What is APRS?
APRS is an amateur radio service that allows stations to broadcast their location, text messages, telemetry, bulletins and other messages. It is faciliated by digipeaters, which repeat messages, and i-gates, which listen to messages on the radio and relay them to the Internet and vice versa.
There are basically no digipeaters or igates that can hear Manhattan, which is rather sad. Under normal conditions you can just use a cellphone, but it is a problem in emergency situations. This project is for setting up a digipeater and igate on Hack Manhattan's roof.
What does a digipeater do?
A digipeater listens for messages on the APRS frequency, 144.39 MHz, and rebroadcasts them, so stations who can hear the digipeater, but cannot hear the originating station, can receive messages. Until we have a more powerful transmitter, a much better antenna or a higher elevation, there's probably not too much point to this. On the other hand we are higher up than HTs at street level.
What does an igate do?
An igate does two things. It listens to messages on 144.39 MHz and sends them to APRS servers on the Internet, so they are available at aprs.fi. This can be helpful to view location data, or to relay messages. There are several APRS-to-email gateways out there.
An igate can also receive messages from the APRS Internet servers and send them out on the radio. This is typically done if knows that the receiving station is nearby. In this way APRS text messages can be sent from any station to any other station as long as both are close to functional igates.
We can use a Raspberry Pi with a USB sound card to interface to the radio. We will start with a Wouxun HT with a high gain antenna and a quarter wavelength counterpoise. Later we could upgrade to a mobile transceiver that can put out more power, such as the Kenwood TM-281A ($144.95 with coupon), but with a good antenna the Wouxun should be heard through much of Lower Manhattan and Brooklyn.