Ham Radio SSTV: Send and Receive Pictures Over the Air

Ham radio SSTV, short for slow-scan television, lets you send and receive still pictures over the air using nothing more than a normal transceiver, a computer sound card and decoding software that most hams already have the skills to set up. A picture takes a minute or two to arrive, line by line, and watching it build on the screen is one of the most satisfying experiences in amateur radio. This guide explains how SSTV works, which modes are common, where to find activity, what software and cabling you need and how to avoid the mistakes that produce a smeared or slanted image.

SSTV also has a special place in space communication, since astronauts and the people behind the ISS programme have sent images from orbit to amateurs on the ground. That makes it one of the few modes where a simple FM handheld and a basic antenna can produce a picture from space.

A Short History

The concept of slow-scan television was introduced by Copthorne Macdonald in 1957 and 1958. His first system used an electrostatic monitor and a vidicon camera tube, and it was found sufficient to use around 120 lines and 120 pixels per line to send a black-and-white still picture within a 3 kHz telephone channel. The first live tests were made on what was then an amateur band. Early SSTV needed specialised equipment, typically a scanner or camera, a modem that created the characteristic audio sound and a cathode-ray tube with long-persistence phosphors that kept the picture visible for around ten seconds.

Today the system is much simpler. As the overview of slow-scan television describes, a modern system, which gained ground from the early 1990s, uses a personal computer and special software in place of the custom equipment. The sound card acts as a modem, the computer screen provides the output and a digital camera or stored photographs provide the input.

How SSTV Works

SSTV is an analogue mode. It uses frequency modulation of an audio tone: every different value of brightness in the picture gets a different audio frequency. Brighter pixels are sent as a higher tone, and darker pixels as a lower one. The brightness values lie between roughly 1500 and 2300 Hz, and sync pulses use 1200 Hz. Colour is sent by transmitting the brightness of each colour component, normally red, green and blue, one after another on each line. The audio signal is then fed into an SSB transmitter, which places it in the radio spectrum.

A picture begins with a calibration header, which tells the receiving software what is coming. The header consists of a 300 millisecond leader tone at 1900 Hz, a 10 millisecond break at 1200 Hz and another 300 millisecond leader tone at 1900 Hz. A digital VIS code, made of 30 millisecond bits, follows. It identifies the mode in use, so that modern decoding software can switch to the right settings automatically. After the header, the image is sent as horizontal lines, scanned from left to right, with the colour components of each line sent separately.

Because the modulation is analogue, there is no error correction. A burst of noise or a fade shows up as a streak across the picture, not as a missing character. That is part of the charm: even a poor signal produces something, and a lucky picture can look surprisingly good.

Common SSTV Modes

There are many SSTV modes, with different durations, resolutions and colour methods. A longer mode usually gives a better picture but takes longer and is more affected by fading. The most common modes in everyday use are:

The Martin and Scottie families are the ones you will hear most often on HF, where Martin M1 is popular in Europe and Scottie S1 is used mostly in the United States. Some black-and-white modes take only around eight seconds to send an image, which is convenient for quick tests. For a first attempt, choose Martin M1 or Scottie S1 and use whichever matches the stations you can hear.

Where to Find SSTV Activity

SSTV can be heard on HF, VHF and UHF. On HF, activity clusters on a handful of well-known frequencies. Using a receiver capable of demodulating single sideband, the overview of the mode lists the following common frequencies:

• 80 meters: 3.845 MHz, or 3.73 MHz in Europe, LSB.
• 40 meters: 7.171 MHz, or 7.165 MHz in Europe, LSB.
• 20 meters: 14.230 MHz, the main calling frequency, USB, with 14.227 and 14.233 MHz used to relieve crowding.
• 15 meters: 21.340 MHz, USB.
• 10 meters: 28.680 MHz, USB.

Band plans differ between regions, and a frequency that is correct in one country may sit inside another band segment in a different country. Always check your regional plan before you transmit, for example with our guide to the IARU band plan regions. The 20 meter calling frequency is the best place to start, because it has the most activity, especially during daylight.

There is also SSTV activity on VHF FM, including from the International Space Station. The programme known as ARISS, Amateur Radio on the International Space Station, has run SSTV events in which images are transmitted from the station on 145.800 MHz FM. In one published event announcement, the images were sent in PD120 mode, the event ran for about a week, and participants who decoded images could submit them to a gallery and request an electronic certificate within a set time after the event ended. Dates and details change from event to event, so check the ARISS SSTV events page for the latest schedule.

What You Need to Get Started

SSTV needs no special radio. A transceiver capable of SSB on HF, or FM on VHF, will do, together with a way to get audio between the radio and a computer.

Software

Many free and commercial programs decode and encode SSTV. The overview of the mode names MMSSTV for Windows, QSSTV for Linux and MultiMode for the Mac among those in use, along with Ham Radio Deluxe on Windows. For phones, there are Android apps such as Robot36 for decoding and others for encoding and decoding on both Android and iOS. A phone running a decoder placed near a speaker is a quick way to receive your first picture, though it is a workaround, not an ideal setup.

Audio interface

A computer sound card acts as the modem, so you need audio from the receiver to the computer, and audio from the computer to the transmitter. Many modern transceivers have a built-in USB audio interface. Older radios need an external interface or a cable to the microphone and speaker connections. The wiring and level principles are the same as for the other sound-card modes, and our guide to setting up fldigi with a sound card and rig control walks through them. For general sound-card digital operation, also see our comparison of digital modes beyond FT8.

Mode and sideband

Set the radio to the correct sideband for the band. By the convention in the frequency list above, SSTV on 80 and 40 meters uses lower sideband, and on the higher HF bands it uses upper sideband.

Your First Picture: Receiving

1. Tune to a known frequency. Start on 14.230 MHz during the day, in upper sideband.
2. Connect the audio. Make sure the computer is receiving audio from the radio at a sensible level, neither too low nor clipped.
3. Choose the receive mode. Most programs can detect the mode from the VIS code. If not, select Martin M1 or Scottie S1 manually.
4. Listen. An SSTV signal sounds like a series of warbling tones with a rhythmic pulse. When you hear one, the software should begin drawing the image.
5. Save the result. Even an imperfect image is worth saving, and comparing different bands and times of day is part of learning.

A slanted picture means the sample rate or the timing is slightly off. Most programs have a slant correction feature. A picture with horizontal streaks usually points to noise or fading.

Your First Picture: Transmitting

1. Prepare an image. Use a clear photograph or a station card with a few large elements. Fine detail is lost at the resolutions used.
2. Add your call sign. A call sign overlay in the picture is a common and helpful practice. Follow the identification rules of your licence in addition.
3. Set the audio level. Keep the audio drive moderate, with little or no ALC action. Overdriving the transmitter distorts the tones and widens the signal.
4. Listen first. Check that the frequency is clear before you send.
5. Send at modest power. SSTV is a continuous-tone mode, and a transmitter that cannot handle a high duty cycle may overheat.

Because every picture takes one to two minutes or longer, you should expect the transmitter to be keyed for the whole duration, and the same care applies as for any digital mode. Run the transmitter at a conservative power level and make sure the cooling is adequate.

Operating Practices and Courtesy

• Do not transmit on top of an image in progress. Wait until the picture ends, then call.
• Identify yourself. A voice call before or after the picture, or an overlay, tells others who you are.
• Share conditions. A short voice report on how a picture looked helps the sender improve.
• Move off busy channels for long conversations. Agree on a nearby frequency to keep the calling channel clear.
• Keep the content appropriate. Amateur rules apply to pictures, just as they do to voice.

Antennas, Power and Band Conditions

SSTV is forgiving about antennas, but it rewards a clean signal. Any antenna that works for SSB on the chosen band will work for pictures. The difference is that an image takes a minute or two to arrive, so it suffers more than a short voice call when the signal fades. For that reason, SSTV does best when the band is stable: daytime on 20 meters is the classic example, and the calling frequency is usually busiest when the band is open to several continents.

Power does not need to be high. Because the mode is a continuous tone, a moderate power level with a clean signal is better than maximum power with distortion. Use only as much power as you need for a readable picture, keep the audio level moderate and check that your transmitter is happy with a full transmission of a minute or more. The same discipline applies to other sound-card digital modes.

If your first pictures are poor, change one thing at a time. Try a different time of day, a different band and a different mode. Pictures that fail on one path often succeed on another, and the only way to learn what works from your location is to try.

Common Problems

• Slanted image. Adjust the slant correction or the sound card sample rate.
• Noisy lines or streaks. Poor propagation, atmospheric noise or fading. Try a different time or band.
• Wrong colours or stripes. Wrong mode selected, or a timing error.
• Images stop mid-way. The header was missed or the signal faded. Wait for the next transmission.
• Distorted transmit signal. Audio drive too high. Reduce it until the ALC stays quiet.

The Bottom Line

SSTV turns the sound card in your computer into a window onto the radio spectrum. It works with any SSB transceiver, uses simple software and has a long history of making amateur radio visible. Start by receiving on 14.230 MHz with Martin M1 or Scottie S1, learn how headers and modes work, then try sending a clear, simple image with your call sign. Keep the audio clean, respect the band plan and watch for ISS events if you want to see a picture from space. A few evenings of experiment will give you a skill that few hams ever try.

Frequently Asked Questions

What is the most common SSTV frequency?

On HF the main calling frequency is 14.230 MHz on 20 meters in upper sideband, with 14.227 and 14.233 MHz used to relieve crowding. Check your regional band plan before transmitting.

How long does an SSTV picture take?

It depends on the mode. Martin M1 takes about 114 seconds and Scottie S1 about 110 seconds, while PD120 takes about 126 seconds. Some black-and-white modes need only around eight seconds.

What software do I need for SSTV?

A sound card program such as MMSSTV on Windows, QSSTV on Linux or MultiMode on the Mac. Android and iOS apps can also decode or encode images.

Can I receive SSTV from the ISS?

Yes, during ARISS SSTV events. Images have been transmitted from the station on 145.800 MHz FM in the PD120 mode. Check the ARISS events page for dates and details.

Which sideband is used for SSTV?

Lower sideband on 80 and 40 meters, and upper sideband on the higher HF bands, following the usual convention.

Why is my SSTV picture slanted?

The timing of the received lines is slightly off, usually because of a sample-rate difference between the transmitting and receiving sound cards. Use the slant correction in your software.