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+	=== APRS
+
+		{aprsdevices} can send APRS if desired, and the
+		interval between APRS packets can be configured. As each APRS
+		packet takes a full second to transmit, we recommend an
+		interval of at least 5 seconds to avoid consuming too much
+		battery power or radio channel bandwidth. You can configure
+		the APRS interval using {application}; that process is described in
+		<<{configure_section}>> in the {application} chapter.
+
+		AltOS supports both compressed and uncompressed APRS
+		position report data formats. The compressed format
+		provides for higher position precision and shorter
+		packets than the uncompressed APRS format. We've found
+		some older APRS receivers that do not handle the
+		compressed format. The Kenwood TH-72A requires the use
+		of uncompressed format to display altitude information
+		correctly. The Yaesu FT1D requires the use of
+		compressed format to display altitude information.
+
+		APRS packets include an SSID (Secondary Station Identifier)
+		field that allows one operator to have multiple
+		transmitters. AltOS allows you to set this to a single digit
+		from 0 to 9, allowing you to fly multiple transmitters at the
+		same time while keeping the identify of each one separate in
+		the receiver. By default, the SSID is set to the last digit of
+		the device serial number.
+
+		The APRS packet format includes a comment field that can have
+		arbitrary text in it. AltOS uses this to send status
+		information about the flight computer. It sends four fields as
+		shown in the following table.
+
+		.Altus Metrum APRS Comments
+		[options="header",cols="1,1,3"]
+		|====
+		|Field	      |Example	      |Description
+
+		|1
+		|L
+		|GPS Status U for unlocked, L for locked
+
+		|2
+		|6
+		|Number of Satellites in View
+
+		|3
+		|B4.0
+		|Altimeter Battery Voltage
+
+		|4
+		|A3.7
+		|Apogee Igniter Voltage
+
+		|5
+		|M3.7
+		|Main Igniter Voltage
+
+		|6
+		|1286
+		|Device Serial Number
+		|====
+
+		Here's an example of an APRS comment showing GPS lock with 6
+		satellites in view, a primary battery at 4.0V, and
+		apogee and main igniters both at 3.7V from device 1286.
+
+		....
+		L6 B4.0 A3.7 M3.7 1286
+		....
+
+		Make sure your primary battery is above 3.8V, any
+		connected igniters are above 3.5V and GPS is locked
+		with at least 5 or 6 satellites in view before
+		flying. If GPS is switching between L and U regularly,
+		then it doesn't have a good lock and you should wait
+		until it becomes stable.
+
+		If the GPS receiver loses lock, the APRS data
+		transmitted will contain the last position for which
+		GPS lock was available. You can tell that this has
+		happened by noticing that the GPS status character
+		switches from 'L' to 'U'. Before GPS has locked, APRS
+		will transmit zero for latitude, longitude and
+		altitude.