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
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