It looks like the dBm tag isn't supported in Wireshark. Do you have a capture 
file you can send to the list or upload to the wiki?
Avi Berkovich wrote:
First, thanks for the link.
As for the dBm value, it is present in the capture file (stored right 
after the percentage value in the packet header).
 > Date: Tue, 22 Jan 2008 09:34:55 -0800
 > From: gerald@xxxxxxxxxxxxx
 > To: wireshark-users@xxxxxxxxxxxxx
 > Subject: Re: [Wireshark-users] WLAN APC file and RSSI
 >
 > Avi Berkovich wrote:
 > > Hello,
 > >
 > > Wireshark doesn't display the RSSI value in dBm, only in percent.
 > > This happens with APC files captured with Airopeek.
 > >
 > > Is this a limitation?
 >
 > Are you sure the dBm values are present in the capture file? 
According to
 > 
http://www.wildpackets.com/elements/whitepapers/Converting_Signal_Strength.pdf, 
 > WildPackets prefers to use percentage values.
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 > Wireshark-users mailing list
 > Wireshark-users@xxxxxxxxxxxxx
 > http://www.wireshark.org/mailman/listinfo/wireshark-users
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