https://nuand.com/forums/viewtopic.php?f=9&t=3497
https://nuand.com/forums/viewtopic.php?f=4&t=3802
I modified the flowgraph that jynk posted and I've already solved a few of my problems. I'm running the latest development versions of GNURadio (3.7.10), gr-osmosdr, and bladeRF-cli, all compiled from source. I've done the automatic DC/IQ calibrations. I've attached the two flowgraphs I'm using: one closely based on jynk's original WX GUI graph, and another with additional blocks based on the GNURadio PSK Recovery tutorial that uses QT GUI.
Code: Select all
bladeRF-cli version: 1.3.1-git-35802e3
libbladeRF version: 1.5.1-git-35802e3
Firmware version: 1.9.0
FPGA version: 0.5.0
My current testing is for BPSK signals in a 50kHz bandwidth. I know (now) that the bladeRF's minimum bandwidth is 1.5MHz, and adjusted my sample rates and samples/symbol up accordingly. I've also been using gr_filter_design to help get the pulse shape roughly within 50kHz (why? explained below).
Here are my outstanding issues/questions:
1. I understand that since I'm using the RF_LNA1 loopback mode the received samples != tx samples. However, the power is dropping from -10dB to -50dB, and the constellation is either a unit circle or only around ONE of the two constellation points. Is this normal? What are the best ways to correct these two problems, given my setup?
2. Why is the received signal so "peaky"? There is no flat "passband" shape like the transmitted signal at all.
3. Are there other methods for narrowing my pulse shape (on the Tx side) to get it closer to 50kHz bandwidth besides constantly fiddling with the sample rate/symbol rate/roll-off factor?
Why 50kHz:
I'm building a frequency-hopping spread spectrum system. The intention is to use 25MHz of total bandwidth with 500 x 50kHz sub-channels. A little bit of spillover/noise is tolerable but I don't want the signals bleeding across 2-3 adjacent channels if I can avoid it. Then I'll use a variety of DSP blocks to filter out the 25MHz bandwidth and downsample just the particular 50kHz channel that I'm interested in during a particular hop...
Thanks for any assistance.