Transmission Time
Fast modes can transmit an image in less than one minute. Higher-quality modes may require several minutes.
SSTV Technology
🎨 SSTV Modes
Slow Scan Television uses several different transmission modes. Each mode determines how an image is converted into audio, how long the transmission takes and how much picture detail can be received.
Some modes are fast and suitable for short contacts, while others use longer transmission times to provide higher resolution and better image quality.
Image transmission formats
What Is an SSTV Mode?
An SSTV mode is a defined method for transmitting a still image using audio tones. It controls the order in which picture lines and colour information are sent.
The selected mode determines several important characteristics:
Image Resolution
Resolution determines how much detail can be displayed in the final decoded image.
Colour System
Different mode families transmit colour information in different sequences and formats.
Radio Conditions
A shorter mode may be useful during unstable propagation, while a longer mode can provide more detail when signals are reliable.
Automatic mode detection
How Does the Decoder Recognise the Mode?
Most analogue SSTV transmissions begin with a short identification sequence called a VIS code.
VIS means Vertical Interval Signalling. The code tells the receiving software which SSTV mode is being transmitted.
When the VIS code is received correctly, software such as MMSSTV, RX-SSTV or QSSTV can normally select the correct mode automatically.
When the beginning of a transmission is missed, the VIS code may not be received. The operator may then need to select the mode manually.
Quick comparison
Popular SSTV Modes
The following table compares several modes commonly encountered on amateur-radio frequencies. Transmission times are approximate.
| Mode | Family | Approximate Time | Typical Resolution | Typical Use |
|---|---|---|---|---|
| Martin M1 | Martin | 114 seconds | 320 × 256 | Popular general HF mode |
| Martin M2 | Martin | 58 seconds | 320 × 256 | Faster Martin transmission |
| Scottie S1 | Scottie | 110 seconds | 320 × 256 | Popular general HF mode |
| Scottie S2 | Scottie | 71 seconds | 320 × 256 | Faster Scottie transmission |
| Scottie DX | Scottie | 269 seconds | 320 × 256 | Long-distance and difficult conditions |
| Robot 36 | Robot | 36 seconds | 320 × 240 | Fast colour image transmission |
| Robot 72 | Robot | 72 seconds | 320 × 240 | Improved Robot image quality |
| PD50 | PD | Approximately 50 seconds | 320 × 256 | Fast PD transmission |
| PD90 | PD | Approximately 90 seconds | 320 × 256 | Balanced speed and quality |
| PD120 | PD | Approximately 2 minutes | 640 × 496 | High-resolution images and ARISS events |
| PD180 | PD | Approximately 3 minutes | 640 × 496 | High-quality detailed images |
Important:
Transmission times can vary slightly depending on the software,
timing implementation and mode variant.
Widely used on HF
Martin Modes
The Martin family is extremely popular among European SSTV operators. Martin modes provide good colour reproduction and reliable image quality.
Martin M1
Martin M1 offers a good balance between transmission time and picture quality. It is one of the most frequently heard modes on HF.
Time
Approximately 114 seconds
Resolution
320 × 256
Colour
Full colour
Best for
General HF contacts
Martin M2
Martin M2 transmits the same general image dimensions in roughly half the time of Martin M1.
The faster transmission can be useful when conditions change rapidly, although image quality may be more affected by noise.
Time
Approximately 58 seconds
Resolution
320 × 256
Colour
Full colour
Best for
Shorter HF transmissions
Popular worldwide
Scottie Modes
Scottie modes are widely used around the world. Their synchronisation structure differs from Martin modes, but the completed images have similar dimensions.
Scottie S1
Scottie S1 is one of the most commonly used SSTV modes. It provides good detail and colour in a transmission lasting just under two minutes.
Time
Approximately 110 seconds
Resolution
320 × 256
Colour
Full colour
Best for
General SSTV contacts
Scottie S2
Scottie S2 offers a shorter transmission time than S1. It is useful when operators want to exchange images more quickly.
Time
Approximately 71 seconds
Resolution
320 × 256
Colour
Full colour
Best for
Faster image exchanges
Scottie DX
Scottie DX uses a much longer transmission time. The slower scan can provide useful results during difficult long-distance reception.
Time
Approximately 269 seconds
Resolution
320 × 256
Colour
Full colour
Best for
Long-distance SSTV
Fast and historically important
Robot Modes
Robot modes are among the oldest widely supported colour SSTV formats. Robot 36 remains popular because an image can be sent in little more than half a minute.
Robot 36
Robot 36 is one of the fastest commonly used colour SSTV modes. It is suitable for short transmissions and rapidly changing conditions.
Because less time is available for picture information, the image normally contains less colour detail than a slower high-resolution mode.
Time
Approximately 36 seconds
Resolution
320 × 240
Colour
Reduced colour detail
Best for
Fast transmissions
Robot 72
Robot 72 uses approximately twice the transmission time of Robot 36 and provides improved colour and picture quality.
Time
Approximately 72 seconds
Resolution
320 × 240
Colour
Improved colour detail
Best for
Balanced speed and quality
High-resolution SSTV
PD Modes
PD modes are designed to provide efficient colour transmission and, in several variants, higher image resolution than traditional Martin, Scottie and Robot modes.
The number in the mode name gives an approximate indication of the transmission duration. Longer PD modes normally provide greater detail.
PD50
PD50 provides a relatively fast colour transmission while retaining the characteristic PD colour system.
Time
Approximately 50 seconds
Resolution
320 × 256
Best for
Quick PD contacts
PD90
PD90 offers a useful compromise between transmission duration, picture detail and resistance to changing conditions.
Time
Approximately 90 seconds
Resolution
320 × 256
Best for
General PD operation
PD120
PD120 produces a detailed high-resolution picture in approximately two minutes.
This mode has frequently been used during SSTV events organised through Amateur Radio on the International Space Station.
Time
Approximately 2 minutes
Resolution
640 × 496
Best for
Detailed images and ARISS events
PD180 and Longer Modes
PD180, PD240 and PD290 use longer transmission times to provide detailed pictures.
These modes are most useful when propagation remains stable throughout the complete transmission.
Time
Approximately 3–5 minutes
Resolution
High resolution
Best for
Detailed and stable reception
Choosing a mode
Which SSTV Mode Should You Use?
There is no single best SSTV mode for every situation. The correct choice depends on the radio conditions, available contact time and desired image quality.
Good for Beginners
Martin M1Widely supported, commonly heard and easy to recognise.
Fast Transmission
Robot 36Useful when only a short transmission is required.
General HF Contacts
Martin M1 or Scottie S1Both modes provide a good balance between duration and picture quality.
ISS and ARISS
PD120PD120 has often been used for SSTV transmissions from the International Space Station.
High Resolution
PD120 or LongerSuitable when fine detail is more important than transmission speed.
Changing Conditions
A Shorter ModeA shorter transmission reduces the chance that fading damages a large part of the picture.
Incorrect decoding
What Happens When the Wrong Mode Is Selected?
Selecting the wrong mode can cause a severely distorted picture. The image may have incorrect dimensions, unusual colours, displaced lines or no recognisable content.
Wrong Dimensions
Picture lines may appear too long, too short or positioned in the wrong part of the image.
Incorrect Colours
Colour information can be decoded in the wrong order, producing unrealistic colours.
Slanted Image
Slant is usually caused by tuning or timing differences, although incorrect mode selection can make it worse.
Missing Synchronisation
When the beginning of the transmission is missed, automatic mode detection may fail.
Record the received audio
A recording allows you to decode the transmission again and test another mode when automatic detection was incorrect.
Operating practice
Receiving and Transmitting Modes
Receiving SSTV
Receiving and decoding SSTV signals normally does not require the listener to choose a mode in advance.
Most software detects the VIS code automatically. Manual selection is useful when the start of the transmission was missed.
Transmitting SSTV
Transmitting requires a suitable amateur-radio licence and operation within the regulations and band plan applicable to your country.
Choose a mode appropriate for the frequency, propagation conditions and operators sharing the channel.
Frequently asked questions
SSTV Modes FAQ
Which SSTV mode is most popular?
Martin M1 and Scottie S1 are among the most commonly heard modes on HF. Popularity can vary by region, frequency and operating group.
Which SSTV mode is the fastest?
Several very short modes exist, including monochrome formats. Robot 36 is one of the fastest commonly used colour SSTV modes.
Which mode gives the best picture quality?
Longer high-resolution modes such as PD120, PD180 and longer PD variants can provide excellent detail.
Actual received quality still depends on signal strength, interference, fading, tuning and audio quality.
Which SSTV mode is used by the ISS?
ARISS SSTV events have frequently used PD120. The mode can change, so event information should always be checked before reception begins.
Can software detect the SSTV mode automatically?
Yes. Most SSTV programs use the VIS code at the beginning of the transmission to select the mode automatically.
Why is my received image leaning sideways?
A slanted image is normally caused by a small timing difference, an inaccurate sound-card clock or incorrect receiver tuning.
Many SSTV programs include a slant-correction function.
Does a longer mode always produce a better image?
Not always. A longer mode can provide more detail, but it also gives fading and interference more time to damage the transmission.
During unstable conditions, a shorter mode may produce a more complete picture.
Can I decode a transmission again later?
Yes. Record the received audio as a WAV file or another suitable uncompressed format. The recording can later be played back into SSTV software.
Part of the hobby
Experiment with Different Modes
The best way to learn the differences between SSTV modes is to receive, compare and decode real transmissions.
Listen to several modes and compare their speed, colour quality, resistance to fading and final picture detail.
Over time, the distinctive sound and rhythm of Martin, Scottie, Robot and PD transmissions become easy to recognise.