How To Make An APRS WIDEn-N Digipeater
Current "standard"
1200bd VHF APRS Digipeater System
+ 
+
+ 
October, 2009: Until recently there wasn't much need for this page, as there was simply one best solution to putting together a mountaintop APRS WIDEn-N digipeater. The equipment was simple: a power supply, just about any 2m mobile radio tuned to 144.39, a Kantronics KPC-3+, and decent antenna. For those sites lacking "shore" power, the mobile radio could be swapped out with a handheld, like the ever-trusty Radio Shack HTX-202 and a solar panel, and that would work just fine as long as the distance to the antenna was no so great so as to bring in the signal loss factor. When it comes to antennas, consideration must be given to wintertime weather conditions at the site. Clearly a home-type antenna won't survive one blistery winter atop a mountain. The overall cost is about $600. In return you get a WIDEn-N for 1200bd APRS. Added note, your site location may require filters or cavities, at added expense.
New 9600bd UHF APRS Digipeater System
+ +
+
In the quest for 9600bd APRS solutions, Bob King/K7OFT in Seattle, has taken the lead and established a high(er) speed system on 440.800 UHF. There are several digipeaters and home stations, and a growing number of people enjoying the much-shorter packets, offering room for growth in the Puget Sound area. The system components for a 9600bd UHF APRS digipeater are somewhat similar to the defacto standard. There is a power supply, UHF mobile radio (one that will work with 9600bd packet, as not all do), a Kantronics KPC-9612 TNC (does both 1200bd and 9600bd), and a UHF antenna. Typical cost is about $800-$900 because UHF radios are more expensive than VHF radios, and the KPC-9612 is about double the cost of a KPC-3+. Note, this is a standalone 9600bd UHF digipeater, and has no connection to the standard 1200bd VHF APRS system. Several home stations on the network, also using a KPC-9612 and UHF radio, share the data with the APRS-IS so it is available on FINDU and other internet sites. The 440.800 9600bd system responds to an outgoing path of WIDEn-N, just like the primary 1200bd VHF frequency.
New Combo 1200bd/9600bd VHF APRS Digipeater System
+
+
+
In further experimentation for 9600bd APRS, Scott/N7FSP, also in Seattle, has had similar excellent results at high(er) speed APRS on 144.35 VHF. Scott has access to really great mountaintop locations, and has developed a dual-function system supporting 1200bd APRS on 144.39, and adding 9600bd APRS on 144.35 by using a Kenwood D710 dual-band mobile radio. His configuration uses the 9600baud built-in TNC on the A band of the radio (left side) on 144.35, and uses either an external Kantronics KPC-3+ or Argent OpenTracker2 1200bd TNC and programmed with the B band (right side) on 144.39. The beauty of Scott's configuration should be pretty apparent for those who already have a 1200bd VHF APRS digipeater in place, and that is, to add 9600bd support on 144.35 the only additional component is the Kenwood TM-D700 (at a cost of about $500). If there are cans or filters in use, those should work just fine with the new configuration. As it's all VHF, the antenna does not need to be replaced. You'll remove your existing radio and relegate it to other uses, perhaps at home for connected to the KPC-9612 and tuned to 144.35 to have an existence on both 144.35 9600bd and 144.39 1200bd. The 144.35 9600bd system responds to the default outgoing path WIDE1-1,WIDE2-1 for mobiles, WIDE2-2 for fixed stations, and WIDE2-1 if it flies.
Pinout for the cable between the radio and TNC can be found on page 37 of the D710 manual.
Why Do We Need 9600bd APRS?
Most larger metropolitan areas, those with more than 100 APRS users, are no doubt aware the 1200bd system is over-saturated with normal use, people out driving around sending position reports every minute, those with home or office stations on 30 minute beacons, the WIDEn-Ns supporting the infrastructure, and whatever other data that's being introduce at the RF or internet feed. If you turn up the volume on 144.39 in the Puget Sound region, you don't hear much of a break between the packets. In order to continue the growth of APRS, we needed to come up with a solution that gives the 1200bd system a rest. We've had some success with developing an additional frequency also at 1200bd, and suggesting users with low-powered trackers use it to get into the system, and at the same time was experimenting with 9600bd APRS to determine its effectiveness and usefulness. As more radios are being manufactured, supporting 9600bd packet, the light really came on when it was apparent that many more stations, and much more data could be shared amongst the users in a 9600bd environment. Thanks to Bob and Scott for proving 9600bd APRS can, and does work GREAT.
One other consideration we've been investigating, if there is a common UHF frequency than can be used anywhere in North America. The Puget Sound effort is on 440.800Mhz, but we've already determined the frequency is dedicated for other use in areas outside Puget Sound. We don't know if we can come up with a common UHF frequency. On VHF, 144.35 appears pretty wide open for further development with 9600bd APRS, and Scott working pretty quickly to expand this system, and bring some new users in along the way.
Where Do We Go From Here?
We'll continue development with both the 9600bd VHF and UHF systems in the Puget Sound region. Other areas are encouraged, and welcomed to join in and add to either system. For those with APRS digipeaters already in place, my recommendation is a co-existent 1200bd/9600bd VHF system such as Scott is building. It's a logical next-step in our quest for higher-speed APRS, and making room for others to join in.
For the most part, people use APRS for fun. There are several Search and Rescue groups who take the technology a little more seriously, and have a useful application for APRS, but for the most part, we turn our trackers on, or watch the screen at home and see who's out there moving around. Some people have trackers in their airplanes and helicopters, others deploy trackers in high altitude balloon projects to make sure they get their stuff back, while others drop trackers on bicycles or parade floats for public service events. The APRS station at the state EOC at Camp Murray remains in operation, but hasn't had much use in the past couple years. Several years ago APRS was used extensively to help track the status of wildland range fires in the Yakima area. I can't help but think there's more we can be using APRS for, and some of it is perfect for the 9600bd system that's being deployed now.
If you have comments, please address them to Dave K7GPS, at k7gps@arrl.net. Thanks for reading.