[Discuss-gnuradio] how to retrieve the baseband signal strengh

Hi all I use xlating filter to retrieve the baseband signal and I use such way the compute the samples
signal strengh like this: a = sqrt(i * i + q * q)  (i and q means the complex signal's real part and image part)
then compute the average signal strengh: rssi = (sum of all sample strengh) / (sample count). With this way
all the channel's rssi result are the same(very close consider the same) but actually they are not the same.
Is there any wrong in my method? I do not need the actual rssi value but just need a way to distinguish the
channels' signal strengh.