Measuring RSSI - N210 with RFX2400

GNU Radio
1

Hi list!

Is it possible to measure RSSI on RFX2400 with N210 motherboard (UHD
drivers)?
From the archives, it seems that read_rssi() is defined only for
XCVR2450,
and read_aux_adc(side,0) described on
http://gnuradio.org/redmine/wiki/1/UsrpFAQRSSI
cannot be called (or I’m calling it wrong).

Thank you.

Regards,
Kresimir Dabcevic

2

On 06/04/2011 10:52 AM, Kresimir Dabcevic wrote:

Hi list!

Is it possible to measure RSSI on RFX2400 with N210 motherboard (UHD drivers)?
From the archives, it seems that read_rssi() is defined only for XCVR2450,
and read_aux_adc(side,0) described on
http://gnuradio.org/redmine/wiki/1/UsrpFAQRSSI
cannot be called (or I’m calling it wrong).

There is an “rssi” sensor:
http://www.ettus.com/uhd_docs/manual/html/dboards.html#rfx-series

from the uhd api:
usrp->get_rx_sensor(“rssi”)

or in python w/ gr-uhd
usrp.get_dboard_sensor(“rssi”)

-josh

3

On 06/04/2011 01:52 PM, Kresimir Dabcevic wrote:

Thank you.

Regards,
Kresimir Dabcevic

Only a few of the motherboards have an analog RSSI on the analog
receiver chips, and then exposed through one of the low-speed
ADCs.

A better way is to take your signal stream and compute:

  10*LOG10(DECIMATE(SINGLE_POLE_IIR_FILTER(COMPLEX_TO_MAG**2(SIGNAL))))

This is entirely independent of which daughterboard you have present,
and might also be somewhat more accurate, and less prone to
drift.

4

On 06/04/2011 02:04 PM, Josh B. wrote:

There is an “rssi” sensor:
http://www.ettus.com/uhd_docs/manual/html/dboards.html#rfx-series

from the uhd api:
usrp->get_rx_sensor(“rssi”)

or in python w/ gr-uhd
usrp.get_dboard_sensor(“rssi”)

A disadvantage to the get_rx_sensor(“rssi”) approach is that only some
of the daughter-boards have that (analog) function, and also,
the RSSI is generally sensed at the bandwidth of the RF input to the
down-converter chip, rather than at your final pre-demodulation
bandwidth. Which can produce results that vary from mildly annoying
to quite startling or even wildly wrong.

Which is why I always just compute the signal strength from the data
stream at my final bandwidth.

–
Marcus L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

5

On 06/04/2011 08:07 PM, Marcus D. Leech wrote:

and might also be somewhat more accurate, and less prone to
drift.

Thanks for the answers Marcus.

How can I fetch my whole signal stream from RX in order to perform
computations
with it - copying just first N elements that come from usrp source with
gr_head or is there another method?

Regards,
Kresimir Dabcevic

6

On 06/04/2011 03:58 PM, Marcus D. Leech wrote:

In the case of the RFX2400, the RSSI detector output is operating at the
pre-ADC bandwidth, rather than the input RF bandwidth.
But my comment about the results varying from “mildly annoying” to
“wildly wrong” still stand :slight_smile:

–
Marcus L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

7

Regards,
Kresimir Dabcevic

All the calculations I mentioned are standard Gnu Radio “blocks”. You
just plug them into your
signal stream like any other processing block.

8

Josh B. wrote in post #1003140:

On 06/04/2011 10:52 AM, Kresimir Dabcevic wrote:

Hi list!

Is it possible to measure RSSI on RFX2400 with N210 motherboard (UHD drivers)?
From the archives, it seems that read_rssi() is defined only for XCVR2450,
and read_aux_adc(side,0) described on
http://gnuradio.org/redmine/wiki/1/UsrpFAQRSSI
cannot be called (or I’m calling it wrong)

There is an “rssi” sensor:
http://www.ettus.com/uhd_docs/manual/html/dboards.html#rfx-series

from the uhd api:
usrp->get_rx_sensor(“rssi”)

or in python w/ gr-uhd
usrp.get_dboard_sensor(“rssi”)

Hi Josh,
I’m sending signals with benchmark_tx.py by RF1 and receiving with
benchmark_tx.py by RF2.
Could u tell me how to get the value of rssi and print it on the screen?
Regards!
Curtis