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.