117 lines
3.3 KiB
HTML
117 lines
3.3 KiB
HTML
=== APRS
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{aprsdevices} can send APRS if desired, and the
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interval between APRS packets can be configured. As
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each APRS packet takes a full second to transmit, we
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recommend an interval of at least 5 seconds to avoid
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consuming too much battery power or radio channel
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bandwidth. You can configure the time within each
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minute that APRS transmits by changing the APRS offset
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value. When the GPS signal is locked and knows the
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current time, the APRS offset selects the time with
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each minute for the first APRS transmission;
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subsequent transmissions occur each APRS interval
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seconds thereafter. You can configure the APRS
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interval and APRS offset using {application}; that
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process is described in <<{configure_section}>>.
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AltOS supports both compressed and uncompressed APRS
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position report data formats. The compressed format
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provides for higher position precision and shorter
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packets than the uncompressed APRS format. We've found
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some older APRS receivers that do not handle the
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compressed format. The Kenwood TH-72A requires the use
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of uncompressed format to display altitude information
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correctly. The Yaesu FT1D requires the use of
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compressed format to display altitude information.
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APRS packets include an SSID (Secondary Station Identifier)
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field that allows one operator to have multiple
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transmitters. AltOS allows you to set this to a single digit
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from 0 to 9, allowing you to fly multiple transmitters at the
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same time while keeping the identify of each one separate in
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the receiver. By default, the SSID is set to the last digit of
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the device serial number.
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The APRS packet format includes a comment field that
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can have arbitrary text in it. AltOS uses this to send
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status information as shown in the following table.
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.Altus Metrum APRS Comments
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[options="header",cols="1,1,3"]
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|====
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|Field |Example |Description
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|1
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|L
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|GPS Status U for unlocked, L for locked
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|2
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|6
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|Number of Satellites in View
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|3
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|B4.0
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|Altimeter Battery Voltage
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ifdef::altusmetrum[]
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|4
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|A3.7
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|Apogee Igniter Voltage
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|5
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|M3.7
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|Main Igniter Voltage
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|6
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|1286
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|Device Serial Number
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endif::altusmetrum[]
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ifdef::telegps[]
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|4
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|1286
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|Device Serial Number
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endif::telegps[]
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|====
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ifdef::altusmetrum[]
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Here's an example of an APRS comment showing GPS lock with 6
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satellites in view, a primary battery at 4.0V, and
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apogee and main igniters both at 3.7V from device 1286.
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....
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L6 B4.0 A3.7 M3.7 1286
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....
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endif::altusmetrum[]
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ifdef::telegps[]
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Here's an example of an APRS comment showing GPS lock with 6
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satellites in view and a primary battery at 4.0V from device 1876.
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....
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L6 B4.0 1876
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....
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endif::telegps[]
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Make sure your primary battery is above 3.8V
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ifdef::altusmetrum[]
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any connected igniters are above 3.5V
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endif::altusmetrum[]
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and GPS is locked with at least 5 or 6 satellites in
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view before flying. If GPS is switching between L and
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U regularly, then it doesn't have a good lock and you
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should wait until it becomes stable.
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If the GPS receiver loses lock, the APRS data
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transmitted will contain the last position for which
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GPS lock was available. You can tell that this has
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happened by noticing that the GPS status character
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switches from 'L' to 'U'. Before GPS has locked, APRS
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will transmit zero for latitude, longitude and
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altitude.
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