SSTV — Slow Scan Television
Slow Scan Television (SSTV) is a method of transmitting and receiving still images over radio. Unlike fast-scan broadcast television, SSTV takes several seconds to minutes to transmit a single image, encoding it as audio tones transmitted over an SSB radio. The result is a colour or greyscale image received by another station's software and displayed on screen. SSTV has been an amateur radio tradition since the 1950s, and remains active today — particularly on 14.230 MHz (20m) where images are exchanged regularly, including occasional transmissions from the International Space Station.
Image encoding
SSTV converts image pixel colours into audio tones that are transmitted over SSB radio. Each horizontal line of the image is scanned left to right, with each pixel encoded as an audio frequency — typically 1500 Hz for black and 2300 Hz for white, with shades in between. A sync pulse at the start of each line allows the receiving software to reconstruct the image correctly. Colour SSTV modes use multiple passes to transmit the red, green, and blue components of each line. The entire process takes from a few seconds (Robot 8) to several minutes (Scottie DX), depending on the mode and resolution.
Common SSTV modes
There are many SSTV modes, each offering different trade-offs between transmission time, resolution, and colour fidelity. Martin M1 is the most widely used mode on HF, transmitting a 256x256 colour image in about 114 seconds. Scottie S1 is also popular. Robot 36 and Robot 72 are faster modes with lower resolution. PD-120 and PD-180 offer higher resolution for better image quality when band conditions permit longer transmissions. Your SSTV software will decode any mode automatically by detecting the characteristic sync pulse and mode identifier embedded in each transmission.
Get SSTV software
MMSSTV is the most popular Windows SSTV program — free, well-maintained, and supports all common modes. Download from hamsoft.ca or search for MMSSTV. For Mac users, MultiScan 3B is a paid option. Fldigi also supports basic SSTV. On Android, Robot36 is an excellent mobile SSTV decoder that works even with the phone's microphone held near a radio speaker.
Connect your radio
SSTV uses the same sound card interface connection as other digital modes. Connect your radio's audio output to your computer's sound card input. For transmitting, connect the computer audio output to your radio's microphone or audio input through the interface. Set your radio to USB mode. For receiving only, you can simply connect a cable from your radio's speaker output to your computer's line input — no PTT switching is required for receive-only monitoring.
Tune to an SSTV frequency
Tune your radio to 14.230 MHz USB and watch the MMSSTV waterfall. SSTV transmissions appear as wide slanted bands sweeping across the waterfall as each line of the image is transmitted. MMSSTV will automatically detect the mode and start displaying the incoming image line by line in real time. The ISS occasionally transmits SSTV during special events — check ARISS (Amateur Radio on the International Space Station) announcements for schedules.
Transmit your first SSTV image
In MMSSTV, load an image into the transmit buffer — a photograph, a simple graphic, or a template with your callsign. Select Martin M1 mode. Make sure the frequency is clear (SSTV transmissions are long — be sure no one is using the frequency). Key up and click transmit — MMSSTV will generate the SSTV audio tones and transmit the image. The software controls PTT automatically through your interface.
| Band | Frequency | Notes |
|---|---|---|
| 20m | 14.230 MHz USB | Most active SSTV frequency worldwide |
| 40m | 7.171 MHz USB | Regional SSTV activity |
| 80m | 3.730 MHz USB | Regional, mostly evenings |
| 15m | 21.340 MHz USB | When band is open — good DX |
| 2m | 144.500 MHz FM | Local VHF SSTV, less common |
| ISS | 145.800 MHz FM | Special events only — check ARISS announcements |
How do I receive SSTV from the International Space Station?
When the ISS transmits SSTV (typically during special events or educational outreach), it uses 145.800 MHz FM. You need a VHF receiver or a dual-band radio that covers 2m, a simple vertical or yagi antenna, and SSTV decoding software. The ISS passes over most locations multiple times daily. ARISS (amsat.org/ariss) posts announcements when SSTV transmissions are scheduled. The passes last only about 10 minutes, so timing and a clear horizon to the south are important.
What image should I transmit on SSTV?
Most operators transmit an image that identifies their station — a photo of their shack, antenna, or location with their callsign overlaid. MMSSTV includes template editor that lets you add callsign text and other information to images. Keep the image content appropriate for amateur radio — standard Part 97 content rules apply. Many operators collect received SSTV images and post galleries online.
Why does my received SSTV image have diagonal lines or be skewed?
Diagonal lines in a received image typically indicate a slight timing mismatch between the transmitting and receiving stations — the SSTV software's clock is slightly off from the transmitted signal. MMSSTV has a manual calibration function to adjust the slant. A skewed image (leaning left or right) usually means the receive level is too high or too low — adjust the audio input level until the image straightens.
Can I use SSTV on VHF/UHF FM?
Yes — SSTV works on FM as well as SSB, though the audio frequency response of FM radios can affect image quality. On VHF/UHF, SSTV is less common than on HF but is used occasionally for local image exchange. 144.500 MHz is the standard 2m SSTV calling frequency in many regions. The setup is the same as HF SSTV but using FM mode and a VHF/UHF radio.