|From:||Marcus D. Leech|
|Subject:||Re: [Discuss-gnuradio] Number sink unit to dBm|
|Date:||Thu, 28 Apr 2011 09:41:02 -0400|
|User-agent:||Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:184.108.40.206) Gecko/20110303 Thunderbird/3.1.9|
On 28/04/2011 7:38 AM, Patrik Tast wrote:
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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