Hi Jeroen, Pls check that gut feeling abt pulse shaping very carefully - many ideal demods use "integrate and dump" filters - and IIRC Brady obtained some surprisingly good Eb/No versus BER results for the 2400B modem.
Indeed, the pulse shaping filters used on DMR/C4FM and friends seem to be responisble for the drop in performance compared to ideal FSK modems. Adrian - the 2400B modem is designed to deal with the issues you mentioned - i.e. to run on $40 FM HTs. Could use some more characterization I guess. Re one of your questions - the use of "No" (spectral noise density) takes away the issue of "noise bandwidth" - one neat reason for using Eb/No. Cheers, David On 07/07/16 07:08, Jeroen Vreeken wrote: > Hi Adrian, > > On 07/06/2016 09:20 PM, Adrian Musceac wrote: >> I have read your blog posts about the 2400B modem, but I would really >> like to understand more, like what kind of filters do you use for >> pulse shaping and how do they affect performance/bandwidth, how do you >> track the carrier frequency and correct frequency and phase errors. >> This does not seem to be explained anywhere (I know I could just look >> at the code, but reading an explanation seems easier :) ) >> > > I can help you with that one (I was curious as well): The waveform is > just a square manchester encoding. Any filtering will come from the > transceivers. > I have not yet tested it, but my gut feeling says some pulse shaping > (even just a sine table) would probably improve the error rate a bit. > > Regards, > Jeroen > > > ------------------------------------------------------------------------------ > Attend Shape: An AT&T Tech Expo July 15-16. Meet us at AT&T Park in San > Francisco, CA to explore cutting-edge tech and listen to tech luminaries > present their vision of the future. This family event has something for > everyone, including kids. Get more information and register today. > http://sdm.link/attshape > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > ------------------------------------------------------------------------------ Attend Shape: An AT&T Tech Expo July 15-16. Meet us at AT&T Park in San Francisco, CA to explore cutting-edge tech and listen to tech luminaries present their vision of the future. This family event has something for everyone, including kids. Get more information and register today. http://sdm.link/attshape _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
