On 28/04/2011 7:38 AM, Patrik Tast wrote:
Hi All,
How do I convert the value from a number sink to dBm?
GRC attempt
http://www.poes-weather.com/~patrik/1.7GHz/HRPT/April-27th-2011/Screenshot-GRC.png
<http://www.poes-weather.com/%7Epatrik/1.7GHz/HRPT/April-27th-2011/Screenshot-GRC.png>
Output
http://www.poes-weather.com/~patrik/1.7GHz/HRPT/April-27th-2011/Screenshot-7.png
<http://www.poes-weather.com/%7Epatrik/1.7GHz/HRPT/April-27th-2011/Screenshot-7.png>
Regards,
Patrik
First, received signal *power* is proportional to the square of the
received *voltage*, and the received *voltage* (instantaneous) is
what comes out of a USRP source block.
I usually feed into a complex-to-mag-squared block, followed by a
single-pole IIR filter, then I decimate it with a keep-one-in-N block to
reduce
the data rate. Now, after this, you have an unscaled estimate of
the signal strength across whatever bandwidth is "seen" by the
complex-to-mag-squared block. If you want to scale it into dBm, then
run it into a log10 block, and set 'n' to 10, and 'k' to whatever
calibration constant you have determined experimentally will map your
power estimates into actual received dBm.
Here's the thing. None of the hardware involved here is
intended/designed to be a precision measuring instrument. So you have
to calibrate
according to your own local setup so that you get dBm numbers that
make sense. Those calibration constants can, and usually will, change
with frequency, since most garden-variety amplifiers, mixers, etc,
aren't perfectly flat across their operating frequency.
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