# How wireshark calculate the dbm of wireless signal?

 0 Please, I want to know how wireshark calculate the SSI signal of the wireless network. According to the capture result, the "SSI Signal" is -70 dBm, but the displayed hexadecimal value is "ba". Convert the "ba" to decimal = 186 and not -70. So, I really want to know how wireshark calculate that, because my final year project is about 802.11 capturing. asked 11 Nov '10, 17:51 cshong87 1●1●1●1 accept rate: 0%

 0 Ick - math. Ok... you are right - 0xba converts to decimal 186, but Wireshark displays -70. Short answer = subtract the actual decimal number in that field from 256 and then make it a negative number (e.g., 256-186 = 70 which you make -70). Believe it's done in two's complement math - see the example at http://en.wikipedia.org/wiki/Twos_complement. answered 11 Nov '10, 19:25 lchappell ♦ 1.2k●2●7●30 accept rate: 8% FYI, I was looking at the Radiotap header applied by an AirPcap adapter. (15 Nov '10, 09:35) lchappell ♦
 0 AFAIK Wireshark does not really calculate the signal strength, it only displays what is being delivered from the "driver". Signal Values from my experience are strongly depended on the type of wireless NIC plus the monitoring driver and it's headers. I have lots of captures with negative values and ALSO lots of captures from other cards with a positive value... If you capture directly with wireshark/tshark you should be given the PRISM header information. If your tracefile comes from another software there might be other headers indicating physical properties of the wireless network. answered 15 Nov '10, 02:52 Landi 2.3k●5●14●42 accept rate: 28%
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question asked: 11 Nov '10, 17:51

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last updated: 15 Nov '10, 09:35

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