This system monitors 146.700 simplex on 2 meters and 438.150 on UHF for SSTV transmissions from mobile units or remote locations throughout the greater Los Angeles area 24 hours a day . The picture transmission can be followed by an APRS Mic-E packet data burst containing GPS-based position information. The SSTV picture is received at my fixed station in Pasadena, California, decoded, and automatically uploaded to this website.
If the SSTV transmission is followed by APRS data, the packet burst is decoded and the position plotted on a map. This map, showing where the picture was sent from, is uploaded to the website along with the picture. If no APRS packet data is received, the map will show the location of my APRN receive site in Pasadena instead of the sender's location.
NOTE: The simplest way to combine SSTV and APRS transmission is to use a Kenwood D700 or D710 transceiver with built-in APRS capability. Feed the SSTV signal into the rear-panel 6-pin mini-DIN "DATA/PACKET" connector (details here) of the radio. Use the radio's configuration menu to set the APRS beacon mode to "PTT" instead of the usual "AUTO" mode. In this mode, an APRS position burst is sent each time the radio is unkeyed after a voice transmission. Each time your SSTV hardware or software keys up the radio to send a picture, an APRS position burst in Mic-E format will be sent automatically after the end of the picture transmission.
An alternative would be to use a Byonics TinyTrack encoder (details here) set to Mic-E mode, with any VHF or UHF FM radio. Connect the Tiny Track's TX audio out in parallel with the SSTV TX audio into the radio's mic jack (or mini-DIN DATA/PACKET connector if the radio has one).
correct for errors in the send and receive sample rate of computer sound
systems used in SSTV is essential. If not corrected, SSTV pictures WILL
be transmitted slanted, lose sync or even fail to display at all in the
other stations software. Numerous images shown on the
APRN server are slanted because the transmitting station HAS NOT
CALIBRATED their sound card properly. The 96K Windows-based
calibration utility, downloadable below, will measure the RX and TX errors
and yield a number that can be entered into the correction dialog boxes
present in every SSTV program. Note that this program may have
to run for 15-30 minutes before converging on a final error
value. Utility courtesy of the
MixW software development group at http://mixw.net
The system consists of APRN software by KB2SCS, mmSSTV , and UI-View32 all running on a VIA EPIA-TC micro-ITX 12VDC-powered motherboard. My ham radio "SuperServer" system that combines the computer, TNCs, radios and interfaces into a single package is described here.
Receive audio from a 2M FM transceiver is coupled into the PC's sound input through a homebrew soundcard interface described elsewhere on this site for SSTV reception. The same audio is also coupled into a Kantronics KPC3+ TNC connected to the PC's serial port to decode the APRS packet bursts. The received SSTV image is automatically saved as a JPG file to the PC's hard disk. The screen showing the map with the APRS position report (if sent) is captured and saved to a 2nd JPG file.
The APRN application updates an HTML file listing the time and date of each picture. It then uploads all three files (the 2 JPGs and the HTML file) to my website via a cable modem connected to the PC's built-in Ethernet interface.
The machine described below was formerly used in the APRN system. It has been superseded by the "SuperServer" described above.
This is a complete desktop PC in a package barely
larger than 4 CD jewel cases stacked on top of each other. This machine has a 1 GHz
Celeron processor, 256MB RAM, 60 GB hard drive, built-in 100MB/sec Ethernet interface,
built-in 56K modem, XGA and S-video outputs, sound system with built-in speaker and
hardware volume control, standard PS/2 mouse and keyboard inputs, 2 USB ports and 24X
The MiniBook is based on laptop-type hard drives, small-outline DIMM memory, and slimline CD drives -- you can think of it as a "laptop without a display". The unit is made in Taiwan and is distributed in the US by Cappuccino Computer (US arm of the manufacturer). The Pentium 4 descendents of my PC are described on this page of the site.
The unit is powered from a laptop-style external power "brick" and only draws about 24 watts -- perfect for 24/7 operation. I power it using a 12-VDC-in/18 VDC-out "laptop car adapter" running off my ham shack 12VDC battery plant/charger system for totally uninterruptible power.