the physical power depends on your waveform. Generally, the power is always
, which, thanks to Ohm's law (
) is 
. As you might know from the basics of electrical engineering, one can represent harmonic functions such as a voltage sine generated by a function generator as complex number with magnitude 
and phase 
, i.e. as 
; notice that for the power consideration, you can omit the 
, it always having the magnitude 1. Use your math basics to find the average power by integrating over a period. For harmonic signals you'll find that if you set 
.2. Moreover, am I supposed to connect the signal generator directly to the TX/RX port?If you can make sure your signal generator doesn't push more than -15dBm into the USRP, then sure. Otherwise, use a calibrated attenuator and adjust your measurement.
I don't know which signal generator you use, but most RF signal generators I know accept both, either voltage/amplitude or power as setting.
Also make sure your signal generator is set to 50Ohm impedance, if that is adjustable.
3. Finally, if that was the case, how do I observe the digital power on the USRP n210?Well, the magnitude of the imaginary and real part of the digital samples are proportional to the voltage on the I and Q input of the ADC... Soooo: Digital power is just I²+Q² = |s|², the magnitude squared.
All in all, these are pretty basic questions; we're constantly working on making GNU Radio more beginner-friendly, but to do that, we might at times need to refer people to adequate literature.
So: May I ask what background you come from?
Best regards,
Marcus
PS: could you also try to keep the discuss-gnuradio@gnu.org mailing list at least in CC:? It's always better to ask the whole list instead of individual people. I might not always have the time...
On 22.03.2016 17:48, Fikrat Al-Kazimi wrote:
Dear Marcus,
Thanks a lot for your reply. I'm really grateful!
I have a few more inquiries I wish to get your help with if you don't mind. I just got access to a function generator and I plan on generating my injected signal using it.
1. The physical power of the injected signal is measured as Vmax^2 / 2R ?
2. Moreover, am I supposed to connect the signal generator directly to the TX/RX port?3. Finally, if that was the case, how do I observe the digital power on the USRP n210?
I apologize for the basic questions, but I'm fairly new to this field.
Best regards,Fikrat
On Tue, Mar 22, 2016 at 12:24 AM, Marcus Müller <marcus.mueller@ettus.com> wrote:
Dear Fikrat,
Feed in a known power, note down the digital power, repeat for another known power.
You'll get three input power->digital power mappings.
Now, assume the power transfer function is a linear one:
With the twomeasurements you can simply deduce the slope
of the above function; simple math, subtract the equations:
and find.
Repeat with a few other known powers to make sure you're in the linear region.
Whatever you do, never feed in more than -15dBm into your device!
Best regards,
Marcus
On 21.03.2016 23:05, Fikrat Al-Kazimi wrote:
Hi guys,
I hope you're all doing well.
I'm been searching a lot and I read that if I want to measure the absolute power ( in W or dBm ) using the usrp_spectrum_sense.py, then I must calibrate the USRP by injecting a signal of known physical power.
Can someone please walk me through the calibration steps? How can I accomplish this and what do I edit in the code after calibration is complete to help me sense the absolute power instead of power_dB?
Thank you for your help!
_______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
_______________________________________________
Discuss-gnuradio mailing list
Discuss-gnuradio@gnu.org
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
No comments:
Post a Comment