[Discuss-gnuradio] received signal strength circuit

[Ben Olsen]

Hi,

I'm analyzing transmission between two Ettus USRP boards using the
benchmark_gmsk_tx and _rx.py scripts and I have a question regarding
the rssi (received signal strength indicator) circuits, because i've
noticed some strange behavior.  Let's say I transmit at a center
frequency of 2440 Mhz, with a bitrate of 1Mb/s.  On the wireless
spectral analyzer, I see a spike of appropriate width centered at 2440
MHz, but at the receiver when i use the u.read_aux_adc function to see
the received signal strength from the USRP it gives me a value of
>4000 within 10-20 MHz of the center frequency!  I have the
boards about 3 meters apart.  My questions are:

First, generally, how are the rssi values measured?

Second, is it possible that the antennas that I'm using have a gain
that is too large?  One possible explanation may be that the
antennas transmit at unreasonably high power, saturating the rssi
circuits at the receiver for a large bandwidth.  However, the
spectral analyzer doesn't seem to corroborate this, since the spike it
sees does not seem to be enormous in amplitude compared to the bubbling
sea of noise that surrounds it.  

It boggles me that I can see the 1Mb/s transmission still 10MHz away
from the center frequency at the receiver - is there something I'm
missing?

Thanks very much.