I think that i am a little bit confused with calibration. Is there any
way to determine the gain of the circuitry in front of the ADC? Is it
correct enough to say that power level at the input of PGA in front of
ADC is
just ((sampled_value*Vp-p)/2^12 ^ 2 ) / Rinputpga?
The total gain in front of the ADC will vary from daughtercard to
daughtercard, and with frequency.
Calculate the power inside the flow-graph, which is proportional to
AVG(I*I + Q*Q). For RMS power, there's an RMS block.
What you need to do is use a *calibrated-in-power* signal source, and
use that to calibrate your receiving setup.
You can't reliably backtrack from the values coming out of the USRP,
because you don't know the total gain in front of the ADC to sufficient
precision.
On Mon, Jun 3, 2013 at 5:05 PM, Marcus Leech <[email protected]
<mailto:[email protected]>> wrote:
I'd tune slightly-off the target frequency. The gain isn't going
to change that rapidly across the tuned frequency range. If I
were doing this, I'd probably calibrate every 20Mhz or so.
Since neither UHD nor Gnu Radio have the concept of calibration
data, you can store it in whatever way is appropriate for your
application. It's a simple matter of programming...
on Jun 03, 2013, *Nemanja Savic* <[email protected]
<mailto:[email protected]>> wrote:
Thank you Marcus for super fast answer. Well, for the begining
I would like to skip temperature calibration, only power level
calibration regarding frequency. I have following doubts:
1. To which frequency should be tuned USRP if for example
generator generates 400 MHz. Should it be almost the same
frequency, so that downconverted signal falls very close to DC
or something else.
2. What is the best advice for storing calibration data.
On Mon, Jun 3, 2013 at 4:44 PM, Marcus Leech
<[email protected] <mailto:[email protected]>> wrote:
Indeed, the only way to do this is to use a signal
generator with known power levels, and precision
attenuators. You'll have to repeat the process over the
full tuning range of the device(s) in question, since
effective gain will change a little with tuned
frequency--that's just a natural property of analog RF
components. The gain will also change (a little) with
ambient temperature as well, so it depends on how precise
you want your calibrations to be.
on Jun 03, 2013, *Nemanja Savic* <[email protected]
<mailto:[email protected]>> wrote:
Hi all guys (yet again),
I have a question about calibrating received power
level of my USRP, equipped with wbx, lftx and lfrx.
I am not sure whether it is apropriate to discuss that
here.
Basically I would like to be able to determine
absolute power level I am receiving. I suppose that
basic procedure for doing this would be using super
precise, expensive signal generator. Then tracing
signal of know power to daughter board and measure
power level in fft sink. And maybe also doing this for
complete band of daughterboard usage. If the previous
is correct, than I would like to ask you, how do you
store calibrating data, inside .h file or ...?
Best and thank you,
--
Nemanja Savić
------------------------------------------------------------------------
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--
Nemanja Savić
--
Nemanja Savić
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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