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diff --git a/doc/telegps-system-operation.inc b/doc/telegps-system-operation.inc new file mode 100644 index 00000000..e8790db8 --- /dev/null +++ b/doc/telegps-system-operation.inc @@ -0,0 +1,149 @@ +[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. |