12 Model Specific Notes

Mark Jessop edytuje tę stronę 2023-09-13 13:57:41 +09:30

Spis treści

• Weathex WxR-301D
• Intermet iMet-1 / iMet-4

This page provides information for specific radiosonde models.

Weathex WxR-301D

These radiosondes are initially supported in auto_rx in version 1.6.3. Weathex WxR-301D sondes use a very widely spaced FSK modulation which causes auto_rx's automatic peak detector to mis-detect the frequency of the radiosonde transmission. This means that auto_rx's usual scan -> detect - > decode approach will not work correctly. Additionally, the wide signal means the usual radiosonde detection step will be unreliable, and so a special 'wideband sonde' mode has been added.

The suggested configuration for those in areas where WxR-301D sondes are in use is to:

• Set the wideband_sondes configuration setting to True. Note that this is a new configuration file setting, so you may need to add it if starting from an old configuration file.
• Put the centre frequency of the launch site's transmit frequency into the always_scan list.

Other notes:

• The telemetry format does not seem to have a sign-bit for latitude. As a result, positions south of the equator are reported as being above the equator.
• There is no support for extraction of satellite lock status, temperature, or humidity data.

Intermet iMet-1 / iMet-4

iMet sondes do not transmit their serial number within their telemetry packets. This makes life somewhat difficult, as we need a unique identifier for the various mapping systems (sondehub.org / APRS / Chasemapper) to be able to distinguish between different radiosondes, and for multiple stations to contribute positions for the same radiosonde.

As a way around this issue, auto_rx generates a unique ID for each received iMet sonde by using:

• The reported time and telemetry sequence number to calculate the power-on time of the sonde;
• and the transmit frequency of the sonde, quantised to the nearest 100 kHz.

These two bits of information are concatenated, and a SHA256 hash is calculated. The last 8 characters of the hash are used for the Sondehub ID, and the last 5 for the APRS callsign. The code that calculates the ID is available here.

Warning - iMet-1 sondes increment their frame counter twice every second, vs once per second for iMet-4 sondes. This needs to be detected and compensated for when calculating the power-on time. Refer here for the algorithm used.