John Wells, M5AML. QTH: Derby, IO92GW.

KG-STV - A DIGITAL SSTV SYSTEM BY JJ0OBZ

 

KG-STV is a digital SSTV system developed by JJ0OBZ.  Images are split into blocks of 16x16 pixels which are compressed then transmitted.  All images are 320x240 just like some analogue SSTV modes.   KG-STV only uses 600Hz bandwidth and errors in the received image, due to fading, QRM, etc., can be corrected by sending a Bad Segment Report (BSR) back to the originating station which can then retransmit the required blocks to complete the image.  Short text-based messages can also be sent.

KG-STV TX Window


Above you can see the KG-STV window.  On inital start up click on "Settings" to set up your sound card, callsign, waterfall colour etc.  Most of the options on the right-hand side of the Settings window can be left alone.  "Image Block Scan Direction" determines how the 16x16 blocks are transmitted, horizontally (similar to SSTV), vertically, or randomly.  KG-STV is clever enough to know which block goes where so this setting does not have to match the setting at the receiving station.  Once all options are configured correctly click OK to return to the main window.

Drag and drop an image into to right-hand box or click "From Clipboard" to paste an image from clipboard.  In the screenshot above I pasted a picture of a bird.  The image will be compressed and the time it will take for the picture to be transmitted will be displayed below the image  - 2 minutes, 24 seconds in the example above.

Clicking on the "Mode" drop-down menu allows you to choose between "MSK" and "4L-MSK".  Four level MSK is faster than MSK but more errors may occur.  The "Code" drop-down menu lets you choose from "Normal" or "Convolution" encoding, the latter being more robust so is less prone to errors, but is also slower than the "Normal" setting.  Finally the "Scale" drop-down menu lets you determine how much JPEG compression is applied to your image.  Too much compression my degrade to image quality and too little may result in an annoyingly long transmit time.  As you adjust the settings in these menus you will notice that the "TxTime" figure alters accordingly.  "MSK - Mode" and "Normal - Coding" are probably the best settings for use on the 20m band.  Whatever settings you choose for transmission of an image will be detected automatically be the receiving station.

When you are ready to transmit your image click on "Send Image" and transmission will commence.

KG-STV Transmitting a picture

As the image is transmitted it builds up in blocks in the "TX" window.  The screenshot above shows the bird picture being received block by block in the receiving station's "RX" window.  The callsign, transmission mode (NORM MSK), transmission type (IMG) and compression scale (1.00) of the transmitting station are shown below the waterfall display.  The little box below the image shows which blocks have been received correctly, are corrupted, or are missing.  A green dot means that the block was received correctly, red means corrupted and black signifies a missing block.  In the example above only part of the image has been received so far because the transmission is in progress but the blocks that have been received are all error free, so the top part of the box is green and the lower section is black.

KG-STV Corrupted Image


Now in the example above you can see that the transmission has ended but the received image has both missing and corrupted blocks - note the red and black areas in the bottom right-hand box.  The "Send 36 BSR" button has appeared on the left-hand side of the window which means that a BSR can be sent to the station who sent the image initailly.  This will enable the other station to send you the 36 blocks you require to repair the image.  When the other station receives a BSR the "Resp 36 BSR" button (Respond 36 BSR) will appear and on clicking this button the required 36 blocks will be retransmitted and the recipient should see a perfect image.  All received images are stored in an Autosave folder within the KG-STV folder.

As you can see in the screenshot below the received picture has now been repaired and all blocks are shown as green.  The images stored in the Autosave folder can be viewed by clicking on "LOG" then using the left and right arrows to flick through the images.  You will also notice in the screenshot below that a text message has been received.  To send one of these type your message in the white box adjacent to the "Send Text" button then click "Send Text".


KG-STV Repaired Image and Text Message

I have tested this software on a 1.6GHz Dual Core Windows XP SP2 system and on a 366MHz Pentium II Windows 98SE system and it works on both systems very well indeed.  I can see this mode being quite a success mainly because the software is easy to use, it requires less processing power than DRM and images are of standard SSTV size.  I would like to see more picture resolutions available such as 320x256, and 640x496.  An MMSSTV user interface would be great or incorporation of KG-STV in the MMSSTV software would be superb.

The suggested frequencies for HF are 3.733MHz LSB and 14.233MHz USB and around the usual SSTV allocations on other bands.  Do take care not to cause QRM to DRM or SSTV users.  There is a lot of KG-STV activity on 14.233MHz now as well as the usual DRM and analogue signals, so some people QSY to 14.236MHz

JJ0OBZ's KG-STV website in Japanese is HERE KG-STV can be downloaded directly HERE and there is a Yahoo Group HERE.

As an example of received picture quality here are some pictures I have received on 20m using KG-STV:

KG-STV Received Image IZ1MKE KG-STV Received Image IZ1MKE

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