What Is SSTV?

SSTV is basically the transmitting of "still" photos to multiple recipients simultaneously over radio. Using radio as the medium you can successfully send a photo from your computer to one or more people at the same time. This, you may think is what FAX is all about. These pictures can be black and white, grey scale, or color OR any combination of those in one.

In the explanation below I will describe the modulation of this digital mode. SSTV is generally transmitted in the voice sub-bands and in HF, it is usually sent using SSB. You can transmit this mode using FM or any other modulation - such as on a 2 meter frequency on FM or even thru a repeater.

Specification

VIS Code and Robot calibration header

All standard SSTV modes utilize a unique digital code that identifies the mode to a receiving system. The code is called the VIS, or Vertical Interval Signal code. Although the entire calibration header is often referred to as the VIS Code, the code itself is only a part of it. The seven-bit code is transmitted least-significant bit (LSB) first, and uses even parity.

Calibration header with VIS code

TIME(ms)FREQUENCY(hz)IDENTITY
3001900Leader tone
101200break
3001900Leader tone
301200VIS start bit
30bit 01100hz = 1, 1300hz = 0
30 bit 1 1100hz = 1, 1300hz = 0
30 bit 2 1100hz = 1, 1300hz = 0
30 bit 3 1100hz = 1, 1300hz = 0
30 bit 4 1100hz = 1, 1300hz = 0
30 bit 5 1100hz = 1, 1300hz = 0
30 bit 6 1100hz = 1, 1300hz = 0
30 PARITY Even=1300hz, Odd=1100hz
30 1200 VIS stop bit

SCOTTIE MODES

Scottie modes, although the most commonly used modes in the US, are unusual for two reasons. The combination of the two has caused considerable confusion over the years:

  • The first scan line (only) begins with an out-of-sequence 9.0ms starting sync pulse, at 1200hz.
  • The regular sync pulse is positioned between the Blue and Red scans, rather than at the line break, as with other modes.

VIS CODES Scottie 1 60d (decimal)
Scottie 2 56d
Scottie DX 76d

COLOR MODE = RGB (1500-2300hz luminance range)
SCAN SEQUENCE = Green, Blue, Red
NUMBER OF LINES = 256
NORMAL DISPLAY RES 320x256 (including 16-line header)

TRANSMISSION TIME
Scottie 1 = 109.6 seconds (not including cal. header/VIS)
Scottie 2 = 71.1 seconds
Scottie DX = 268.9 seconds

COLOR SCAN TIME
Scottie 1 138.240ms (.4320ms/pixel @ 320 pixels/line)
Scottie 2 88.064ms (.2752ms/pixel @ 320 pixels/line)
Scottie DX 345.6ms (1.0800ms/pixel @ 320 pixels/line)

TIMING SEQUENCE
(1) Starting sync pulse (first line only!) 9.0ms 1200hz
(2) Separator pulse 1.5ms 1500hz
(3) Green scan
(4) Separator pulse 1.5ms 1500hz
(5) Blue scan
(6) Sync pulse 9.0ms 1200hz
(7) Sync porch 1.5ms 1500hz
(8) Red scan
 
After the first line, repeat steps 2 thru 8 for all following lines.

Listen to SSTV

SSTV has a very distinct sound which is easy to identify if you get a grasp for what it's basics are. The explanation I presented on the left side is for one single mode of SSTV, Scotty. There are several and various modes available for SSTV operation. Some are faster than others and some are only black and white, such as the older robot modes, which are both very fast and Black and White. This is a low resolution mode from the old days, but some are still sending in it on occasion. The most common modes are Scotty and Martin, however. Below are clickable links which will play the various modes so you can learn to identify them. There will be a test at the end of this chapter..... Just kidding!

  • Scotty 1
  • Scotty 2
  • Scotty DX
  • Martin 1
  • Martin 2
  • Robot 36
  • Robot 72
  • AVT 90

    • Remember, looking at the description to the left, you'll see that the VIS code is sent in each line of the picture. This is what many of the SSTV programs, including MMSSTV uses to auto-sync and auto-lock onto the proper mode even if you didn't receive the beginning of the picture file. For details on using MMSSTV, please refer to the author's website, there is too much to get into on this page. Just know that in most cases it just works out of the box.

    One last thing to note, you should calibrate your sound card to operate on the standard frequency. This is done very easily using MMSSTV and WWV. WWV's click tone is used by MMSSTV to calibrate the software and sound card. When you have a properly setup system, there will be no "skew" to the picture and everyone will see a straight picture if you send one. This is important to do to prevent people from complaining that your pictures are skewed.

    Common Frequency

    The most common frequency to find SSTV on would have to be 14.230Mhz. This is pretty busy all the time, especially during the daytime. There are others which are considered "common" frequencies for SSTV, but this one is by far the most popular HF frequency. Sit there for a short time and you're sure to find someone sending a random picture. Although 7.130Mhz is common for DSSTV, they do occasionally send SSTV on there as well. Check them both out for SSTV pictures.

    Software Download

    Here is a link to download MMSSTV for yourself.
    MMSSTV Download Link
    After installing, visit their website at MMSSTV page for more information and to download sample files and so on.

    Hope to "see" you on 20 meters some day! Create that unforgettable QSL card and send it to the world! Many people show off their prized pets and even their kids on the radio. Join in on the fun. Check out the other digital modes here on my website too!