Slow Scan Television (SSTV) is one of the most fascinating digital modes in amateur radio. Unlike voice contacts or text-based modes such as FT8 and RTTY, SSTV allows operators to exchange actual images over ordinary HF radio channels. The process is surprisingly simple: an image is converted into a series of audio tones, transmitted over the air, and then reconstructed by receiving software at the other end.
One of the first things new SSTV operators notice is the long list of mode options inside programs such as MMSSTV. Buttons labeled Robot 36, Robot 72, Martin 1, Martin 2, Scottie 1, Scottie DX, AVT 90, and SC2-180 often leave beginners wondering which mode they should use. While all SSTV modes accomplish the same basic goal, each was designed with different priorities in mind, balancing transmission speed, image quality, synchronization, and weak-signal performance.
The Most Common SSTV Modes at a Glance
Mode | Transmission Time | Image Quality | Popularity | Best Use Case |
|---|---|---|---|---|
Robot 36 | ~36 seconds | Good | Moderate | Quick image exchanges |
Robot 72 | ~72 seconds | Very Good | Low | Better color reproduction |
Martin 1 | ~114 seconds | Excellent | Very High | General HF SSTV operation |
Martin 2 | ~58 seconds | Good | High | Faster contacts |
Scottie 1 | ~110 seconds | Excellent | Very High | Everyday SSTV use |
Scottie 2 | ~71 seconds | Very Good | Moderate | Faster operation |
Scottie DX | ~269 seconds | Excellent | Moderate | Weak-signal and DX contacts |
AVT 90 | ~90 seconds | Very Good | Low | Experimental operation |
AVT 188 | ~188 seconds | Excellent | Low | High-quality image transmission |
The Origins of SSTV Modes
The original SSTV systems appeared in the late 1950s and transmitted black-and-white images using only 120 scan lines. Over the decades, engineers and experimenters developed improved transmission methods that increased image quality, introduced color, and improved synchronization. Several families of SSTV modes emerged, each becoming popular in different parts of the world.
Mode Family | Origin | Developer |
|---|---|---|
Robot | United States | Robot Research Inc. |
Wraase | Germany | Ulrich Wraase |
Martin | England | Martin Emmerson |
Scottie | Scotland | Eddie Murphy |
AVT | United States | Ben Blish Williams |
Although modern software can automatically switch between these formats, the differences remain important because they affect how well images decode under varying radio conditions.
Robot SSTV Modes
Robot modes were among the earliest color SSTV formats and remain an important part of SSTV history. When I first began experimenting with SSTV, Robot 36 was one of the first modes I encountered because many special event stations continue to use it. The biggest advantage of Robot 36 is speed. A complete color image can be transmitted in approximately 36 seconds, allowing operators to exchange pictures quickly without occupying a frequency for long periods.
Robot 72 takes roughly twice as long but produces noticeably better color reproduction and smoother image transitions. Unlike Martin and Scottie modes, Robot uses luminance and chrominance information rather than transmitting separate red, green, and blue color channels. This was an innovative design when it was introduced and helped establish many of the standards later adopted throughout the SSTV world.
Robot modes also introduced the VIS identification system that automatically tells receiving software which mode is being used. Today, virtually every major SSTV mode uses some form of VIS signaling because it eliminates the need for manual mode selection.
Martin SSTV Modes
If someone asks me which SSTV mode they should start with, my answer is almost always Martin 1. It has become one of the de facto standards for amateur radio SSTV and is supported by every major software package. Martin 1 takes approximately 114 seconds to transmit a full-color image and offers an excellent balance between transmission speed and image quality.
When receiving Martin 1 images on 20 meters, I consistently find them sharp, colorful, and easy to decode. The mode performs well under typical HF conditions and is forgiving enough for beginners who are still learning how to optimize their audio levels and radio settings.
Martin 2 was developed for operators who wanted faster image exchanges. By reducing transmission time to around one minute, it allows more contacts to take place during a busy operating session. While image quality is slightly reduced compared to Martin 1, the difference is often difficult to notice during casual operation.
Scottie SSTV Modes
Scottie modes are every bit as popular as Martin modes and have developed a loyal following among SSTV enthusiasts. Scottie 1 is often considered the direct competitor to Martin 1 because both produce high-quality images and require roughly the same transmission time.
During normal band conditions, I find Scottie 1 and Martin 1 produce remarkably similar results. The choice frequently comes down to operator preference or local convention. Some SSTV nets favor one mode over the other, but both remain widely accepted throughout the amateur radio community.
Scottie 2 shortens transmission time while maintaining good image quality, making it useful when conditions are changing rapidly. The most interesting member of the Scottie family, however, is Scottie DX. This mode was specifically designed for weak-signal operation and long-distance contacts. By transmitting much more slowly, Scottie DX allows receiving software to extract image information from signals that would otherwise be unreadable.
Feature | Martin 1 | Martin 2 | Scottie 1 | Scottie 2 | Scottie DX |
|---|---|---|---|---|---|
Speed | Slow | Medium | Slow | Medium | Very Slow |
Image Detail | Excellent | Good | Excellent | Very Good | Excellent |
Weak Signal Performance | Good | Fair | Good | Good | Excellent |
Common on HF Bands | Very Common | Common | Very Common | Common | Occasional |
Recommended for Beginners | Yes | Yes | Yes | Yes | No |
For operators interested in DX contacts or marginal propagation conditions, Scottie DX remains one of the most effective SSTV modes available.
AVT Modes
AVT stands for Amateur Television and differs significantly from Robot, Martin, and Scottie formats. Rather than relying on traditional horizontal synchronization pulses, AVT uses highly accurate timing and digital synchronization techniques. This makes the mode exceptionally efficient but also places greater demands on timing accuracy.
AVT 90 and AVT 188 are the two most commonly encountered versions. AVT 90 offers a good compromise between speed and image quality, while AVT 188 focuses on maximizing detail. Although AVT modes are less common on the HF bands today, they continue to attract operators who enjoy experimenting with alternative SSTV technologies.
The design philosophy behind AVT was to improve synchronization reliability while reducing overhead. It remains one of the most technically interesting SSTV families ever developed.
High-Resolution SSTV Modes
As computer technology advanced, several high-resolution SSTV formats emerged. Modes such as SC2-180 and Scottie DX focus on maximizing image quality rather than minimizing transmission time. These formats can take several minutes to complete a single image, but the resulting pictures often contain significantly more detail than traditional SSTV transmissions.
I find these modes particularly interesting during demonstrations and special event operations because they showcase just how much information can be transmitted through a standard SSB radio channel. While they are not ideal for casual contacts, they demonstrate the impressive capabilities of analog image transmission over HF radio.
Speed Versus Quality
Every SSTV operator eventually discovers that image quality and transmission speed are closely related. Faster modes allow more contacts but sacrifice some detail. Slower modes require patience but reward operators with superior image quality and improved weak-signal performance.
Mode | Speed Rating | Quality Rating |
|---|---|---|
Robot 36 | 5/5 | 3/5 |
Martin 2 | 4/5 | 4/5 |
Scottie 2 | 4/5 | 4/5 |
Robot 72 | 3/5 | 4/5 |
Martin 1 | 2/5 | 5/5 |
Scottie 1 | 2/5 | 5/5 |
AVT 188 | 1/5 | 5/5 |
Scottie DX | 1/5 | 5/5 |
Which SSTV Mode Should You Use?
For most amateur radio operators, Martin 1 remains the safest and most practical choice. It is widely supported, commonly used on the HF bands, and produces excellent results. Scottie 1 is an equally strong option and is often preferred by experienced SSTV operators who have used the mode for years.
If speed is your primary concern, Robot 36 and Martin 2 can significantly reduce transmission time. If you regularly operate under poor band conditions or enjoy chasing DX stations, Scottie DX is difficult to beat. Operators interested in experimentation may find AVT modes particularly rewarding.
If You Want To… | Recommended Mode |
|---|---|
Send images as quickly as possible | Robot 36 |
Use the most popular SSTV format | Martin 1 |
Work weak DX stations | Scottie DX |
Get maximum image quality | Martin 1 or AVT 188 |
Experiment with alternative modes | AVT 90 |
Reduce transmission time during contests | Martin 2 |
Improve decode reliability over long paths | Scottie DX |
Exchange casual images with other operators | Martin 1 or Scottie 1 |
The best SSTV mode ultimately depends on your operating style, propagation conditions, and personal preferences. Understanding the strengths and weaknesses of each format will help you choose the right tool for every contact and make your SSTV experience far more enjoyable.
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