Re: [Discuss-gnuradio] Number sink unit to dBm

Many thanks for the hints Marcus.

I'll make an attempt.

 

Patrik

----- Original Message -----

From: Marcus D. Leech

To: discuss-gnuradio@gnu.org

Sent: Thursday, April 28, 2011 16:41

Subject: Re: [Discuss-gnuradio] Number sink unit to dBm

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

Output http://www.poes-weather.com/~patrik/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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