Re: [Discuss-gnuradio] Measuring RSSI on USRPN200

[Marcus D. Leech]

On 22/10/11 10:56 PM, Bonee Soibam wrote:

Hi Marcus ,
Sorry i did not explain to you my set-up , i have two usrpn200's with RX2400 as the daughterboards . i have omnidirectional antennas . Its a line of sight experiment .  i used .benchmark_tx.py -f 2475M -m bpsk --from-file=test.pdf -S 2 -s 50 --tx-amplitude=0.25 -v
and on the receiver side i ran ./uhd_fft.py and ./rx_ascii_art_dft.py  .
the problem i get in uhd_fft.py is that , as i vary  the transmit powers from 0.25 to 0.85 , i am getting -20 dB  constant peak at a fixed distance . logically it should increase as you said but i am getting constant received values .

My suspicion, having not looked at the code, is that the magnitude of the signals arriving at the
  "amp" block in that flow-graph are already sufficiently larger than "1", that you're seeing clipping
  somewhere in the chain.

Please tell me what to do next . i read on your site that , you can measure analog  RSSI measurements using read_aux_adc(side,0) .
Can you explain a little bit on which file it is referring too . looks like the repository has moved too so i am unable to find which app it is referring to .
Eagerly anticipating your reply
Bonee

o

You *could* read the RX-side aux_adc, but it would give you mis-leading results, since the power-detector
  is showing you the power across the entire post-mixer bandwidth.  It really, really is better to calculate
  the RSSI from the incoming data, and since you'd have to modify your application anyway to
  read the aux_adc, you might as well add a couple of blocks to calculate received power properly.

Also, not all cards *have* an RSSI detector available in hardware, so assuming that they do is
  non-portable to other types of cards.

-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org