time, and would of course appreciate customer feedback on
performance in higher altitude flights!
</para>
+ </section>
+ <section>
+ <title>APRS</title>
<para>
TeleMetrum v2.0 and TeleMega 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.
+ battery power or radio channel bandwidth. You can configure
+ the APRS interval using AltosUI; that process is described in
+ the Configure Altimeter section of the AltosUI chapter.
+ </para>
+ <para>
+ AltOS uses the APRS compressed position report data format,
+ which provides for higher position precision and shorter
+ packets than the original APRS format. It also includes
+ altitude data, which is invaluable when tracking rockets. We
+ haven't found a receiver which doesn't handle compressed
+ positions, but it's just possible that you have one, so if you
+ have an older device that can receive the raw packets but
+ isn't displaying position information, it's possible that this
+ is the cause.
+ </para>
+ <para>
+ 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.
+ </para>
+ <table frame='all'>
+ <title>Altus Metrum APRS Comments</title>
+ <?dbfo keep-together="always"?>
+ <tgroup cols='3' align='center' colsep='1' rowsep='1'>
+ <colspec align='center' colwidth='*' colname='Field'/>
+ <colspec align='center' colwidth='*' colname='Example'/>
+ <colspec align='center' colwidth='4*' colname='Description'/>
+ <thead>
+ <row>
+ <entry align='center'>Field</entry>
+ <entry align='center'>Example</entry>
+ <entry align='center'>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>1</entry>
+ <entry>L</entry>
+ <entry>GPS Status U for unlocked, L for locked</entry>
+ </row>
+ <row>
+ <entry>2</entry>
+ <entry>6</entry>
+ <entry>Number of Satellites in View</entry>
+ </row>
+ <row>
+ <entry>3</entry>
+ <entry>B4.0</entry>
+ <entry>Altimeter Battery Voltage</entry>
+ </row>
+ <row>
+ <entry>4</entry>
+ <entry>A3.7</entry>
+ <entry>Apogee Igniter Voltage</entry>
+ </row>
+ <row>
+ <entry>5</entry>
+ <entry>M3.7</entry>
+ <entry>Main Igniter Voltage</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ <para>
+ 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.
+ <screen>
+ L6 B4.0 A3.7 M3.7
+ </screen>
+ </para>
+ <para>
+ 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.
+ </para>
+ <para>
+ 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.
</para>
</section>
<section>
<title>Configurable Parameters</title>
<para>
Configuring an Altus Metrum altimeter for flight is very
- simple. Even on our baro-only TeleMini and EasyMini boards, the use of a Kalman
- filter means there is no need to set a “mach delay”. The few
- configurable parameters can all be set using AltosUI over USB or
- or radio link via TeleDongle.
+ simple. Even on our baro-only TeleMini and EasyMini boards,
+ the use of a Kalman filter means there is no need to set a
+ “mach delay”. The few configurable parameters can all be set
+ using AltosUI over USB or or radio link via TeleDongle. Read
+ the Configure Altimeter section in the AltosUI chapter below
+ for more information.
</para>
<section>
<title>Radio Frequency</title>
frequency to successfully communicate with each other.
</para>
</section>
+ <section>
+ <title>Callsign</title>
+ <para>
+ This sets the callsign used for telemetry, APRS and the
+ packet link. For telemetry and APRS, this is used to
+ identify the device. For the packet link, the callsign must
+ match that configured in AltosUI or the link will not
+ work. This is to prevent accidental configuration of another
+ Altus Metrum flight computer operating on the same frequency nearby.
+ </para>
+ </section>
+ <section>
+ <title>Telemetry/RDF/APRS Enable</title>
+ <para>
+ You can completely disable the radio while in flight, if
+ necessary. This doesn't disable the packet link in idle
+ mode.
+ </para>
+ </section>
+ <section>
+ <title>APRS Interval</title>
+ <para>
+ This selects how often APRS packets are transmitted. Set
+ this to zero to disable APRS without also disabling the
+ regular telemetry and RDF transmissions. As APRS takes a
+ full second to transmit a single position report, we
+ recommend sending packets no more than once every 5 seconds.
+ </para>
+ </section>
<section>
<title>Apogee Delay</title>
<para>
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