Xbee 3 LTE-M signal strength command "DB" range

XBee & XBee Gateway XBee - Cellular
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1

Hi,

I am using an Xbee3 LTE-M/NBIot modem, and currently it is connected and sending fine. However, the response to the “DB” signal strength command is coming back as 45d, which is not in the range of the response in the manual, which lists "0x71 - 0x33 (-113 dBm to -51 dBm) [read-only] ".

I am using the Xbee ANSIC library, and the return from the command response in ->value[] is a U8 and the length is 1, so I assume this is returning as a normal integer and not some sort of hex value. Is the true range of the “DB” response different than 113-51?

Thanks,
Thomas P.

2

Thomas, no, that range is correct. What is the actual Hex value you are getting from the DB command?

3

The exact bytes returned are (api mode) in hex:
88 14 44 42 00 2d b0

This seems like a valid response for DB except that 0x2d is not within the expected range.

4

That is not a valid response. Try sending the following in XCTU without the Library doing it. 7E 00 04 08 01 64 62 30

5

I ran it in XCTU and it returned 7E 00 06 88 01 64 62 00 2D 83

Also in the normal XCTU UI the “DB” row is showing “2D”

6

Actually mvut, the response tpeterson posted IS a valid response, if you prepend the bytes that were left off (7E 00 06).

tpeterson, if you update the XBee 3 Cellular device to the 11416 firmware which was released a few weeks ago, you will find that DB will return -51 (0x33) instead. There was a calculation bug in the firmware which is now resolved.

Additionally I would advise you to use the ATSQ and ATSW commands (Signal Quality and Signal Power) instead of ATDB. This Knowledge Base post explains why RSSI (ATDB) is not a useful measure on LTE.

7

Did you update to 11416, as I mentioned in my previous comment? 11415 and earlier have a bug where the ATDB value that could be reported (which is only an approximate number reported by the cellular component) was not capped at -51. 11416 fixes this.

Also I just noticed I forgot to link the Knowledge Base post I was talking about: https://www.digi.com/support/knowledge-base/4g-lte-rssi-vs-rsrp

8

The firmware version was 11415 so I have updated it, and I will look into the ATSQ and ATSW commands, thanks.