--- /dev/null
+[appendix]
+== TeleGPS System Operation
+
+ === GFSK Telemetry
+
+ TeleGPS's native telemetry system doesn't use a
+ 'normal packet radio' mode like APRS because it's not
+ very efficient. The GFSK modulation we use is FSK
+ with the base-band pulses passed through a Gaussian
+ filter before they go into the modulator to limit the
+ transmitted bandwidth. When combined with forward
+ error correction and interleaving, this allows us to
+ have a very robust 19.2 kilobit data link with only
+ 10-40 milliwatts of transmit power, a whip antenna in
+ the rocket, and a hand-held Yagi on the ground. We've
+ had flights to above 21k feet AGL with great
+ reception, and calculations suggest we should be good
+ to well over 40k feet AGL with a 5-element yagi on the
+ ground with our 10mW units and over 100k feet AGL with
+ the 40mW devices.
+
+ === APRS
+
+ TeleGPS 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; that
+ process is described in the Configure TeleGPS
+ section of the TeleGPS Application chapter.
+
+ 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.
+
+ 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.
+
+ .TeleGPS 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
+ |1286
+ |Device Serial Number
+ |====
+
+ Here's an example of an APRS comment showing GPS lock with 6
+ satellites in view and a battery at 4.0V from device 1286.
+
+ ....
+ L6 B4.0 1286
+ ....
+
+ Make sure your battery is above 3.8V 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.
+
+ === Configurable Parameters
+
+ Configuring TeleGPS is very
+ simple; the few configurable parameters can all be set
+ using the TeleGPS application over USB. Read
+ the Configure TeleGPS section in the TeleGPS Software chapter below
+ for more information.
+
+ ==== Radio Frequency
+
+ Altus Metrum boards support radio frequencies in the 70cm
+ band. By default, the configuration interface provides a
+ list of 10 “standard” frequencies in 100kHz channels starting at
+ 434.550MHz. However, the firmware supports use of
+ any 50kHz multiple within the 70cm band. At any given
+ launch, we highly recommend coordinating when and by whom each
+ frequency will be used to avoid interference. And of course, both
+ TeleGPS and the receiver must be configured to the same
+ frequency to successfully communicate with each other.
+
+ ==== Callsign
+
+ This sets the callsign used for telemetry and APRS to
+ identify the device.
+
+ ==== Telemetry/RDF/APRS Enable
+
+ You can completely disable the radio, if necessary, leaving
+ TeleGPS only logging data to internal memory.
+
+ ==== APRS Interval
+
+ 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.
+
+ ==== Maximum Flight Log
+
+ Changing this value will set the maximum amount of flight
+ log storage that an individual flight will use. The
+ available storage is divided into as many flights of the
+ specified size as can fit in the available space. You can
+ download and erase individual flight logs. If you fill up
+ the available storage, future flights will not get logged
+ until you erase some of the stored ones.
+
+ ==== Logging Trigger Motion
+
+ If TeleGPS moves less than this distance over a long period
+ of time, it will not log that location, saving storage space.
+
+ ==== Position Reporting Interval
+
+ This sets how often TeleGPS reports position information via
+ telemetry and to the on-board log. Reducing this value will
+ save power and logging memory consumption.
projects / fw / altos / blobdiff