On 04/21/2021 11:03 AM, Mike wrote:
Marcus,
Thank you for your response.
The variation is on the order of 20%, although it changes from run to run.
Power level from the generator is 10 mV through 40 dB of attenuation.
The B200 is set for maximum gain (minimum attenuation) and is using sc8
format with peak=0.1.
Thanks!
That's about 0.8dB variability. Which is a bit more than I would expect
with the way analog RF hardware tends to have
repeatability issues, particularly as you go up in frequency.
What happens if you use 16-bit samples? What happens if you lower the
sig-gen output by a further 10dB?
The AD9361 chip goes through some calibration exercises (for gain and
other things) every time it starts up, and with a strong
(-30dBm at the input is somewhat strong) narrowband signal on the
input, that calibration might get "confused".
I've copied the usrp-users mailing list, where this discussion is
probably more appropriate.
On 4/21/2021 10:42 AM, Marcus D Leech wrote:
What is the magnitude of the inconsistency?
If you replace the signal generator with a 50 ohm terminator and increase the
gain to near maximum, do you still see the inconsistency?
What power level are you injecting from the signal generator.
Sent from my iPhone
On Apr 21, 2021, at 12:27 AM, Mike <[email protected]> wrote:
Hello,
I'm hoping someone can shed some light on an apparent inconsistency
issue I'm seeing with received I/Q amplitude.
I have a B200 directly connected to an arbitrary waveform generator
through an attenuator. The generator is programmed to repeatedly send a
fixed sequence of AM pulses at a set power level. On the host (Ubuntu
20.04, UHD 3.15.0), a C++ program simply gathers samples (48 MSPS, sc8
OTW and CPU) and computes the average amplitude as I^2 + Q^2.
During a run of the host software, the reported amplitudes are
consistent from sequence to sequence.
However, if the host software is stopped and immediately restarted,
without changing the generator, the reported amplitudes are again
consistent but at a different level than the previous invocation.
Is there some internal adjustment or variable setting performed during
USRP creation and setup that would cause the received I/Q sample
amplitudes to vary with each startup?
Thanks!
