[aprssig] APRN (Automatic Picture Relay Network) revival?

Stephen H. Smith wa8lmf2 at aol.com
Sat Aug 8 12:34:28 EDT 2015

On 8/8/2015 6:53 AM, Robert Bruninga via aprssig wrote:
> Can we go back and look at the APRN again to see if it is time to upgrade it 
> to digital, so that images can be sent end-to-end instead of posted to web pages?
> Given the same resolution of a simple SSTV (120 by 120 pixels?) how small of 
> a JPEG file can result? Shouldnt take long at 9600 baud.

120x120 is from a bygone era of 5FP7 radar CRTs being used as display devices.

The standard minimum SSTV resolution today is a 320x240 pixel (quarter VGA) 3:4 
aspect image that will yield about a 50-90K image when saved as a JPG.      
Over 99% of all SSTV today is generated and received with PC-based soundcard 
software, rather than dedicated hardware devices, and is sent with modem-like 
multiple audio tones, not as serial data that would be compatible with a 
packet-like transmission system.

What is "upgrade to digital" supposed to mean?   Classic SSTV is totally 
analog.   It's almost literally NTSC in (very) slow motion.

"Digital SSTV" as it exists today, (and is embodied in the recently orphaned 
EasyPal program whose author died of cancer around the beginning of the year) 
is essentially just a general-purpose error-corrected file transfer program.

You shove an existing image file (.JPG, .TIF, .GIF, etc) into the transmit 
routine that encapsulates it in several layers of error correction before 
transmission.  The actual over-the-air transmission uses multiple (4, 8 or 16) 
QAM audio subcarriers in the voice passband.  At the RX end, EasyPal unpacks 
the original file from it's layers of FEC and reconstitutes it as the original 
image file.   The typical transmission time is a minute or so and consists of 
the roaring grinding noise typical of multi-subcarrier data transmisions; i.e. 
like "56K modems" or digital voice.

The issue is the easiest way to capture the original live image. N1VG's (Argent 
Data) single-board SSTV cam will capture 320x240 color images and encode  them 
into your choice of several of the most popular <ANALOG> SSTV formats.  
However, the output is FMed audio tones, not logic level data.     At the 
receive end, you would use one of the common soundcard SSTV programs such as 
mmSSTV (Windows freeware) to decode and display.

I am not aware of ANY standalone hardware that will do EasyPal-style "digital" 
SSTV.   The closest I have come is running EasyPal on one of these dirt-cheap 
Windows tablets that has built-in cams.




Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

  Long-Range APRS on 30 Meters HF

High Performance Sound Systems for Soundcard Apps

"APRS 101"  Explanation of APRS Path Selection & Digipeating

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