1. Swarm M138 Modem - Swarm-Technologies/Getting-Started GitHub Wiki

Q: What is the difference between $RT RSSI=<rssi_bkgnd>*xx and $RT RSSI=<rssi_sat>,SNR=<snr>,FDEV=<fdev>,TS=<time>,DI=<sat_id>*xx messages?
A: $RT RSSI=<rssi_bkgnd>*xx messages represent the background noise in the local testing environment as measured by the Modem. These messages can be enabled or disabled by using the $RT command as documented in the Modem’s Product Manual.

The longer $RT messages in the format $RT RSSI=<rssi_sat>,SNR=<snr>,FDEV=<fdev>,TS=<time>,DI=<sat_id>*xx represent satellite beacons that are received by the Modem. These messages are unsolicited and will be presented to the user application as long as the query rate for $RT messages is not 0. The RSSI value provided here represents the amount of signal being received by the Modem. Whereas, the value returned when a satellite signal is not present is the background noise, which while similar, represents the actual noise floor.

Q: What are satellite beacons?
A: As Swarm’s satellites pass over any given location, they will send out beacons to Swarm’s Modems at a rate of 60s, or more frequently. The Modem will attempt to transmit any queued transmission ($TD) messages after receiving a satellite beacon.

The SNR value represented in the longer $RT message is an important data point to monitor for reliable transmissions. The SNR value should ideally be > 0 dB, but the device may also be able to transmit with a SNR down to -6 dB. If the SNR is consistently < -6, then the device may have too much conducted/radiated RF noise. The SNR could also be affected by the ambient device environment since there may be other transceivers in the area that are generating noise in the same frequency bands. The SNR will also be impacted by the characteristics of the satellite pass since a satellite that is lower on the horizon may have a weaker communication signal with the Modem compared to a satellite that is “closer” to the Modem at a higher elevation angle.

Q: What is the default hold time of $TD transmission packets?
A: The default hold time is 48 hours.

Q: How can I change the hold time of $TD transmission packets?
The hold time of $TD transmission packets can be configured by using the $TD command at the time of packet creation using the instructions provided in the $TD - Transmit Data section of the Product Manual.

Q: What is the latest revision of Modem firmware?
A: The latest firmware version for the Swarm M138 Modem is v2.0.3.

Q: Why do I see an “INVALID” message during the Modem bootup sequence?
A: An "INVALID" message during boot-up is normal and expected when there is no firmware update being performed. The message will show "VALID" if there is a firmware update file waiting for installation, but the message shows "INVALID" since there is no firmware update for that Modem.

Q: What is the time zone used by the Modem?
A: The time zone used by the Modem is UTC.