Slow Scan (SSTV) TV via Cell Phone App!

In the past year or two I familiarized myself with the ham radio mode knows as SSTV – or Slow Scan TV.  It is called “Slow” because it is – it takes maybe two minutes to send a file.  “Scan” is in the name because the processing software operates the way a hardware based image scanner operates.  It literally processes the image file one line at a time, converting the various colors and shades of dark and light into sounds that can be transmitted by an amateur radio.  The initials “TV” are in the acronym because this is exactly the way TV cameras that you and I watch the output from at home work – one line at a time – just FAST.  So – SLOW SCAN TV – or SSTV.  Slow because it can take minutes to transmit just one image where TV transmits a LOT of images a second.  That’s FAST Scan TV.

OK – boring details are out of the way.  Most people use a computer (like a laptop or desktop) to do slow scan TV ham radio.  After doing this for some time I found an app for my cell phone (a droid) named DroidSSTV.  Yes – there are Windows apps for PC’s.  Yes – there are iPhone apps as well.  Just search Google for SSTV App (or program) and the name of your device or operating system such as SSTV App Droid or SSTV App iPhone or SSTV TV programs Windows.

Before I go too far – check-out the two photo images below:

CameraZOOM-20130628163508908     PHOTO AS RECEIVED BY WB9KMW SSTV - Hist1

The one on the LEFT is the ORIGINAL photo image direct from my Samsung Galaxy S III phone’s files.

The one on the RIGHT is one that was RECEIVED by ham radio station WB9KMW and posted on his website after receiving it via SSTV.  I used my cell phone app to do the SSTV transmission.  Here’s the cool part.  There was NO PHYSICAL CONNECTION between the cell phone and the ham radio required or used to make that transmission!

Here’s a fancy term for you…  Acoustic coupling.  That’s fancy lingo for holding your mike up to the cell phone, holding down the push-to-talk button on the mike and then starting the cell phone app to transmit the image.

On my cell phone the screen is one one side and the speaker is on the other side.  I used the edge of a desk to get as good an audio stream as possible from the cell phone.  I just put the phone down on the desk so the speaker was over the edge of the desk – being careful not to drop the cell phone.  Then I didn’t have to hold both the cell phone and the mike while I made the transmission.

DroidSSTV probably is not the ONLY phone SSTV software app out there and it may not be the best.  One thing it does lack is that ability to adjust the “slant” of the transmitted image.  Most PC software allows you to enter a number to correct for “slant”.  What is slant?  Slant is the term for a photo that seems to be otherwise fine in quality but if the photo were in a frame you could tell the photo was slanted in relation to the frame.

Please note that there are several steps to producing a received SSTV image on a website.  Each of these items and perhaps others may change the original photo – especially in analog SSTV.  In digital SSTV this is much much less the case.  Here is a list of things that can affect the quality of the image displayed on the right:

  • Noise in the phone transmitting the image.
  • Efficiency of the antenna in the phone.
  • Strength of the signal received by the ham radio station.  The signal may be distorted if the signal is too strong or distorted if the signal is too weak.
  • Antenna system used by the receiving station.
  • Local man-made noise near the receiving station.
  • Global natural noise affecting the receiving station.
  • Sensitivity and selectivity of the ham radio receiving the signal.
  • Settings in the computer connected to the ham radio station.
  • Ability of the website to accurately render the full image in accurate detail – much less of an issue with digital SSTV.
  • The monitor of the person viewing the website.

I am sure there are a few other things that can affect the final visual rendering of the photo transmitted – but you get the point.  What is sent perfectly may not, especially in the analog world, be what is viewed by the receiver or the person viewing the image on a website.

Overall, I was quite pleased with the result of my initial test of the phone app for analog slow scan TV (SSTV) for ham radio purposes.

So this is all quite fun for a hobby and personal uses.  Are there potential uses for ARES / RACES emergency communications?  Sure there are.  I can easily imagine an emergency communications scenario where normal modes of sending photo documentation of a disaster scene is impossible due to damage.  In that scenario SSTV can be used as a back-up emergency communications tool.  Clearly, digital SSTV is the first choice from the samples of received images I have worked with over the past year or two.  Digital SSTV works nicely with a laptop and a ham radio station.  Unfortunately I know of no digital SSTV cell phone apps at the current time – 2013-07-14.  Perhaps there will be some in the future.

Another thing to keep your eyes on.  There is a brand new Yaesu HT (hand held ham radio) that sports a built-in camera and a new digital mode for transmitting said photos.  I strongly suspect that this sort of technology will continue to merge and unfold into the digital realm of ham radio over the coming years and decades just as it merged in the cell phone world over the last decade.

Stay Radio Active!

73,

 

Jon Kreski – AB9NN– Appleton, Wisconsin / Green Bay, Wisconsin / Oshkosh, Wisconsin area

www.Twitter.com/AB9NN

P.S. Please visit my website www.HamRadioResources.com daily for solar weather and propagation forecasts as well as Twitter updates and fresh blog post notifications!




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