RX IQ bandwith

[fei666888]

I would like to know what is the maximum receive bandwidth that can be obtained through the IQ data output. Is it only 12k? I want to get a wider waterfall chart. Is it possible?

[tejeez]

EFR32 can do a much higher receive bandwidth but it will result in a higher sample rate for the I/Q stream.

If sample rate is increased, more processing power will be needed to handle the I/Q data. The 38.4 MHz Cortex-M4F processor core is not that fast after all. In the current firmware, there is some spare processor time left but not a lot. It might be possible to make it a bit wider if needed. Everything in the firmware, however, is pretty much hard coded for the 48 kHz sample rate, so you might need several changes around the code to make everything work correctly.

EFR32 seems to have some digital filtering in hardware for the I/Q stream, limiting bandwidth to about 1/4 of the sample rate, so basically the I/Q stream is oversampled by a factor of around 4. The firmware directly uses this as a channel filter for AM and FM modes, so increasing the channel bandwidth would also affect the received channel bandwidth for AM and FM modes. If you want a wider waterfall display without increasing demodulator bandwidth, some additional filtering could be added in software. That will further increase the processor time needed for signal processing. It would not necessarily be a problem, though, since the SSB demodulator already performs channel filtering in software.

Bandwidth and sample rate are determined by the radio configuration data generated in Simplicity Studio. When I generated the configuration data, I adjusted the configured channel bandwidth by trial and error until it resulted in a configuration with a 48 kHz sample rate (as shown in the radio configurator log file). Since details of the radio peripheral and configuration data are not really publicly documented, I do not really know if it would be possible to reduce the oversampling factor so that bandwidth could be increased without increasing sample rate that much.