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xaelsouth / rtl-wmbus

Software defined receiver for wireless M-Bus with RTL-SDR
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Filtering with hardware FIR #16

Closed alalons closed 3 years ago

alalons commented 3 years ago

Hello Xael! Reading about RTL chips there seems to be configurable FIR filters on hardware. Seems to me that would be useful to decrease CPU load.

"...Furthermore, the downsampling is configurable: how far the samplerate is lowered after the low-pass filter, which also determines the simultaneously receivable bandwidth. And part of the low-pass filter turns out to be a FIR filter with programmable coefficients, although this flexibility is not exploited by current driver software"

Just thinking loud

xaelsouth commented 3 years ago

Hello alalons!

Well, rtl_wmbus should be understood as a pipe filter only - it does not include anything hardware specific and is doing just nothing with underlying hardware. This job is done by rtl_sdr (for RTL SDR) or rx_sdr (for LimeSDR Mini and other hardware). Downsampling is not a problem at all because it's implemented as an averaging filter, which is basically a simpler adder. After averaging every n-th sample will be dropped - that's all.

I will close the issue now.