John Wells, M5AML. QTH: Derby, IO92GW.

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The software I use is the highly popular MMSTV by Mako Mori.  The software is free and runs in Windows, using the PC soundcard for SSTV input and output.  The software supports all the common SSTV modes such as Martin, Scottie, and Robot.  MMSSTV also includes more specialised systems such as high definition, and experimental narrow bandwidth modes.

The image below is an example of four SSTV pictures I received during a QSO with YO2MFZ

SSTV QSO pictures

Each picture is 320 x 256 pixels - not high quality but a good trade-off between picture resolution and transmission time

As mentioned above, higher resolution SSTV modes are supported by MMSSTV but they are rarely used.  Traditionally Martin 1 and Martin 2 modes are usually used by European stations and Scottie 1 and Scottie 2 are used by North American and Asian stations.  It doesn't really matter which you use as long as you use the same mode as the other station(s) in your QSO - this is basic SSTV etiquette.

In multipath conditions Martin and Scottie modes do not perform well so it is better to use the MP or SC2 modes on 80m at night. SC2 120 and SC2 180 are the most popular multipath tolerant modes.

The images below were received on 80m within a few minutes of each other over the same path.  Ignoring the noisy lines - probably due to QSB - it can be seen that the SC2 180 image has good vertical synchronisation and no herringbone pattern unlike the Scottie 2 image.

SC2 180 Scottie 2

Due to the small size of the WARC bands (30m, 17m and 12m) narrow bandwidth SSTV (N-SSTV) is recommended for use on those bands.

Common SSTV frequencies in Europe are 3.730MHz, 7.165, 14.224 to 14.239MHz, 21.334 to 21.346MHz, 28.680MHz +/-.  
SSTV has also been heard at the top end of 20m and 17m.  Sadly the 3.781MHz daily SSTV weather net has moved to DRM and the pictures have a fuzziness caused by excessive .jp2 compression.   On HF, SSTV should be transmitted in LSB on frequencies below 10MHz and in USB above 10MHz - the same as voice.  On 2m frequencies between 144.500 and 144.600MHz FM are used in UK and can be quite busy at times in the English Midlands.

The latest version of MMSSTV can be downloaded from the web site HERE.

N-SSTV Group (Narrow SSTV) web site HERE and on Facebook. N-SSTV Group on Facebook

SSTV Operating Tips:

1. Do not transmit half or part pictures - annoying!

2. Spread out - don't all try to have a QSO on the same frequency!  Use 1.5kHz or 3kHz spacing.  Click HERE for more information.
3. Respect digital users (FreeDV, DRM, etc) - don't cause QRM just because you can't decode the signal!
4. Do not ragchew - the SSTV frequency area is for TV, not rag chewing.  Short comments are acceptable though.
5. If there is an SSB contest try the top end of the band or even the WARC bands.
6. Do not transmit pictures that will offend other people.
7. ...and finally.....

Slant Correction

Slanted SSTV pictures are caused by differences between sound card clocks.  The sound card's sample rate may be quoted at 11025Hz but that will not be the case.  In an attempt to resolve this problem MMSSTV incorporates automatic slant adjustment.  This works to a degree but if the slant is too great because the sound card clock is way off frequency then MMSSTV can't decide which SSTV mode is in use and the received and transmitted pictures are ruined.  It is better to correct your sound card frequency rather than rely on automatic slant adjustment!  All it takes are some software adjustments!

MMSSTV is probably the most popular SSTV program out there and is also the biggest cause of the slant problem so I will attempt to give a basic guide on how to correct your sound card.  All settings are in MMSTV.

Firstly click on 'Option' then click on 'Setup MMSSTV'.  Click on the 'Misc' tab and a window should appear similar to the one shown below.

SSTV slant correction

The irrelevant options have been blurred out to avoid confusion.  You will see in the image above that the Clock has a frequency value and there is also a TX offset.  Believe it or not some sound cards have slightly different output and input frequencies!

First we will set the receive (input) frequency of your sound card.  Click on 'Adj' and another window will appear.  Tune your receiver to a time station.  In Europe RWM is really strong.  Tune to 4.995MHz USB, 4.997MHz LSB, 9.995MHz USB or 9.997MHz LSB. You should be able to hear some 1kHz pips transmitted by RWM.  If you hear a steady tone or CW then wait a few minutes and the pips should start.  Make sure your receiver is connected to your PC's Line-in or Microphone socket.

After a short time a trace of white marks should appear in the window.  These marks are the pips as received from RWM and should form a vertical line as shown below.

SSTV slant correction 

Your lines may not be as slanted as the those above or may even be slanted the opposite way - do not worry.  When you have a good line of white click at the lower end of the white line preferably on the left or right edge of it.  A thin line should appear which moves with the mouse pointer.  Now click at the upper end of the white line so the thin line follows the same angle.  Click on 'OK', the window will disappear and the Clock frequency will have changed.

Now click Adj again and expand the calibration window to full screen and repeat the above process.  Making the window bigger helps you draw an accurate line.  You will notice that the slant is less severe.  Once you are happy that the received pips form a vertical trace in the calibration window click 'OK'.  The sound card input frequency is now calibrated.

Now it is time to calibrate the sound card output!  Click on the 'TX' tab to show the window below.

SSTV slant correction

Under 'Loop back' click on 'External (full-duplex)'.  This means that your sound card's input and output will work at the same time.  Click 'OK' to take you back to the main MMSSTV window.  Connect you sound card's output to its input using a suitable lead, i.e. Headphones to either Microphone or Line-in.

Now select Martin 1 as your TX Mode and click 'TX' so that you are in effect sending an SSTV picture back to your own computer.  Once the picture has been sent click on the 'Sync' tab as shown below.  In this example I sent a blank picture just to make the sync signal obvious.

SSTV slant correction

You may notice that the sync lines are not vertical at all.  Even if they are vertical go through these steps anyway.

Click on the yellow smiley face button and the sync lines should become vertical as shown below.

SSTV slant correction

Now click on the 'TX' button which is to the right of the 'Mem' button.  Your TX offset is now set.  Just go back into 'Option', 'Setup MMSSTV' then click on the 'TX' tab to set your Loop back setting to OFF.  Your sound card is now calibrated to transmit good slant-free images.

Now you have calibrated your sound card you will transmit nice vertical images but you may still receive slanted images.  This is due to the other station not having set his sound card up properly.  So until the entire SSTV fraternity have been educated in slant-free SSTV, use the MMSSTV automatic slant correction and tell the other station they have SLANT!

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