Is there anyone knows how to check the signal strength of an access point ? I'm building some directional antennas and I would like to test the signal from home, instead of from the graphic tools generally available for the wi-fi cards. A directional antenna can change a lot of its capabilities by just optimizing some components and I would like to "see" the effects of these changes immediately in the same way as on the wi-fi cards. I have a D-Link DWL2100AP and a D-LINK dfe530TX newtork card. Do you know about some software able to do that ?
Netstumbler will report the signal strength and S/N ratio of both ends of the test link. The DWL-2100AP supports SNMP. You'll find the signal strengths somewhere in the MIB tree. If you're going to use such reporting tools, be sure to change the data rate from auto to some fixed speed as the signal strength will vary with the wireless data rate.
Also see: bjs555monitor.vbs
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This probably won't work with your DFE530TX, but is interesting:
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Are you looking to characterize the antenna (pattern, vswr, etc) or do you just want some clue as to the gain increase? If the latter, just setup a reference antenna with a known gain and compare results with your home made antenna.
Yep. I was getting an awful lot of "circular" antenna patterns until I discovered the obvious. However, you're not done yet. I noticed that fixing the connection speed doesn't necessary disable some of the other speed mutilating features. I testing a Dlink DI-624 and found that if I set the speed to 12Mbits/sec OFDM, I should expect that
802.11b compatibility would also be disabled, since it should never connect at 802.11b speeds. Nope. It continues to listen for 802.11b clients that will never be able to connect. I also found that leaving the super-G, turbo, or whatever modes enabled left it also sniffing for those, which will never connect. Therefore, turn OFF all advanced features before trusting the signal strength readings.
As for accuracy, the wireless cards all generate an RSSI (receive signal strength indicator) reading on a scale of 0 to 254. This is converted in either the firmware (for SNMP) or in software to -dBm signal levels. The granularity of the -dBm output largely depends on how much effort the programmists put into the conversion. In most cases, it's just a lookup table with no interpolation. They may offer good resolution for weak signals, where you need it, and use big jumps at high signals, where nobody really cares. Some manufacturers calibrate each table individually while others just use a best guess. There are at least 5 other ways to generate the numbers including "bit distance" calcs.
When testing for proper aiming, I put my laptop "over there", and started WinVNCServer on it. Then I came back to the desktop, started WinnVNCViewer, and used that to view the laptop screen, where the client monitor tool was running. I could adjust the antenna, and see the results. The traffic of the VNC session itself seemed to make good data for the client monitoring tool. The card that I had at that time didn't run NetStumbler.
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