At any point either before or after a transmission, it might seem useful to check the signal strength of your connection. To do so, you will need to execute the following on your terminal.
/* Check signal strength */ AT+CSQ\r /* Receive response */ +CSQ: <rssi>
The RSSI command returns:
- 0: Equivalent to 0 bars displayed on the ISU signal strength indicator.
- 1: Equivalent to 1 bar displayed on the ISU signal strength indicator.
- 2: Equivalent to 2 bars displayed on the ISU signal strength indicator.
- 3: Equivalent to 3 bars displayed on the ISU signal strength indicator.
- 4: Equivalent to 4 bars displayed on the ISU signal strength indicator.
- 5: Equivalent to 5 bars displayed on the ISU signal strength indicator.
If the AT+CSQ consistently sends back 0 and you you have a partial view of the sky (for example, next to a tall building) it may take a few minutes for the RockBLOCK to acquire a signal. Try testing in a different location that is as unobstructed by trees and/or buildings. If using the RockBLOCK 9603, make sure that if has been correctly configured for the type of antenna you're using (built-in patch antenna or external antenna).
Checking for signal strength before transmitting seems like a good idea, until the following facts are considered:
- Iridium satellites move across the horizon in a matter of minutes.
- Your available horizon will likely not be spanning all the way to 180 degrees but instead may be obstructed by mountains, buildings or trees.
- The +CSQ command takes about 20 seconds to return a result.
During this time, it is very possible that a satellite may have had an unobstructed view of your RockBLOCK, returned a 5 bar signal and then disappeared behind an obstruction or even the horizon itself.
We recommend simply transmitting your data via the +SBDIX command - if a transmission error occurs, you can try again at a later time. Your account will be billed only the credits that pertain to a successful MO/MT transmission.
Updated about 3 years ago