On Saturday, Bob N6TCY, Brian N6ZZY and myself spent the morning driving around Tracy and San Joaquin county testing APRS coverage from our portable digipeaters and an iGate. This is a report on what we think we accomplished and how we plan to proceed. In an emergency, this is the type of installation we plan to use.
APRS, for new hams, is a system for transmitting location and other information over Amateur Radio. Digipeaters — sort of digital repeaters — are to APRS the same range-extenders that analog repeaters are to voice transmissions. iGates receive packets and post them to the Internet.
One of the digis was a Kenwood TH-D72 talkie, attached to a small beam, located at the same site as the 146.655 repeater. This is a location at about 1,800 feet (as I remember) in the Altamont Hills. The beam points toward Stockton, so it is aimed a bit north of Tracy.
The mobile digi was a Yaesu FT-1500, Kantronics KPC3+, battery-powered and connected to an Arrow Antenna j-pole at about 25 feet. Bob located this digi in South Tracy, along I-580, with a commanding view of the valley. (About 300 feet in elevation).
The iGate was located at Brian’s house in Tracy, and gatewayed our RF location reports into the APRS Internet data feed. It was not be apparent to Internet users that we were not on 144.390, the national APRS channel.
Once the infrastructure was set-up, Brian and I drove around using at least two APRS radios at all times. His was a Yaesu VX-8 talkie connected to an external antenna. I used an old Kenwood TH-D7A talkie, connected to a quarter-wave mag mount antenna. We both also had Yaesu FTM-350 mobile radios shooting packets at full-power.
We are still looking over the packet logs to see what was heard by which digi from where, so that will be the subject of an update in the future.
1. A handful of users (in this case, four radios and two digis) can create an awful lot of traffic if frequent location fixes are required.
2. The iGate, connected to an outdoor antenna on Brian’s two-story house, worked great and did a fine job of making our position reports available to Internet APRS clients. It was nice to have the iGate beacon occasionally so we knew we could hear it.
3. We had a few reports from the Internet seemingly leak through the iGate and get transmitted on RF. Need to understand why that happened, but it was not a severe problem.
4. Having two digipeaters definitely improved our range, but we have to figure out which worked best where. It appears that within 8-10 miles, the local digi on I-580 picked up most of the packets, with the Altamont digi picking us up from as far as 25 miles on 5 watts.
5. We realized that none of us know as much about APRS or the settings on our radios to be really comfortable doing an exercise like this, but it was a start. Please be gentle in your comments.
6. Thank you, Northern California Packet Association, for creating the “alternate” APRS channel intended for situations where users need a quiet channel and are willing to bring their own infrastructure to get it. It is hoped that any use of the channel will be temporary in nature and permanent infrastructure will be limited. We don’t need another mess like 144.390.
We feel like we proved that the current configuration (two digis, one iGate) will work well across the Tracy area. Log analysis will tell us how well the I-580 digi worked with 5-watt signals (out to what distance?). The iGate did a good job of making us appear on Internet clients.
Speaking of which, if you have a smartphone and intact data network, apps like OpenAPRS (iOS) and APRSdroid (Android) are probably better ways to get your packets into the Internet feed than RF. However, packets sent over the Internet are generally only visible on other Internet clients. Your mobile radio operators will never see the packets generated by the smartphones. It also means that net control and others must use APRS apps and an Internet connection to see everyone’s location.
Depending on the circumstances, that may or may not pose a problem. More in a future post as we learn more.