Post date: Oct 27, 2011 4:53:37 AM
Bay Area Search and Rescue Council 2009
Chris Wong N6JGC
What is APRS?
APRS = Automatic Packet Reporting System. See positions of SAR teams in real-time on a map.
http://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System
http://www.tapr.org/aprs_information.html
For hams who want more in-depth information about APRS, see Bob Bruninga’s APRS site. This provides more information about the full spectrum of APRS communication.
In SAR applications, what equipment do I need to get on the air?
Tracker: (the transmitter unit that goes in field pack)
You must be a licensed ham radio operator (technician or higher license class) or there must be a license ham acting as a “control operator” for all stations transmitting over the ham bands. FCC requirement.
A reliable GPS that works in dense foliage capable of transmitting an NMEA text string to an RS-232 connector (DB9).
A reliable handheld 2 meter radio (144.390Mz) capable of transmitting 1 to 3W for the duration of a search. Hiigh capacity battery packs are strongly recommended.
TinyTrak 3 Plus interface device (see http://www.byonics.com/tinytrak for more details)
Interface cables for GPS and Radio, including any adapters needed
Access to a computer that can program the TinyTrak 3P interface unit
Figure 1-1: APRS Tracker set up utilizing TinyTrak3P, Yaesu FT-530, Byonics GPS2, short interface cable w/9V alkaline battery. Primary/Secondary switch included to adjust transmit rates on the fly. Components fit nicely into PMI radio chest harness from Search Gear products.
The TinyTrak, interface cables, and programming software can all be obtained from Byonics of Las Vegas, NV. See http://www.byonics.com for more information.
Internet Access:
Ability to view APRS position reports on the web at the following sites:
Exact call signs of the units to be tracked (including the suffix –n designator)
(Note: Transmitting stations must be in range of a digipeater which is tied to the Internet via IGates. In most urban areas of the Bay Area, this is not a problem. When you get into the remote area along the Pacific Coast or Sierra mountains, you may encounter limitations.)
If I want to monitor station packets directly, what do I need? (e.g. when you don’t have access to the web in the field)?
APRS Receive Station: (the receiving unit which maps the position reports on a computer)
You do not need to be a ham radio operator just to receive radio transmissions. Be sure the radio is locked not to transmit or the software is set up so the unit is not digipeating.
A Terminal Node Controller (TNC)
A reliable receive radio that can interface with a TNC – portable or mobile
Good external antenna capable of picking up weak radio signals in the field
Ground mounting (e.g. tripod) and 15 to 20 feet of masting
Computer with RS-232 (DB9) serial port or USB port with the appropriate USB-to-Serial adapter
Coax and necessary RF adapters
Necessary interface and power cables for radio
(note: A GPS is not required for a receive station)
Figure 1-2: APRS Receive Station set up utilizing Kantronics KPC-2 TNC, Kenwood TR-2500 2M HT, laptop computer and USB-to-Serial interface cable. Radio is connected to external antenna at home.
APRS Software:
The recommended software for SAR applications are:
DMapper http://www.roadfacts.com/software/dmapper/dmapperInfo.htm (shareware license required)
WinAPRS http://www.winaprs.com/ (shareware license required)
Most SAR teams are using either DMapper or WinAPRS on the Microsoft Windows platform, although WinAPRS is available for the Mac. These packages seem to be well suited for use of topographical maps. APRS Point and APRS + SA are more geared toward tracking of vehicles over a larger area. Map details are not available at the same level as the recommended programs.
What can I do to increases reliability in the field?
On average, APRS is about 70% reliable. The key factors that can increase reliability and usability are:
Good antennas and power (on both receive and tracker stations)
Rugged tracker units that can handle the elements
Extra batteries for radio and tracker
Setting up digipeating station on a high mountain top above the search area
Competent and experienced APRS users who have years of field experience in deploying and operating APRS
Dedicated computer for tracking and mapping
Where do I go to get help?
APRS for SAR applications is very much experimental. Everyone has an opinion and there are 1000 ways to make a tracker. Some folks swear by certain software programs; there functions in every software package that users hate. It all comes down to what the user is most comfortable with both with Trackers and Software.
Good sites for learning more about APRS are:
APRS for SAR is a special application, and the challenges of poor reception, extreme environment, and an emergency situation tend to favor systems which are tested, reliable, and easy to use. Folks who have actual field experience in deploying and using APRS for searches are the ones to seek out.
Feel free to contact any of the following for assistance. This list will grow as more teams gain experience with APRS.
Chris Wong N6JGC cwong78c@sbcglobal.net
Greg Carter NV6G gcarter@openaprs.net
Don Wing KG6IZS kg6izs@aol.com