Many thanks for the hints Marcus.
I'll make an attempt.
Patrik
----- Original Message -----
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?
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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