Slow-scan television
Slow-scan television (SSTV) refers to any method of sending still pictures over amateur radio. Although the vast majority of SSTV activity today uses computers for modulation and demodulation (similar to many digital modes), most SSTV modes are technically analog.
A more general term for technologies including SSTV is narrowband television (NBTV). 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 transmission than broadcast television, usually taking from about eight seconds to a couple of minutes, depending on the mode used, to transmit one image frame. Because of this, it is used for still images, not video. (Other NBTV systems, which are less commonly used, transmit video, but at very low resolution.)
Since SSTV systems operate on voice frequencies, they can be used with most amateur transceivers, including on HF, VHF and UHF.
Most SSTV operators today use a personal computer and special software in place of much of the custom equipment formerly necessary. The sound card of a PC, with special processing software, acts as a modem. The computer screen provides the output. A digital camera or saved digital photos provide the input. More recently, it is possible to use an Android or iOS smartphone or tablet for SSTV. This can be very convenient, because the camera is integrated into the device and can be easily moved and pointed. This could be especially useful for emergency communications; it is possible to send an image over several miles in only two or three minutes using nothing more than a smartphone and an HT.
For best image quality, a radio-computer interface such as a SignaLink can be used. However, the "air link" method of holding the radio's microphone near the computer's speaker and vice versa can also be used, at the expense of image quality. A useful image-receiving technique is to record the audio, perhaps with a smartphone, and then demodulate the image from the recording.
Software
Android
On Android, the transmit and receive functions are provided by separate apps. The encoder, simply called "SSTV Encoder," is available on the Google Play Store and on F-Droid. (If you're not sure which link to use, use the Play Store.) The decoder is called "Robot36"; despite the name, it supports many different modes. It is also available from the Play Store and from F-Droid.
Air link works fine with Android devices, and it is much more convenient than with a laptop or (especially) a desktop. However, with a "USB On-The-Go" adapter, many phones and tablets will work with the SignaLink.
Sending pictures
To send a picture, use the "SSTV Encoder" app.
First, tap the three-dot menu, then tap "Modes" and select a mode. PD90 is a good compromise between image quality and transmission time; it takes 90 seconds.
Tap the photo frame button and select an image. (The camera button should allow pictures to be taken from within the app, but this feature is buggy. It is better to take a picture with the normal camera app first.) Zoom and drag the picture as desired; the part within the frame will be transmitted.
Tap anywhere within the frame to add text at that location; an editor will open in which you can enter text and change the font size, style, and color. Click the check mark when you are done. If you want to edit text that is already on the image; tap the text, and the editor will open with that text pre-loaded. When you click the checkmark, it will save the edit. To remove text, simply edit it and remove all of the text; you can use the X icon to do this.
To send the image, turn your media volume up and tap the "play" icon.
iOS and iPadOS
An SSTV decoder/encoder app is available for the iPhone and iPad, current price is $2.99. This works in a pinch, though computer-based apps such as QSSTV do a better job demodulating the image.
Windows
MMSSTV is an SSTV modem for Windows. It has not been updated since 2010, but it still works fine.
Linux
QSSTV is an SSTV program for Linux. If you are familiar with the process for compiling and installing programs from source code, follow the instructions on the GitHub repository. Otherwise, search for "QSSTV" in your distribution's software manager.
MacOS
MultiScan3B by KD6CJI is available as a free download. The European Space Agency has a video tutorial installation and use.
MultiMode Cocoa apparently supports several SSTV modes along with some digital modes such as PSK31, but it costs $89 and it is not know how well it works, putting it in a similar situation as the iOS app.
In principle QSSTV could be ported to MacOS, though nobody has yet stepped forward to do so.
External links
ARISS SSTV Archive
Slow scan TV net
Copyright
Copyright © 2002-2022 Wikipedia contributors. See the edit history of "Slow-scan television" on Wikipedia up to and including 11 March 2022.
Copyright © 2022-2023 Pelican Bay Amateur Radio Club Wiki contributors. See the edit history of "Slow-scan television" on the PBARC Wiki up to and including 7 March 2022.