Hi Voitech, many thanks for the hint! I guess i have to learn more about Throb and ThrobX Particular about the "single exception" an why it was implemented.
BR Norbert --- In digitalradio@yahoogroups.com, "Vojtech Bubnik" <bubn...@...> wrote: > > Hi Norbert. > > I do not want to discourage you from your experiments, but I would > like to point out, that there are already two tone chat modes designed > for amateur use on HF, namely Throb and ThrobX. DTMF as well as ThrobX > encode each single character into two simultaneous tones. Throb has a > single exception, idle character is encoded as single tone. DTMF does > not shape amplitude, Throb/ThrobX does. DTMF is much wider than Throb > or ThrobX. > > I believe DTMF was designed for cheap inexact tone decoders and not > fully harmonic encoders and transmission paths, the tones are picked > so their third intermix product is not exactly aligned with other DTMF > tones. If used on HF, one does not want the IMD product fall outside > of the useful signal. On telephone line it does not matter and some > nonlinearity may be even useful to boost SNR. > > On HF I don't believe big tone spacing will bring much benefit when > compared with ThrobX. > > 73, Vojtech OK1IAK >
