Received signal strength in dBm.

Daniel Faria dbfaria
Tue Jul 6 13:05:50 PDT 2004

Hi there.  Sorry for bringing this up again, but I'm
having a hard
time getting signal strength in dBm for received

My setup: Keith Smith's linuxAP, w/ hostap-0.0.4
(modified by me).

What I have done so far:

- upgraded the STA firmware to 1.5.6;
- updated the hostap driver in LinuxAP to use
dBmAdjust to get the
  value translated to dBm (rxdesc->signal -

It turns out that dBmAdjust = 0x64 (100).  I changed
both the
client's (Cisco 340) and the AP's drivers to print the
received signal
strength in dBm.  I then ran ping from the client to
the AP.  When the AP 
is reporting -51dBm, the card is reporting -37dBm,
with some random 
oscillation around both values.

My card uses txpower=15dBm, which is probably close to
what the prism
card in the AP uses (iwconfig returned no value in the
AP).  The path
loss in both ways should be similar.  So, it seems to
me that dBmAdjust 
should be 115, or something close to that.  I could by
no means find a 
reason for this +-15dB difference I'm getting.

Any hints?  ANY help will be greatly appreciated.


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