Since WLAN cards only measure RSSI, and chipset manufacturers use different formulas for converting RSSI to signal strength, I wanted to try a second card as a sanity check. I chose a Linksys WPC54G V3 card, which uses a Broadcom 54G chipset. I once again associated it with the Linksys WRT54G and made my rounds running NetStumbler in a notebook, using the WPC54G as my WLAN card.
Tip: There is a short discussion about RSSI and its conversion here on the MadWiFi wiki. Be sure to download the WildPackets WhitePapers from the "original location links" for even more on this topic.
Figure 5 shows signal strength vs. location for my test locations, this time for the WPC54G card.
Figure 5: Signal Strength vs. Location - Linksys WPC54G card
Table 3 takes the Signal Level readings from Figure 5 and relates them to an equivalent path loss, which is then overlaid on a downlink throughput vs. path loss plot for the card in Figure 6.
|Test Location||Signal Level (dBm)||Delta||Equiv.
Table 3: Linksys WPC54G Signal Levels
The Path Losses and locations don't match up in terms of dB. But they are surprisingly similar in terms of where they land on each plot's curve. Location 1 is, of course, on the flat area at the beginning of the curve, Locations 2 and 3 in the middle near the "waterfall" and Locations 4 and 5 in the low-throughput "tail".
Figure 6: Path Loss vs. Location - Linksys WPC54G card
While by no means perfect, these examples should give you some idea of how to relate path loss to distance or signal coverage in a residential environent. Please note that if your environment has heavy interference from neighboring wireless LANs, your effective range will be significantly reduced.