the screen says so. Otherwise pick the input under Listen through, in the settings behind the gear at the top of the SSTV screen: Automatic, the phone's microphone, or the cable or USB sound card while one is plugged in.

The screen stays on while it listens. Listening carries on if you switch to another app: Android then shows a notification, APRS Connect is receiving SSTV, for as long as it listens, because only an app that shows one may use the microphone in the background. Listening stops when you press Stop or leave the SSTV screen. A picture that was coming in is kept with the lines that arrived.

The mode

SSTV has many modes, which differ in picture size, speed and how color is sent. Auto reads each picture's mode from the short header sent before it. Auto also picks up a picture that is already under way when you start listening, or when the ISS comes over the horizon: it recognises the mode from the rhythm of the picture's lines and starts from the line it joined at, so the top of that picture is missing. SSTV does not send line numbers, so for such a picture the screen says how many lines have arrived rather than which line it is on, and the picture ends a few seconds after its lines stop.

On a weak or rough signal, a picture found this way is shown only once its lines have kept time for a few seconds, so noise that looks like the start of a picture does not flash up on the screen.

To decode every picture as one mode, pick that mode instead of Auto. That is for a sender that leaves the header off, or a header lost in noise. A picture sent in another mode then comes out as noise, so go back to Auto when you are done.

The modes the app knows are Robot 36 and 72, Martin 1 and 2, Scottie 1, 2 and DX, and PD50, PD90, PD120, PD160, PD180, PD240 and PD290. The ISS sends PD120, and sometimes PD180.

A sound card that runs a little fast or slow makes a picture lean. The app measures that from the picture itself and straightens it, so there is nothing to set.

Received pictures

The SSTV screen has three tabs: Receive, Send and Gallery. Receive shows the last three pictures under the live one, and All pictures opens the rest. Gallery lists every picture kept, by day, newest first. Tap one to see it full width with its mode, time, how many lines arrived and, if it came in during an ISS pass, how high that pass went. Swipe for the next one.

This list is for looking at what you received lately, not for keeping pictures. Pictures in the gallery clear after 30 days. A picture not yet saved says how many days it has left. To keep one, save it to the phone's photos. The buttons along the bottom of an open picture are:

• Save puts it in the album APRS Connect SSTV in the phone's photos. To sort pictures further, move them in the phone's Gallery app.
• Share sends it to another app, for example to post it to the ARISS SSTV gallery.
• Delete takes it off the list, with its recording.

Save every complete picture, in the settings behind the gear, saves each complete picture to that album as it arrives. It is off at first.

Recordings

The app also keeps each picture's sound, from a few seconds before the picture to ten seconds after it, which is where a sender puts their callsign. An open picture has a small player for it: the play button plays it through the phone, and the bar shows how far it has got. Leaving the picture stops it. The ⋮ beside it has:

• Save to the phone, which puts it in the folder APRS Connect SSTV, in the phone's Recordings (Music before Android 12).
• Share, which sends it to another app, for example to decode it again in a program on a computer.

A recording is kept as long as its picture and goes when the picture is deleted or clears. It takes about 1.5 MB a minute. To stop recording, switch off Record each picture's sound in the settings behind the gear. It is on at first.

Groups and senders

The list groups pictures for you: the chips above it show all of them, only those received during an ISS pass, or those from one sender.

Many SSTV programs send the sender's callsign in Morse code (CW) just before a picture, just after it, or both. The app listens for it whenever a picture is not coming in, and reads it as it arrives:

• On the Receive tab, while the app listens, Sent by under the picture fills in with the callsign as it is read, and the line under it shows what was heard. You can type a callsign there instead, at any time. One you type stays for every picture until you change it, which suits an ISS event, where every picture comes from RS0ISS. One read in CW counts for its own picture only.
• After a picture, the app listens for ten more seconds. A callsign read then fills in that picture's Sent by, unless one was typed.

Each picture is filed under its sender, and an open picture shows what was heard in CW under Sent by. If the app heard nothing, or the wrong thing, type the callsign there. A callsign you typed is never replaced.

Received pictures and their recordings are not in the app's backup and do not sync between devices. The phone's photos are where they are kept.

Sending pictures

The Send tab sends a picture of your own. Only transmit where your license allows it.

1. Pick the picture.

   • Photos opens the phone's photo picker.
   • Camera opens the phone's camera app.
   • Received shows the pictures you received; tap one to send it back. An open picture also has a Send button at the bottom.
   • Card is a plain colored card with only your text on it. Pick its color under it.

   The app needs no permission for either the photos or the camera: Android's own picker and camera app hand it the one picture you chose.

   A photo fills the picture at first, cut to the mode's shape around its middle.

2. What goes on it. Your callsign puts your callsign at the top, and Your line adds a line of your own at the bottom, for example a signal report. The picture at the top of the tab is exactly what goes out.

3. Edit it, if you like: tap the picture, or Edit on it, to open it full screen. The tools along the bottom:

   • Photo moves the photo under the picture: drag it so heads and text stay in, pinch to zoom, double-tap to fill again. The part of the photo outside the picture shows dimmed round it, so you can see what is cut off. Zoom out to see the whole photo, with black where it does not fill the picture.
   • Move picks up anything on the picture, your callsign and your line included: tap it, then drag it, or pinch it bigger or smaller. The colors and sizes under the picture then change it, and the bin deletes it. In any tool, you can also hold your finger on something for a moment, until the phone buzzes, and then drag it.
   • Text: tap where it goes and type, right on the picture. Tap a text to change its words; your line's words are Your line on the Send tab, and your callsign's are in Settings.
   • Pen draws, and Marker draws wide and see-through, like a highlighter.
   • Box covers part of the picture: drag to draw it. Black is for hiding something.
   • Sticker puts an emoji on the picture, large, in the middle, ready to drag where it goes. Its size can be changed like a text's. You can also type an emoji into a text from the keyboard.

   Pick a color and a size under the picture before you draw. Undo and Redo are at the top. Done keeps what you did, and the cross leaves the picture as it was. Markup stays where you put it on the picture, even if you move the photo under it afterwards. Thin lines and small text blur on the air, so the sizes start where they still read.

4. The mode. Pick it as on the Receive tab. Robot 36 is the quickest, at 36 seconds; the line under Transmit says how long the one you picked takes.

5. Transmit. The app asks first, saying how long it takes and where the sound goes:

   • With an audio channel running, through its cable, and its PTT (or the radio's VOX) keys the radio, as for a packet.
   • Otherwise through the phone's speaker. Hold the phone to the radio's microphone and key the radio yourself, or use its VOX.

   The screen shows how far it has got. Stop stops it at once.

After each picture the app sends your callsign in Morse code (CW), which many countries require and which other programs read to fill in who sent it. To turn it off, switch off Send your callsign in CW after each picture in the settings behind the gear.

Transmit needs your callsign in Settings. A placeholder such as N0CALL cannot transmit.

Saving a picture as sound

Save as sound makes the same sound as Transmit, picture and CW ID, as a file instead. Save to the phone puts it in the folder APRS Connect SSTV in the phone's Recordings (Music before Android 12), and Share sends it to another app. It needs no callsign.

On HF

SSTV on HF is sent in upper sideband (USB), most of it around 14.230 MHz on 20 m. Set the radio to USB and receive and send exactly as on FM: the app works on the radio's audio, which carries the same tones either way.

On sideband, a dial a little off the sender's moves every tone, which would make a picture darker or brighter, tint its colors, and past about 100 Hz lose the mode header. The app measures how far off each picture is as it starts, from its header, and corrects for it, up to 250 Hz either side. A picture joined partway, without its header, is corrected from its sync pulses, which works up to about 100 Hz off. Tune by ear as close as you can, and leave the rest to the app.

When sending on HF:

• Set the audio level so the radio's ALC barely moves. Too much drive distorts the tones.
• SSTV keeps the transmitter keyed for the whole picture, two minutes in PD120. Many radios are not built for that at full power, so turn the power down.

Receiving the ISS

The sky chart beside the picture

Switch on ISS sky chart, in the settings behind the gear at the top of the SSTV screen, to see where the station is while a picture comes in: the same chart as a pass on the ISS screen, with the live dot and, on a phone, the compass. It sits above the picture on a phone held upright, and beside it on a phone turned on its side or a tablet. Its top line says how high the station is, in which direction, whether it is rising or setting and how long it has left, or when the next pass is. It is off at first.

Open SSTV from the ISS screen, or from a pass with Receive SSTV, and the chart shows whatever the switch says, for that pass. The arrow beside it shrinks it to its top line, to leave more room for the picture, and the cross closes it, the same as switching ISS sky chart off.

Tips

• ARISS announces SSTV events a few days ahead. Outside an event the ISS sends no pictures.
• Tune the radio to 145.800 MHz FM. The ISS uses wide FM, so pick the wide filter if the radio has a choice. Leave the squelch open, so a weak start of a picture is not cut off.
• The ISS screen lists the next passes. A pass high in the sky gives the best pictures; one low on the horizon may give part of one.
• A picture takes about two minutes in PD120, so a pass of ten minutes carries about three.

What it does not do yet

• It works in the Android app only. The iPhone, desktop and browser apps do not receive or send SSTV yet.
• It reads a callsign sent in CW, but not one sent as FSK, the short burst of two tones some programs use instead, and it sends CW, not FSK.
• It cannot send through a radio's Bluetooth audio yet.

Last updated 18 October 2026