agreed. the only way these DMR/ C4FM mod schemes fit into a channel is because they are aggressively filtered...
On 7/07/2016 10:55 AM, David Rowe wrote: > 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 >> Freetel-codec2@lists.sourceforge.net >> 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 > Freetel-codec2@lists.sourceforge.net > 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 Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
