Thursday, July 9, 2009


Blog Post 6 – MMSSTV—Slow Scan Television software by Makoto Mori, JA3HHT – Introduction to analog image transmission

Wednesday July 15, 2009

This is Curt Black, WR5J with the Educational Radio Net – No digital QST tonight so we can get everyone set up and running with MMSSTV.

Slow Scan TV (SSTV) is a way to get the high-information density of visual images shoe-horned into the audio-bandwidth typically used by the human voice of about 2.5kHz. Bandwidth for full motion NTSC video requires about 4.5Mhz or 9.0 if you use both sidebands as you transmit– so minimally a bandwidth ratio of about 2000/1.
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On slow-scan TV we do this by sending just a single image and spreading that single image out in time. It typically takes from 8 seconds (Robot Grey-scale 160x120) to 269 seconds (ScottieDX RGB 320x256) to transmit an image. And you probably noticed that those images are way smaller than the 525 lines of an NTSC video. It seems like a lot of fuss, but images are powerful things, capable of communicating easily more than the typically cited, “1000 words” of meaning. Like the one at the top of this blog post of the Seattle Library from a recent Simulated Earthquake response for Seattle ACS.
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Just like the RS-ID being implemented by our digital modes, SSTV uses a standard burst at the beginning of the transmission called VID to allow the software to decode using the correct format. The details of that signal are appended to the end of the Yahoo Group MMSSTV Setup and Use compilation.
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Just like an NTSC TV picture, the SSTV signal is built line by line and point by point. In contrast to the digital pictures we will do next week with EASYPAL, the information is built by capturing the audio information and correlating a particular brightness with a particular audio frequency.
To start each line, a sync pulse is sent at 1200 Hz. There is one of these per line, so you should be able to see a peak at 1200 Hz in the energy in the spectrum display. The brightness information is sent between 1500 and 2300Hz. As the picture is being transmitted, you will see clearly this band of frequencies being received.
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To tune in the station on HF-USB, just adjust your main tuning dial to place the sync pulse at 1200. MMSSTV and all the other programs provide markers at 1200, 1500 and 2300Hz. to make this easy.
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To use this software, just go to the SSTV watering holes such as 14.230 or 14.233. This is the best know and possibly the best defended frequency in all of amateur radio. I enjoy listening during contests as someone innocently goes in to call CQ.
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One weakness with this software is its identification of different sound cards. The more you have the harder it is to find it because there are only numbers – no names. You just have to try one number after the other until you are receiving.
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For the receive side of this software, you would typically leave the AUTO box checked, but if you don’t start to receive the signal automatically, you can try SCOTTIE 1 or 2 – the most often used modes in North America. If you are receiving DX from Europe or Japan, try MARTIN 1 or 2. Most operators give a voice ID at the beginning of their transmission where they announce the mode being used, although that can be lost in the noise if the stations aren’t strong. You can definitely decode and see adequately signals from stations too weak to allow copy of a voice signal.
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To learn more about this mode or ask questions about the software, check out the Yahoo Group http://groups.yahoo.com/group/MM-SSTV/
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To check out activity on the bands or see what has been transmitted recently, check out http://www.g0hwc.com/ G0HWC has sites for Analog and Digital SSTV and links to the software as well as helpful discussion.
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Onward to getting the software setup:
OK, This part isn't working since I can't get the images in the right place - please go to the http://groups.yahoo.com/group/wa-digital/files/
area and snag the Blog Post #6 and see what this was supposed to look like... vy sri.
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1. Download MMSSTV from http://mmhamsoft.amateur-radio.ca/mmsstv/
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2. Install MMSSTV, and work through these instructions. Add your callsign when prompted.
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3. Shut down all other programs you might have running, then start MMSSTV and select the OPTIONS pull down from the top tool bar.
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4. Select SETUP MMSSTV(0) from the pull down
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5. This will bring up a three tabbed window, select the RX Tab.
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6. Set up the RX Page as follows, (DO NOT CHANGE THE LEVEL CONVERTER INFO):
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7. Set up the TX Page as follows, (DO NOT CHANGE THE TxBPF/TxLPF, TUNE BUTTON INFO, or PORT value):
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8. Set up the MISC page as follows, (DO NOT CHANGE THE FIFO, or DEVICE ID):

9. Note above: DO NOT change anything in the CLOCK window yet.
10. Once you have these items set up calibrate the software to your clock setting by the following procedure:
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Clock calibration
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In SSTV, errors in the timing of the clock appear as a slanted image. For MMSSTV, you are not required to have the absolute and exact clock frequency value (e.g. 11025Hz). But it is important to get MMSSTV informed of the discrepancy of your soundcard to a standard.
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In normal situations, you would only have to adjust the slant by using the Sync window. If you want to calibrate your soundcard very accurately, listen to a standard radio such as WWV, CHU or JJY.
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1) Go Option, Setup, Misc page, and push Adj button.
2) Receive standard radio signal (e.g., WWV and JJY).
3) Tune into the tick sound.
4) Continue listening to the sound for a while. You have a vertical line.
5) Click the upper point of the line.
6) Click the lower point of the line.
(these instructions actually show up in the calibration window)
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An alternate method is to locate a station that believes they are calibrated correctly. They become the "Standard" for you and all who come after you. Clearly the problem with this is it can become a “blind leading the blind” situation with errors propagating through the community. Cleary if you are willing to do the calibration above you will have done your part to make the world a better place.
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11. However, for the non-WWV technique, have the “standard” station send a picture to you. After that picture is complete move to step 12.
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12. Select the "SYNC" tab, (you can do this while the picture is being received), then select the NICONICO (Happyface), button ONLY after the picture is complete. A number will appear in a small white box in the upper part of the screen. This is your error from the selected "Master" station.
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13. You may press the "MEM" button. This will lock your computer to the "Master" stations clock frequency. Your receive is now setup.
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Operation:

First you need to get some images to work with. Luckily nothing could be simpler. In MMSSTV, click on the RX tab toward the top of the screen and the S.pic tab at one third up from the bottom. There is room for some 300 photos in this Stock Pictures area.
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Open a Windows Explorer/File Manager window and open the folder where you have some images. Select an image and drag it onto the icon on the taskbar for MMSSTV until MMSSTV opens, then continue dragging to one of the open frames along the bottom of the screen. Drag in as many as you find interesting and which you might want to share. Colorful, active photos are best, but standard images of rigs and operators are fine, too.
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Set up your Com Port – check your Port assignments by getting to where you can see MY Computer – right click and select Properties –on the window that opens, click the Device Manager tab in the middle of the window. From the list that appears, click on the Ports (COM and LPT) icon and look through the resulting list of ports for the one assigned to your radio PTT. It is certainly possible to brute force try one after another if you can’t get it another way.

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That could be it – click the TUNE button and adjust the transmitter for 50% or less of your full power rating for the radio you are using (SSTV is 100% duty cycle – pretty much key down for 90 seconds or more - far more than your voice requires of the equipment – don’t toast your radio.
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For more details of the mode, check out the SSTV- MMSSTV-How-To-Set-Up-Doc on the Yahoo Group site for WA-DIGITAL. It starts out with duplicate info as this blog, but then goes into more specifics on the mode and operating.

Next week we will contrast tonight’s work with MMSSTV and analog image transfer with EASYPAL – digital image (and much more) transmission. EasyPal is an amazing program. The software is on the WA-DIGITAL site as will be a setup document really soon. Please download it and install it before next week’s session.

See you on the waterfall – or right on my screen!

VY 73 DE WR5J

Curt Black

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