SSTV

SSTV stands for Slow Scan TeleVision. It is a mode used by amateur radio operators to send images, both color and black and white. An SSTV image takes from 8 seconds to several minutes to receive, depending on the mode used. In North America, Scottie S1 is the most commonly used mode. In Europe, Martin M1 is the most commonly used mode.

In the top button, the current SSTV mode is displayed. Clicking on the mode will display a popup menu, from which a new mode will be selected. MultiMode will automatically select the mode based on the VIS code sent. However, it is possble for the VIS code to get garbled, or you may manually start reception. Under these conditions, you need to select the correct SSTV mode. You may do so even while receiving an image, the old data ia preserved, and the image display will be automatically adjusted and updated.

 

This button will clear the SSTV display, and reset the mode. MultiMode will now wait for the start signal and VIS code of the next SSTV image.

 

These two buttons are used to shift the image to the left and right. This is useful when reception was manually started. Holding down the option key while clicking will move the picture further each time. Holding down shift will cause it to jump even further, and is useful for making gross adjustments.

 

The + and - buttons are used to adjust for timing differences between your Mac and the computer sending the SSTV image. Small offsets in timing can cause large skewing of the image. If the vertical edges of the image are diagonal, then these buttons should be used to correct the timing. The timing variation is shown to the right of the three buttons. 1.00000 means the timing is at the default value. 

Clicking the + or - button will change the timing by 0.00001. Holding down the control key while clicking will cause the timing to change by 0.00010. Holding down the option key will cause the timing to change by 0.00100. The No Slant button will reset the timing to the default value. You can change the timing while receiving an image, and the display will be automatically updated in real-time. 

 

The Start Reception button allows you to manually start receiving an SSTV image. This is useful if the start signal and/or VIS code are not correctly received. It is also useful if you tune into a transmission that is already in progress.

The Stop Reception button will stop reception of an image. Normally this occurs after the receive buffer fills up, after about four minutes.

 

The Save Picture button allows you to quickly save a received SSTV picture. The picture is saved to the folder selected in the SSTV section of the preferences, with a filename consisting of the date and time the image was stored.

SSTV Transmission

There may be some slight timing offsets in some of the modes, please bear with them for now.

To transmit an SSTV image, perform the following steps:

1. Select SSTV Mode.
2. Select the SSTV mode you wish to use.
3. Push the Picture From File... button located on the right side of the SSTV image
     display area.
4. A file open dialog will appear. Select the picture file. Note: at present, it must be
    a PICT file. The should be the same size as the transmission mode uses, or some 
    distortion may occur as the image is scaled. 
5. A preview of the image to send is shown. Click on OK to proceed, or Cancel to abort.
6. After the sound output file is built (when the watch cursor reverts to a normal
    cursor) you may select Transmit mode from the Control menu, and the picture
    will be sent.  During transmission, the DTR line of the selected serial port will be
    active (if a port was selected), this may be used as a PTT signal to a transmitter. 

It is best to not try to do too much else with your Mac while transmitting an SSTV image, or the audio may start to skip, especially on slower machines.

At present, a 16 line grayscale title is included in all modes. You can enter your callsign into this title by going to the General Preferences, and entering it into the Call field. If your copy of MultiMode is unregistered, then UNREG will be sent as your callsign.

If you have a QuickTime compatible camera connected to your system, you can push the
Capture Image button to capture an image to send. When you push the button, you'll get a small window with real-time video from your camera. Click the Capture button, and the image will be captured and made ready to send. The Capture Settings... button can be used to configure your camera.

SSTV Modes

MultiMode supports the following SSTV modes. Is your favorite mode not listed? Email me with the specifications for the mode, and I'll add support for it! 

Robot Modes
8 Second B&W
12 Second B&W
24 Second B&W
36 Second B&W
36 Second Color 
72 Second Color 

Martin Modes
Martin M1
Martin M2
Martin M3
Martin M4

Scottie Modes
Scottie S1
Scottie S2
Scottie S3
Scottie S4
Scottie DX

SSTV Frequencies

The following SSTV frequencies are commonly used. 14230 MHz is by far the most popular frequency. SSTV nets may be heard throughout the weekend.

  3720 kHz LSB
  3730 kHz LSB
  7033 kHz LSB
14230 kHz USB
18160 kHz USB
21340 kHz USB
28680 kHz USB
28700 kHz USB
50300 kHz USB

144.500 MHz FM
144.525 MHz FM
145.985 MHz FM (MIR space station on weekends)
433.700 MHz FM
433.925 MHz FM