Hello Gayathri, On 25.08.2014 10:17, Gayathri Ramasubramanian wrote: > Hi > Thank you for your note. > My questions here are just based on my previous measurements and your last > mail. kindly clarify the same. > > 1) Is it possible that different USRPN210 devices with WBX boards have the > different calibration factors. I set the channel gain to 0 and still get : > [...] > Your values seem to be different , > Hence the question. Yes, that will be the case, as with any analog circuitry; amplifiers, filters and such are produced with tolerances, and thus these values are expected to change from device to device. > Is this correct or am I doing something wrong. As my values seem to be > almost 30 ~ 33 higher than ones you are getting from your tests. what could > be causing this error/ discrepancy. 30dB *higher*? Are you sure you are inserting the same power (by the way, -40dBm is quite some power and I would generally recommend using an attenuator to avoid damage if the input power rises, as Lou already warned about)? Are integrating over the same number of samples? As a special note to your measurements: You'll sometimes see LO leakage, which can contribute significantly to total power. To avoid that, you could specify a uhd.tune_request(a,b) instead of a simple target frequency. That would allow you to specify a digital tuning offset, which would move the LO out of your measured bandwidth.
Generally, I wonder what you use these values for, afterwards. Because they are only valid for the 250kHz bandwidth as limited by the antialiasing filter in your USRP's FPGA; if you wanted to use this value for higher sample rates, I'd expect there to be a high level of proportionality, but I guess since your doing calibration now, it would make sense to use a filter on the PC where you can control the noise equivalent bandwidth yourself -- especially since I assume you're measuring a single tone, and that would fit in the narrowest of bandpass filters, which would avoid measuring the power of the input tone including your noise floor over your complete sampling rate bandwidth. If you were using a spectrum analyzer, that would actually shift a analog filter through the spectrum and display the energy passing that filter at every frequency, which would give you a display quite different from mag squared for the full 250kHz bandwidth of 1s of input signal samples. Greetings, Marcus _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
