Many thanks for the hints Marcus.
I'll make an attempt.
Patrik
----- Original Message -----
From: Marcus D. Leech
To: [email protected]
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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