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Harald Welte laforge at osmocom.orgHi Kim, On Sat, Feb 15, 2020 at 09:33:49AM +0100, Kim Mortensen wrote: > From reading books and sites i find that I should probably used a > raised cosine filter to keep the signal form beeing distorted (ISI). > am i correct in my assumption? I'm not the expert on this subject, but RRC filters are used in a lot of receivers for (at least) GMSK or DQPSK, including the osmo-tetra implementation. > and do you have the open source code i can inspect, regardless if programming language. osmoocm-tetra includes a Pi/4 DQPSK demodulator, you can find it in osmo-tetra.git at src/demod/cqpsk.py. It uses the root-raised-cosine filter provided by gnuradio. In general, we would of course appreciate if you could contribute to the osmo-tetra implementation, rather than creating another implementation of something that already works in osmo-tetra. But it's of course your time and your call how you want to spend it :) However, if you have your C# demodulator in a working stage, you could integrate it with the phy/mac implementation of osmo-tetra by generating the same soft-bit input file format that 'tetra-rx' consumes. Regards, Harald -- - Harald Welte <laforge at osmocom.org> http://laforge.gnumonks.org/ ============================================================================ "Privacy in residential applications is a desirable marketing option." (ETSI EN 300 175-7 Ch. A6)