Hi Daniel,
On 24-05-12 11:14, Daniel Ankers wrote: > Does anybody see a reason to add C4FM in this version of the specs? (appart > from "I want everthing"). > > I have no special knowledge here, but I'd say put C4FM in, for two reasons: > 1) The UK licence has the following note: >> The bandwidths of emissions should be such as to ensure the most efficient >> utilisation of >> the spectrum. In general this requires that bandwidths be kept at the lowest >> values which >> technology and the nature of the service permit. > If we can reasonably reduce the bandwidth requirements, we ought to - > or we ought to at least consider it. OK. Fair point, but ... my question remains. Why would you then use 4800 bps / 2400 baud C4FM for that instead of opting for 2400 baud GMSK? Systems like DMR and dPMR use C4FM as they use AMBE+/AMBE+ which has a bitrate that needs more then 2400 bps. We have the luxery of a better codec that can operate at 1400 bps, so -even with FEC- fits into a 2400 bps stream. We do not need to use C4FM to have a digital voice stream in half the bandwidth of 4800 baud GMSK and comply with the regulations. Even more. 2400 baud GMSK has a 3 db S/N advantage over 2400 baud C4FM. So the question remains. Is there a technical reason to incorporate C4FM in the specification? (appart of the "they have it so we must have it too" or "it's new, so it must be better"). Don't get me wrong. I do not have anything against C4FM or 4FSK. And there is nothing that should stop people experimenting with it. I'm just trying to keep the specification as close as possible to the actual "production" modes in use. If experiments do show that C4FM is interesting, it's logical that it should be in there. > Dan MD1CLV 73 Kristoff - ON1ARF ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
