MMSSTV HELP · CHAPTER 03

Transmitting SSTV

Preparing an image, selecting a mode and transmitting Slow Scan Television with MMSSTV.

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The TX window

To transmit an SSTV picture, open the TX tab in the MMSSTV main window. The picture displayed in the TX window is the picture that MMSSTV will transmit — What You See is What You Transmit.

DO NOT USE THE SPEECH PROCESSOR FOR SSTV.

Set the transmitter audio or microphone gain carefully. SSTV uses precise audio tones and excessive processing or overdrive can distort those tones.

Preparing the TX image

The original documentation describes several ways to prepare the TX image:

  1. Drag an image from the stocked picture gallery into the TX window.
  2. Drag an image from the MMSSTV folder thumbnail window.
  3. Drag an image from Windows Explorer into the TX window.
  4. Drag an image from another image program that supports drag-and-drop.
  5. Copy and paste an image through the Windows clipboard.

A template can be superimposed over the TX picture to add callsigns, reports, contest numbers, text, colour bars and other information.

Selecting the SSTV mode

Select the mode you want to use before starting transmission.

If SSTV mode fixed is unchecked in the TX page of the MMSSTV Setup options, MMSSTV can automatically use the mode of the most recently received SSTV picture.

Starting the transmission

  1. Prepare the picture in the TX window.
  2. Select the desired SSTV mode.
  3. Check the transmitter audio level.
  4. Press the TX button.

During transmission, a horizontal marker moves down the image as each section is sent. MMSSTV automatically returns to RX when the transmission is complete. To abort, press the TX button again.

TX sound buffer

MMSSTV uses a 12-second sound buffer during transmission. The original documentation notes that on slower computers it is better not to perform other demanding operations while an image is being transmitted.

If MMSSTV reports lost TX timing, increasing the FIFO setting in the Misc section of Setup may help.

TX slant adjustment

Some sound cards use slightly different clock rates for recording and playback. An RX picture can therefore be correctly adjusted while the transmitted picture still appears slanted at the receiving station.

MMSSTV provides separate sound-card clock adjustment for RX and TX.

Tune and CWID

MMSSTV includes a tone generator associated with the Tune button. The original documentation describes a 1750 Hz tone for repeater use.

MMSSTV can also transmit a CW identification after an SSTV transmission when CWID is enabled in the TX setup.

This chapter is based on the original MMSSTV Basic Operations documentation by Makoto Mori, JE3HHT, translated into English by JA7UDE Nobuyuki Oba.
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