Survey the air around you and record numbers instead of bars

short · 40 min · Objective 2.1

Task

Produce a channel and signal survey of the wireless networks visible from one location, in dBm, and identify the congestion that any recommendation would have to address.

Steps

  1. From one fixed location, record every visible network into lab/wifi/survey.csv with header ssid_masked,band,channel,width_mhz,signal_dbm,security -- mask the network names as net01, net02 and so on, because neighbours' network names are not yours to publish. Windows' survey, netsh wlan show networks mode=bssid, gives signal only as a PERCENTAGE: convert with dBm = (percent / 2) - 100, the mapping Windows documents (it saturates: anything stronger than -50 dBm reads 100%), and say in the file that you did. On Linux nmcli is a percentage too; iw dev <interface> scan reports dBm directly.
  2. Record your own network's row separately in lab/wifi/mine.csv with the same header, unmasked.
  3. Count the networks per channel in the 2.4 GHz band into lab/wifi/occupancy.csv with header channel,networks,total_dbm.
  4. Write lab/wifi/verdict.md naming which of channels 1, 6 and 11 is least occupied, weighted by signal strength rather than by count, and showing the arithmetic.
  5. Record the same survey from a second location in lab/wifi/second.csv and note in lab/wifi/difference.md which networks changed by more than 10 dBm between the two.

Verify

These checks run in a POSIX shell: Terminal on macOS or Linux, and on Windows Git Bash (it comes with Git for Windows) or WSL. A stock Windows PowerShell or Command Prompt has no awk or grep, so there the first line fails.

awk -F, 'NR>1 && NF>=6 {n++} END {print n" network(s) surveyed"}' lab/wifi/survey.csv
awk -F, 'NR>1 {print $2}' lab/wifi/survey.csv | sort -u | wc -l
awk -F, 'NR>1 && NF>=3 {n++} END {print n" channel(s) counted"}' lab/wifi/occupancy.csv
grep -Eoi 'channel (1|6|11)([^0-9]|$)' lab/wifi/verdict.md | sort -u    # the channel(s) the verdict names
awk -F, 'NR>1 && NF>=6 {n++} END {print n" network(s) at second location"}' lab/wifi/second.csv
grep -c . lab/wifi/difference.md

Three or more networks surveyed, both bands represented where both are in use, channel occupancy counted, a verdict naming one of the three channels, and a second location recorded. If every signal figure is positive, you have recorded bars rather than dBm.

Notes

Mask the network names. A published survey listing neighbours' network names alongside their security modes is a document you would not want written about your own home.

This is an independent study companion for CompTIA A+ Core 1 220-1201 and is not produced by or endorsed by CompTIA.