I’m trying a simple test to create a sinewave output from a WFM modulator block. If there is no audio input, its WFM modulated signal should be a simple sinewave. If I test this with SDRAngel, I see a clean-ish actual sinewave in time domain on the oscilloscope. But if I try to do the same with gnuradio, it seems to produce a glitchy signal.
Could I have any advice on what I might be doing wrong?
Is it a question of “tx calibration” ? or calibration in general? or something else.
See this envelope of the sine captured in the oscilloscope. note the time base in the screenshot. If I zoom into the timebase, then I see the glitchy sinewave behavior.
I investigated some more, and the waveform above seems to happen with the Rational Resampler before the WBFM block. When it is after the WBFM block, this abrupt envelope is not there, but the signal is still quite noisy.
So, I tried the following approach.
Limesuite allows me to read the settings on the device.
So I run SDRAngel, followed by Limesuite to take a dump of the settings - https://termbin.com/k8ye
Next, I load the SDRAngel settings onto the board via limesuite and observe debug messages - https://termbin.com/gb0c
Then, I load the gnuradio settings onto the board and observe debug messages - https://termbin.com/nr2n
Both the debug logs too are attached. My knowledge in this is very limited, but in the case of SDRAngel-settings, the log ends like this.
DEBUG: Selected: VCOL
DEBUG: csw 169; interval [166, 172]
DEBUG: M=195, N=3, Fvco=1300.000 MHz
in the case of gnuradio, log ends like this
DEBUG: Selected: VCOM
DEBUG: csw 174; interval [171, 177]
I only tried the FM transmitter example, and was facing issues. Also, perhaps because of gnuradio, most/all the examples were failing due to a selector block, but that’s easy to get around and get the examples to work.
I can try the other examples once I get back to my radio in 2-3 days’ time.
Also, I’ll let you know the gateware version flashed as well in 2-3 days, but I do remember doing a Limeutil -update as once I initially used Limesuitegui, it had complained of an old gateware version.
My next course of action (since my knowledge of limesdr settings is very limited at this point) was to use the .ini file (settings) that sdrangel uses, and load that using the advanced settings in the limesdr-sink gnuradio-companion block.
One can clearly see that they dont look good in quality compared with the signal generated by sdrangel. So I’m guessing it is some problem with the settings gr-limesdr uses.
I tried two more approaches. Instead of gr-limesdr, I used the soapysdr sink block and the osmosdr sink block with the right settings (antenna=BAND1, “soapy=0,driver=lime”), but face the same issue.
At this point, I’d say there is something buggy somewhere in the gnuradio/limesdr implementations in terms of proper settings.
I would love to help out with this, as generating a simple clean sine wave (fm modulated) seems to be step one in getting things to work.
@Zack, I tried the fm transmit example, and after fixing some issue with the selector, it gave the same problem while trying to create a fm transmit signal.