The BNM, which stand for Boot Noise Measurement, initiates a spectral scan at startup.

/
├── etc
│   ├── bnm
│   │   ├── bnm-868.conf                           # The board configuration file.
│   │   │
│   │   └── bnm.conf                               # The global configuration file.
│   │
│   ├── init.d
│   │   └── bnm                                    # The startup script.
│   │
│   └── rc5.d
│       └── S55bnm -> ../init.d/bnm                # The BNM is started whith runlevel 5.
│
├── usr
│   ├── bin
│   │   └── klk_spectral_scan                      # The utility which run the spectral scan.
│   │
│   └── share
│       └── bnm
│           ├── bnm-868.conf                       # The default board configuration files.
│           ├── bnm-915.conf                       # These files define the min and max frequencies
│           ├── bnm-923.conf                       # to scan.
│           │
│           └── klk-loraloc-v1.0.6.kbin            # The needed loraloc firmware.
│
└── var
    ├── backups
    │   └── bnm
    │       ├── bnm.0.tar.gz                       # The backup files. Every output files are included
    │       └── bnm.1.tar.gz                       # in these files. Backup files are rotated by size.
    └── log
        └── bnm
            ├── bnm_slot1_radio1_180219155423.csv  # The last output files. There is one for each slot
            └── bnm_slot1_radio2_180219155423.csv  # and for each radio.

These parameters can be changed by the user in the global configuration file /etc/bnm/bnm.conf. The BNM feature takes some time when the gateway is booting. To avoid Boot Noise Measurement, disable it in this file (Set disable in the field BNM_ENABLE).
The default configuration is the following.

bnm.conf

# BNM is executed at boot.
BNM_ENABLE="enable"
 
# Radio configuration.
STEP_FREQ_MHZ=1
BANDWIDTH_HZ=62500
BITRATE_BPS=600
 
# Number of samples by frequency.
SAMPLES_NB=20
 
# Additional arguments for klk_spectral_scan.
ADDITIONAL_ARGS="-0"
 
# Number of seconds before scans timeout.
TIMEOUT_SEC=90
 
# Backup size in bytes.
BACKUP_SIZE=102400

The start frequency and the stop frequency are defined in the default board configuration file. The board configuration file name changes according to the region.

bnm-868.conf

# Radio configuration.
START_FREQ_MHZ=863
STOP_FREQ_MHZ=873

Starting BNM... done
Starting ifplugd: done
Starting Monit New Monit id: cd60fece54e80cdd45a0dfdca70916b6
 Stored in '/var/lib/monit/.monit.id'
Starting Monit 5.20.0 daemon with http interface at [localhost]:2812
.
Executing network monitoring daemon...
Semtech packet forwarder v2 start: done
Keros (Kerlink OS Distribution) 3.3.3 klk-lpbs-04018B /dev/console
klk-lpbs-04018B login: root

The result of the measurement is available in the /var/log/bnm/ folder.

root@klk-lpbs-04018B:/user/rootfs_rw/var/log/bnm # lldrwxr-xr-x 2 root root 4.0K Feb 20 15:41 
.drwxr-xr-x 3 root root 4.0K Feb 20 15:40 ..-rw-r--r-- 1 root root 317 Feb 20 15:41 
bnm_slot2_radio1_180220154120.csv-rw-r--r-- 1 root root 324 Feb 20 15:41 
bnm_slot2_radio2_180220154120.csv-rw-r--r-- 1 root root 331 Feb 20 15:41 
bnm_slot3_radio1_180220154120.csv-rw-r--r-- 1 root root 352 Feb 20 15:41 
bnm_slot3_radio2_180220154120.csv-rw-r--r-- 1 root root 337 Feb 20 15:41 
bnm_slot4_radio1_180220154120.csv-rw-r--r-- 1 root root 322 Feb 20 15:41 

In this example, three LoRa modules are connected. For each LoRa module the spectral scan is done for the channel 1 and for the channel 2.

bnm_slot2_radio1_180220154120.csv-rw-r--r-- 1 root root 324 Feb 20 15:41

This file is the result of the spectral scan analysis on the LoRa module located in slot 2 and for the radio channel 1.

The default configuration uses frequency steps of 1MHz on a 62500Hz bandwidth.
For each frequency, 20 samples are taken. For 868 MHz gateway, the start frequency is 863 MHz and the stop frequency 873 MHz. Thus 220 samples are measured. Former measurements are backuped in the directory /user/rootfs_rw/var/backups/bnm.

root@klk-lpbs-04018B:/user/rootfs_rw/var/log/bnm # cat bnm_slot2_radio1_180220154120.csv 
863000000,-125,4,-124,15,-123,1
864000000,-115,3,-114,13,-113,4
865000000,-124,3,-123,17
866000000,-124,18,-123,2
867000000,-126,2,-125,7,-124,11
868000000,-126,14,-125,6
869000000,-127,1,-126,12,-125,6,-124,1
870000000,-127,1,-126,14,-125,5
871000000,-126,18,-125,2
872000000,-127,3,-126,17
873000000,-127,8,-126,12
root@klk-lpbs-04018B:/user/rootfs_rw/var/log/bnm #

In the above result 20 measures has been done for 863 MHz frequency. 4 times the result was -125 dBm, 15 times -124 dBm and 1 time -123 dBm.

The number of steps is limited to 255. Mind that the step number must be below that limit. Ajustments are possible by configuring START_FREQ_MHZ, STOP_FREQ_MHZ and STEP_FREQ_MHZ.