Recently, I found variations ( SSI ) in Tx power signal between two IXP425 based wireless boards running
madwifi -0.9.4 and latest OpenWRT. The tcpdump shows variations in tx power signal per-packet on the
first wireless board. 
Can anybody point me what causes these variations in tx power. ?  and by default ATH_CAP_TPC is
enabled or not for switching per-packet TPC ?
Following is the wifi setup and antenna diversity.
ath0      IEEE 802.11g  ESSID:"OS4_1"  Nickname:""
          Mode:Master  Frequency:2.437 GHz  Access Point: 00:0B:6B:09:2E:66
          Bit Rate:0 kb/s   Tx-Power=19 dBm   Sensitivity=1/1
          Retry:off   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality=56/70  Signal level=-46 dBm  Noise level=-96 dBm
          Rx invalid nwid:566  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0
The antenna  is connected to "aux" of the Mini PCI Atheros card
Is the above setup is correct ?