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In the late nineteen fifties Copthorne Macdonald W6ZII had an interesting idea.  Slow Scan Television for Ham Radio.  He and a group of like minded friends pioneered the mode on the 11 Meter band which at the time was the only Ham band authorized for “facsimile”.  The loss of 11M to the Citizens Radio Service in September of 1958 forced the experiments to move to the 10M band where they continued with a special temporary authorization.

Early experiments with AM modulation (A5) produced unacceptable modulation sidebands and resulted in the selection of FM (F5) as the total occupied bandwidth of this mode did not exceed that of a typical 3 kHz SSB signal.  Using this modulation scheme, a series of audio tones are transmitted to convey the picture information:  1200 Hz being the vertical and horizontal synchronization tone, 1500 Hz representing black and 2300 Hz white.  Sixteen shades of gray between black and white are sent by intermediate frequency tones resulting in 128 by 128 discrete picture elements during an eight second transmit period.  Clearly this is not full motion TV as we know it.  Rather, it is a series of still frames that are “painted” from the screen top to bottom during that eight second period.   With a digital scan converter normal fast scan TV from a camcorder or other source can be converted and sent with a frame “snatched” from the fast scan video and then transmitted every eight seconds.  This is not unlike viewing stop motion animation.

Oscilloscopes using P-7 phosphors for long image persistence were replaced by digital scan converters in the 1970’s.  These allow slower frame rates to be used for increased resolution and even color transmission.  Today’s software driven soundcard decoders support an impressive array of resolution and color quality options.

This is a snap of my 1976 Robot-400 converting a TV movie to SSTV.

Carefully composed graphics have replaced live cameras for most SSTV seen on the HF bands today.

Digital SSTV can have remarkable quality.  This picture was digitally transmitted through a 2M repeater and received using the EasyPal computer program.

This picture was received on 2 Meters from the International Space Station during an overhead pass using a discone antenna and the MMSSTV computer program.

Both the analog MMSSTV program and the digital EasyPal program can be downloaded for free at the following URL’s or found using Google.

MMSSTV – http://www.qsl.net/kf6ypq/mmsstv.html

EasyPal – http://www.vk3evl.com/

Analog SSTV is found on 14.230 mHz, digital at 14.233 mHz and you can contact me for a list of other frequencies.

The Ham Radio SuitSat experiment launched from the ISS next month is expected to carry SSTV so you may want to download these programs and get ready.  Stay tuned for more SuitSat  information.

I’ll be seeing you on Ham TV!
-73 de wa6mpg

 

One Response to “Ham TV: Slow Scan Television for Ham Radio”

  1. Bryan says:

    Very cool! I’ll have to add this to my things to check out in 2011 list. Thanks Wayne

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