lunes, 8 de abril de 2013

Telemetria CubeBug-1

Telemetry

El Cubebug, transmitirá una baliza en 437.445 Mhz, en AX25 a 1200 bd AFSK FM con el dispositivo de radio AstroDev Lithium Li-1 con un apotencia de aproximadamente 1w. El periodo de repticion de la baliza, puede variar entre 10 y 30 segundos, dependiendo del modo del satelite.
El paquete de AX25 esta encabezado con "CUBEB" y destino "UI"
Tiene 2 formatos de baliza, los paquetes comenzando con "FF FF FF F0" indican una baliza completa y los paquetes comenzando con "FF FF FF F3" indican una baliza corta y una diferente codificación.
La mayoria de los valores requieren una conversión mostradas en la siguiente tabla.

The Capitán Beto (AKA CubeBug-1) will be transmitting a periodic beacon at 437.445 MHz. It’s AX.25, 1200 bps, AFSK (FM), modulated with an AstroDev Lithium Li-1 radio device, transmitting at 1W (aprox). Depending on the current mode of the satellite the beacons will be transmitted every 10 to 30 seconds.
The source of the AX.25 packet is labeled as “CUBEB” and destination “UI”. The data portion contains a binary blob. There are mainly two beacon formats.
Packets starting with FF FF F0 are the complete beacon, packets starting with FF FF F3 are a short beacon, with basic information, and a different encoding.
All numbers in the packets are stored in network byte ordering (Big Endinan). Most values require a conversion formula, provided in the next table.
La baliza corta esta codificada un poco diferente.
 
The short beacon is encoded a bit different. For every bit the satellite wants to transmit it actually transmits 4. So, for example, the 8 bits 0xA5 become F0F00F0F in the air (a nibble per bit). As this encoding transmits more energy with each bit, it will give us a chance to decode some basic telemetry in a worse scenario. The first three bytes (FF FF F3) identify the packet as a short telemetry beacon, the rest must be “decoded” before interpretation.
Capitán Beto Short Telemetry

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