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