Slow Scan Television (SSTV)


From Wikipedia, Slow Scan television (SSTV) is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color. SSTV transmissions often appear like QSL Cards but as an image with station call signs, RST reception reports, and other information typically found on a QSL card.


A literal term for SSTV is narrowband television. Analog broadcast television requires at least 6 MHz wide channels, because it transmits 25 or 30 picture frames per second, but SSTV usually only takes up to a maximum of 3 kHz of bandwidth. It is a much slower method of still picture transmission, usually taking from about eight seconds to a couple of minutes, depending on the mode used, to transmit one image frame.


Since SSTV systems operate on voice frequencies, amateurs use it on HF, VHF and UHF radio.




The concept of SSTV was introduced by Copthorne Macdonald in 1957–58. He developed the first SSTV system using an electrostatic monitor and a vidicon tube. In those days it seemed sufficient to use 120 lines and about 120 pixels per line to transmit a black-and-white still picture within a 3 kHz phone channel. First live tests were performed on the 11 Meter ham band – which was later given to the CB service in the US. In the 1970s, two forms of paper printout receivers were invented by hams for printing your SSTV images as they were received.


The first space television system was called Seliger-Tral-D and was used aboard the Soviet Vostok. Vostok was based on an earlier videophone project which used two cameras, with persistent LI-23 iconoscope tubes. Its output was 10 frames per second at 100 lines per frame video signal.


The Seliger system was tested during the 1960 launches of the Vostok capsule, including Sputnik 5, containing the space dogs Belka and Strelka.


Vostok 2 later an improved 400-line television system referred known as Topaz which was a second-generation system incorporating docking views, overlay of docking data and was introduced after 1975.


SSTV was first used to transmit images of the far side of the Moon from the early Luna 3 mission. Americans used SSTV on Faith 7 in the early years of the NASA Apollo program.


The Faith 7 camera transmitted one frame every two seconds, with a resolution of 320 lines.


The Apollo TV cameras used SSTV to transmit images from inside Apollo 7, Apollo 8, and Apollo 9, as well as the Apollo 11 Lunar Module television from the Moon.


NASA unfortunately had taken all the original tapes and erased them for use on subsequent missions. Later on the Apollo 11 Tape Search and Restoration Team formed in 2003 tracked down the highest quality footage among the converted recordings of the first broadcast, pieced together the best footage, then contracted a specialist film restoration company to enhance the degraded black-and-white film and convert it into digital format for archival records.


The SSTV system used in NASA's early Apollo missions transferred ten frames per second with a resolution of 320 frame lines using less bandwidth than a normal TV transmission.


Due to their in-house advancements the SSTV systems used by NASA now differ significantly from the SSTV systems currently in use by amateur radio enthusiasts today.


The Original Ham Radio SSTV Systems


SSTV systems started appearing in the United States in 1970, after the FCC had legalized the use of SSTV for advanced level amateur radio operators in 1968.


Amateur SSTV originally required quite a bit of specialized equipment. Usually there was a scanner or camera, a modem to create and receive the characteristic audio howl, and a cathode ray tube from a surplus radar set. The special cathode ray tube would have "long persistence" phosphors that would keep a picture visible for the about ten seconds.


The modem would generate audio tones between 1200 and 2300 Hz from picture signals, and picture signals from received audio tones. The audio would be attached to a radio receiver and transmitter.


Current SSTV Systems


A modern system, having gained ground since the early 1990s, uses a personal computer and special software in place of much of the custom equipment from the 70’s. The radio sound card, your computer, and special processing software acts as a modem. The computer screen provides the output. A small digital camera or digital photos provides the input.




Like the similar radio fax mode, SSTV is an analog signal. SSTV uses frequency modulation, in which every different value of brightness in the image gets a different audio frequency. In other words, the signal frequency shifts up or down to designate brighter or darker pixels, respectively. Color is achieved by sending the brightness of each color component (usually red, green and blue) separately. This signal can be fed into an SSB transmitter, which in part modulates the carrier signal.


There are a number of different modes of transmission, but the most common ones are Martin M1 (popular in Europe) and Scottie S1 (used mostly in the USA). Using one of these modes, an image transfer takes just under two minutes. Some black and white modes take only 8 seconds to transfer an image.




A calibration header is sent before the image. It consists of a 300-millisecond leader tone at 1900 Hz, a 10 ms break at 1200 Hz, another 300-millisecond leader tone at 1900 Hz, followed by a digital VIS (vertical interval signaling) code, identifying the transmission mode used. The VIS consists of bits of 30 milliseconds in length. The code starts with a start bit at 1200 Hz, followed by 7 data bits (LSB first; 1100 Hz for 1, 1300 Hz for 0). An even parity bit follows, then a stop bit at 1200 Hz.




Because there are multiple modes available, they behave in different ways when sending the image data. A transmission consists of horizontal lines, scanned from left to right. The color components are sent separately one line after another. The color encoding and order of transmission can vary between modes. Most modes use an RGB color model; some modes are black-and-white, with only one channel being sent; other modes use a YC color model, which consists of luminance (Y) and chrominance (R–Y and B–Y). The modulating frequency changes between 1500 and 2300 Hz, corresponding to the intensity (brightness) of the color component. The modulation is analog, so even though the horizontal resolution is often defined as 256 or 320 pixels, they can be sampled using any rate. New SSTV images have resolutions of 640 x 496 and the image aspect ratio is conventionally 4:3. Lines usually end in a 1200 Hz horizontal synchronization pulse of 5 milliseconds (after all color components of the line have been sent); in some modes, the synchronization pulse lies in the middle of the line.




There are many SSTV modes and their differences are numerous. These modes share many properties, such as synchronization and/or frequencies and grey/color level correspondence. But their main difference is the image quality, which is proportional to the time taken to transfer the image. Modern SSTV software can be set to operate in Automatic mode where the software detects and changes the mode to match the incoming image. This is a big convenience for the operator.




Using an HF radio capable of demodulating single-sideband modulation, SSTV transmissions can be heard on the following frequencies in the HF Band:





80 meters

3845 kHz (3730 in Europe)


40 meters

7170 kHz (7165 in Europe)


20 meters

14,230 kHz


15 meters

21,340 kHz


10 meters

28,680 kHz



So How Do Ham’s Typically Use SSTV?


Traditionally SSTV is used on the HF bands by exchanging SSTV images in place of the back and forth QSO that we’re familiar with on CW or Phone modes.


Just like modern digital modes Amateur enthusiasts of SSTV will set up their shack with a transceiver, radio soundcard, computer and SSTV software. In the software is a SSTV image editor that allows for text to be added over top of the background image that you plan to broadcast. The image can be your ham shack, your antennas, a nice scenery image of the area where you live, anything that’s in good taste and it not offensive.


All the common information shared in a QSO like your callsign and signal reports are delivered as text over the image in the broadcast. Multiple images being broadcast back and forth with different text being shared is required to complete the average QSO.


Again, like any exchange you start by broadcasting your image with CQ and your Callsign. After each transmission give a fairly decent break to allow anyone replying time to start transmitting back. If nothing is heard, then you can broadcast your CQ again.


When another amateur does receive your CQ image they will transmit back their SSTV image and start the exchange. For timely exchanges make sure that you acknowledge their image, respond with their callsign for verification, and add a signal report.


Like any HF QSO, the exchange may be done in just a few transmissions, or you may continue to pass images back and forth asking questions or sharing additional information.


The exchange is over when you both are competed and have all the required information to log a contact.


SSTV from Space


Over two weeks this past month, the crew on the International Space Station was broadcasting SSTV images for terrestrial amateurs to try and receive. Unlike traditional HF SSTV these broadcasts were done over VHF, and the challenge was receiving the images during the short 5-6 minute Passovers that the ISS might make over your location only a few times in any given day. These passes if directly overhead might have a strong signal, but if they are lower or higher on the horizon, the signal might be weak.


Here is a summarized version of the press release from the event.


ARISS is planning another of their popular Slow Scan Television (SSTV) experiment events.


International Space Station (ISS) transmissions are scheduled to begin Friday, Feb. 8 at 14:00 UTC and run through Sunday, Feb. 10 at 18:30 UTC on 145.800 MHz FM with the SSTV mode PD120.


Update Feb. 9: SSTV transmissions on Friday were at very low power, however full power was restored on Saturday afternoon.


ARISS Slow Scan TV (SSTV) operations is a process by which images are sent from the International Space Station (ISS) via ham radio and received by ham operators, shortwave listeners and other radio enthusiasts on Earth, similar to pictures shared on cell phones using twitter or Instagram.


When this event becomes active, SSTV images will be transmitted from the ISS on the frequency of 145.800 MHz using the SSTV mode of PD120.


They can be received using ham radio equipment as simple as a 2-meter handheld radio or a common shortwave or scanner receiver that covers the 2 meter ham band.


After connecting the audio output of the radio receiver to the audio input of a computer running free software such as MMSSTV, the SSTV images can be displayed.


Transmissions will consist of eight NASA On The Air (NOTA) images. In additional, four ARISS commemorative images will also be included for a full set of 12 images.


Once received, Images can be posted and viewed by the public at our website. You can receive a special SSTV ARISS Award for posting your image. Once the event begins, see details at our website.


Please note that the event is dependent on other activities, schedules and crew responsibilities on the ISS and are subject to change at any time.


NORAC member Lorne VE7LWK was ready to listen for the images on the first weekend and got a few of them even with the low power programs being experienced on the ISS radio equipment. He submitted them to the NORAC website and they’re up there for you to see and enjoy.


When the second weekend was announced I decided to give it a try and here’s a summary of how I did it.


I started with my ultra-cheap USB RTL-SDR receiver hoping to do all the work digitally in my PC. I was using my super discone antenna and didn’t get strong enough signals coming in to be able to decode anything that well.


After a few pass overs of the ISS Friday this receiver and antenna combination was not doing the trick so Saturday morning I switched to the following setup.


  • My Yaesu FT-847 all-band, all-mode satellite transceiver
  • A RigBlaster Advantage (soundcard)
  • A Comet GP-3 dual band VHF/UHF vertical antenna up about 40 feet on my little tower.
  • The Ham Radio Deluxe software specifically the Satellite Tracking application.
  • And the MMSSTV software


The configuration was relatively simple to setup.

  • The radio was connected to the antenna and tuned to the VHF frequency of the ISS downlink radio.
  • The audio from the radio was wired into the RigBlaster soundcard.
  • The output of the RigBlaster was a single USB connection into the PC carrying the CAT rig control connection as well as the audio from the radio.
  • The Ham Radio Deluxe software was controlling the radio and the Satellite Tracking module of HRD was tracking the ISS and showing me when the next Passovers would occur and how strong they would be. A nice bonus feature of HRD was the ISS downlink frequency was undergoing tiny automatic changes to accommodate for the Doppler effect of the signal coming from the ISS in earth’s orbit.
  • The final and core piece of technology was a software program call MMSSTV. This free software was configured to listen to the incoming audio from the radio soundcard and automatically decode any images as their broadcasts were detected.
  • Setting up MMSSTV was really easy and there were some handy videos on YouTube from other amateurs talking about their configurations and what settings were important.


From Saturday morning till the event was over Sunday morning I left all the equipment running and received images from 5-6 pass overs in that roughly 24-hour period.


The images I received numbered about 10-11 and varied in quality from good to bad but readable.           


Going online after the weekend there were many amateurs around the world receiving these images. Some of them using the most basic is systems that consisted of a handheld vhf radio with the built in rubber ducky antenna and an app on their cell phone decode the audio stream. The audio was not even wired from one device to the other, the person was just holding both close to each other and letting the noise transmit from speaker on one to the microphone on the other. Even something this basic worked well enough to receive some blurry images.