Automatic Picture Relay Network
Bob Bruninga, lastname at usna dot edu
APRN is a concept that should revolutionize the use of amateur radio in support of emergencies, special events and public service. It allows mobile, portable and handheld operators to send back live images from the field for real-time review by anyone, anywhere, using ANY radio! Prior to APRN, images could be sent from one SSTV station to another, but since fewer than a fraction of 1% of ham operators had SSTV capability, there was no way to get the image from the receiver to the person, VIP, or agency that needed it.
All of that changed in the early 2000's with the advent of SIX powerful Ham Radio technologies that had coalessed in the last few years:
The APRN Concept: The APRN Concept is simple. One takes an image using any smartphone or other SSTV camera, then enters the title and any comments into a MESSAGE to APRN on their APRS radio. Then they go to the local APRN frequency in their area and send the packet. When it is acknowledged by APRS message, then they activate their SSTV ap and send the image audio over the same radio. The APRN receiver then places the image on the local APRN Web page and it is available for anyone to see on the APRN web page. It also sends out a NEW IMAGE announcement on the local APRS channel so all APRS users in the area can see it.
AND/OR, any other ham with an SSTV application can go to that same local frequency and with an APRS message, request any image that is on file. Thus, we have real-time critical image exchange over ham radio independent of the cell phone network - usable in emergencies or when networks are down.
KEN-CAM (Kenwood VC-H1): Although SSTV has been around for 50 years or more, it had always been a relatively boring exchange of pre-captured images between hamshacks. In the late 1990's, Camera interfaces existed, but it still required a PC or other large appliance to convert the image to SSTV. The arrival of the Kenwood KEN-CAM (VC-H1) in 1997 (shown at right), completely changed the playing field, since the entire image system fit in a shirt pocket or the palm of your hand and could be used anywhere when plugged into the companion APRS hand held also shown here. This was a full decade before cell phones started adding cameras. This, combined with the public's general acceptance of still-frame video over the internet totally embraced a complete paradigm shift to a totally new real-time in-the-field imaging capability.
SMART Phones and Tablets are NOW: Unlike in 1990's when only a fraction of 1% of hams had a VCH1 handheld SSTV device, now in the decade since 2010, almost everone now has a smart phone or tablet with built in disply and camera that can with the right application, send and receive images from anywhere at any time via the wireless system. But the importance of the APRN network is that it takes this one step further when the cellphone is out of network. Then the same phone can be held next to a Ham Radio HT and just by audio coupling, can send and receive the image via the SSTV application.
Here are some smart phone SSTV Aps that anyone can use:
SSTV Transmissions from the ISS: For the past several years, an SSTV transmitter has been on the ISS and is activated occasionally for special events. These SSTV applications can all receive these images with norhing more than an FM radio or walkie-talkie. See SSTV from ISS And also KO6KL's live HF SSTV web page
APRS HT (Kenwood TH-D7) The key to the automation of the WEB PAGE interface for APRN is the availability of text messaging in any of the APRS walkie-talkies. . These radios, without a computer, or any external components, allows a user to send a packet identifier for the subsequent transmitted SSTV audio image. This packet message contains a machine readable single packet identifier that includes the CALLSIGN, LOCATION, TIME, TITLE, Direction and field of view of the image!
APRS IMAGE IDENTIFICATION: The keypad on the APRS HT can be used for entering the necessary alphanumerics and the built-in TNC then transmits it. Since the APRS radio also knows its position, then the LAT/LONG of the SSTV image is also automatically included! Thus you can transmit the WHO, WHAT WHEN, and WHERE needed for full automation of the WEB page for cataloging and indexing real-time images from multiple remote users.
POSITION REPORTING: The existing worldwide APRS.FI network serves as the GEO-POSITION locator system for APRN to show WHERE the images were taken in real time.
APRN NETWORK The APRN network is not really a network at all. It is only a web page that captures uplinked images and applies the APRS transmitted identifying information so that the SSTV images can be indexed and sorted by location, call, time, or event. These local APRS sites can be set up on any locally designated frequency in cities everywhere for SSTV images to be uplinked to the nearest APRN node which then hosts the images as WEB pages. These local networks can be as simple or complex as needed to provide the mobile converage needed. ANyone can find them, since they identify themselves with a FREQUENCY OBJECT on the local APRS channel. A few examples follow:
FREQUENCIES: Frequencies are a local issue only. Typically, only one frequency is needed and it can be shared with other applications. ALso, since only mobiles or remotes uplink on the channel in simplex to the APRN receiver, any simplex frequency can be used. There is no need for the APRN site to transmit anything on the channel back to the user other than a brief 1 second acknowledgment. Thus it is consistent with simplex shared use.
APRN FORMAT: The value added to SSTV by the APRS identification packet cannot be over emphasized. Without this human readable data, the SSTV image is just an un-identifiable picture. But with an APRS packet identifier, then the picture becomes so much more valuable. . All of the following information is added to the picture with APRS:
APRS SSTV SYMBOL: Since 1997, APRS has a well defined SSTV symbol "/T". . Any station sending a packet as an SSTV image identifier packet, should use this symbol. All of the above fields are self explanitory except for the DIRECTION and FOV. . It is proposed that for this symbol and this application, that the normal CSE/SPD field of the packet be interpreted not as CSE/SPD but as DIR/FOV. . The use of CSE to indicate the direction the camera is pointing is relatively straight forward. But we can use the SPD field to include the width of the FOV in degrees. . There is no loss of significance to the actual CSE and SPD fields, because if this packet is being used to identify a picture, then CSE and SPD are meaningless in this context. But DIR and FOV are very valuable. . Imagine an APRS map that can not only show the location that an image was taken, but also the camera direction and FOV with an overlayed WEDGE!
GLOBAL APRN ACCESS: All of the above items of information associated with the image are transmitted in the initial packet by the originator. This is what any APRS packet station wouild capture if he were monitoring the original packet. . But the real value-added by the local APRN-Receiving node is the archiving of that image and that data for on-line retrieval by anyone, anywhere via the internet. In that regard, the APRN takes the originators original APRS packet, parses out the information and after archiving the data, it then re-formats the data into a new standard APRN packet onto the APRS-IS but with the addition of "//URL..." on the end. This "//URL..." is the full URL of the now-saved image. . THis packet being injected into the APRS global Internet System (APRS-IS) is now available anywhere in the world. . The following OBJECT format is suggested:
Where the original image is number nnn originated by WB4APR, and it was received by the KB2SCS APRN node at DDHHMMz and injected into the APRS-IS as an object with these fields:
That makes the image then available worldwide within the APRS-IS system by the simple reference to the APRS object "WB4APRnnn" and then its URL.
de WB4APR, Bob
NOTE! These pages are NOT yet automatic. The purpose of this APRN web page is top show what we COULD do with SSTV.