In reading the data sheet on the LMS7002, it would seem that the chip supports setting the analog RX bandwidth to 750kHz, however attempting to go narrower than 1.2MHz in GQRX kills the program with an exception that the BW is not supported. Is this just a limitation of the work-in-progress nature of the driver, or am I missing something?
Also, I am confused by the behavior of the decimation option. I would have thought that as you brought in more decimation, the CPU load would go down, but that doesn't seem to happen. If I reduce the actual ADC rate, the CPU load goes down, but selecting a faster ADC rate and decimating to the same rate doesn't seem to reduce the rate.
In short, I would expect that for carrier frequencies above 30MHz, by reducing the analog bandwidth before the ADCs and cranking up the decimation (which I would expect would be done by activating the half-band filters), it should be possible to have a very narrow bandwidth - even before using the FIR filters.