This simulation: https://github.com/drowe67/codec2/blob/master/octave/fsk.m
Was used to compare non-coherent 2FSK to a AFSK over FM, it includes an analog FM modem simulation fm.m (equivalent of a VCO/discrimator). The fm.m module has optional voice band filters. mancyfsk.m is similar, but with manchester encoder baseband signal, which I think is similar to what is being used in this work. Reason I mention this is that the best way to compare the effect of any signal processing step (like a scrambler) is to measure the bit error rate. Cheers, David On 8/4/20 7:12 am, Jeroen Vreeken wrote: > Indeed, I use the packet port of my ft-817, so the signal goes almost > directly to the oscilator and almost directly from the discriminator. > It might also work over the audio ports as the bandwidth might fit if > the filters are not to tight. > But then you would have to compensate for the pre/de-emphasis. I haven't > tried that yet. > > The bit stuffing is indeed to make sure we don't go near DC, and to make > sure there are enough 'flips' to recover the bit timing. > The scrambler looks nice, but we would have to find a balance between > lots of zeroes (easy to sync) and a perfect spectrum. > I'll try some variants on the air soon. > Also note that the frames generated with the test program are not > varying much, a stream with real-world data might look different. But > the pictures you showed both don't look that bad... > > > On 04/07/2020 11:24 PM, Steve wrote: >> I believe it is just direct FSK of the FM oscillator. +/- some >> deviation. Using the data port of most modern VHF radios. >> So on receive you just slice the ratio detector (discriminator output). >> >> The bit-stuffing keeps from long runs of a high or low. My experiment >> is to replace bit stuffing with a scrambler, but I haven't found all >> the places to remove the bit-stuffing :-) >> >> On Tue, Apr 7, 2020 at 4:08 PM David Rowe <[email protected] >> <mailto:[email protected]>> wrote: >> >> Hi Steve, >> >> >From what I understand (please feel free to correct me Jeroen) >> this is a >> baseband PAM waveform over analog FM. I'm haven't seen any >> theoretical >> analysis of these schemes, but we did measure some a few years back: >> >> http://www.rowetel.com/wordpress/?p=4663 >> >> Cheers, >> David >> >> On 7/4/20 5:58 pm, Steve wrote: >> > What would be expected here? Say about 9.5 dB Eb/N0 at 10E-5? I >> think >> > that's what the G3RUH modem got. >> > >> > It will definitely fill up the channel! :-) >> > >> > On Tue, Apr 7, 2020 at 2:43 AM David Rowe <[email protected] >> <mailto:[email protected]> >> > <mailto:[email protected] <mailto:[email protected]>>> wrote: >> > >> > Steve and Jeroen - it would be interesting to measure the >> modem BER (or >> > Packet Error Rate) performance. Steve - we could use >> cohpsk_ch to >> > inject measured amounts of noise. >> > >> > Cheers, >> > David >> >> >> >> >> >> _______________________________________________ >> Freetel-codec2 mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
