APRS Digipeatersoftware DIGI_NED
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Satellite tracking

DIGI_NED has a service build in for tracking satellites. When this service is available on a DIGI_NED digipeater it it advised to promote the feature in in a beacon with you position as a comment or ais a status.

The objective of the Satellite Tracking module in DIGI_NED is to give APRS users a tool to track satellites on APRS without having to invest time and/or money in satellite tracking software. APRS users can use their APRS client software to obtain satellite-tracking information. The only requirement on the client side is that the APRS client must be able to send APRS messages.

General The tracking module has three main functions. These are,

  • Satellite Inquiry,
  • Satellite Tracking

Satellite Inquiry.

An APRS user can inquire DIGI_NED for information about a particular satellite by sending a message query to DIGI_NED. The satellite-tracking module in DIGI_NED uses the 4 position Amsat designator to specify satellites (i.e. Sunsat is so35). Such a query could look like:

  • sat ao40

Upon reception of this message, DIGI_NED will send back a message informing the user whether or not the satellite is in range, and an object containing information about the satellite. This object will be displayed by the APRS client software on a map. The status text of the object will contain AOS (Acquisition Of Signal) information if the satellite is not in range. For example:

AOS@2-3 12:00 LOC

This means that the next pass will be as 12 noon on February third, local time. The time can also be indicated in UTC, and is configurable by the digi owner. If the satellite is in range, the status text will contain information necessary to track the satellite. For example:

U145.823 7D435.398 1 E71 A123 MB

This status text informs the user of the doppler-corrected uplink and downlink frequencies (U145.823 D435.398), the elevation angle (E71), the azimuth (A123) and in which mode the satellite is operating (MB, Mode B). The extra 7 and 1 in the status text are for display purposes only on a Kenwood TH-D7A(G)/E. This allows for display of elevation and azimuth together on the first screen of the object information display on this particular radio. In case the satellite does not exist or if the query is not correctly formulated, DIGI_NED will send an appropriate error message back to the APRS user.

Satellite Tracking Tracking is actually very similar to Satellite Inquiry. An example of a tracking query is:

  • trk ao40

The main difference between inquiry and tracking is that after sending the initial in range/out of range message and initial object, DIGI_NED will be put in tracking mode. This means that DIGI_NED will continuously transmit objects with updated satellite information up to a maximum allowed time set by the digi owner. The interval between the transmission of objects depends on whether or not the satellite is in range. If the satellite is out of range, an object is only transmitted every 15 minutes.

As soon as the satellite comes in range DIGI_NED will transmit a new object every minute. When the satellite disappears below the horizon again, DIGI_NED will resume transmitting objects at the long interval.

These intervals can be configured by the digi owner. The information in the status text of the object changes dynamically also. While the satellite is out of range it will contain AOS information, and tracking information when the satellite is in range.

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