The 8FSK125 mode is quite an old mode now and from what I have been reading, commercial/government will eventually move away from that particular waveform in order to standardize on the other newer designs. Because it has one tone that frequency shifts to 8 locations at the rate of 125 baud so it has 3 bits per baud or 375 raw bps rate. Actual throughput is much lower due to repetition of three times when calling. Compared with most other modes we hams use, I do not view 8FSK125 as an optimum mode for signaling purposes since it is not very robust, can not work very much below zero dB S/N, and is extremely wide. But the reason that it is wide, is due to its commercial/government origins in channelized operations where you have a specific channel width available so they designed a waveform to fill the channel.
Pactor 3 is another commercial mode that was specifically designed to use the full width of a typical SSB transceiver bandwidth. The maximum raw throughput is 3600 bps since it has 18 tones running DQPSK at 100 baud for each tone, spaced 120 Hz apart. Thus 18 tones x 100 baud x 2 bits per baud for quad psk = 3600 raw bps. The actual maximum is 2722 bps due to control overhead, but then they use compression so that plain text typically can go through at speeds just exceeding 5000 bps. You would have to ask the Pactor 3 users just how often it actually runs at Level 6, the fastest speed, but I would expect a very stable ionosphere with at least +10 dB S/N or more. Not easy to do this, even with base stations and modest antennas and 100 watt rigs. Pactor 3 drops off tones as needed to match conditions and at Level 4 drops to 14 tones but still with 4PSK. At level 3 it stays with 14 tones but then drops to 2PSK but always with 100 baud. Then at Level 2 it drops to 6 tones and at Level 1 only 2 tones, similar to Pactor 2, but with much wider tone spacing which gives it somewhat more robustness according to the manufacturer. At the slowest speed, it is only running 2 tones x 100 baud x 1 bit per baud = 200 bps. So, at the slower speeds there is nothing all that different from DBPSK100 except it has two tones. The overhead control bits take a large percentage of the throughput so that the Net Data Rate is only ~ 77 bps at the slowest (most robust) speed. As you can see, if hams were able to develop a program that can use several levels of multiple PSK ARQ tones to meet the different conditions and operate reasonably fast in poor conditions and very fast in good conditions, we would have a mode comparable to Pactor 3. 73, Rick, KV9U Demetre SV1UY wrote: > > But isn't 375 bps too little for 2khz width? Pactor 3 does 5200 bps > for 2.4 khz width and 1200 bps for 0.5 khz width. > > I think that if PACTOR 3 can do it, there has to be a way for ARQ-FAE > to do a bit better than 375 bps. > > OF course I'm no expert but 375 bps? Unless there is some > misunderstanding somewhere. But 2 Khz for 375 bps is a wast of > bandwidth I think. > > 73 de Demetre SV1UY > > > > Announce your digital presence via our Interactive Sked Page at > http://www.obriensweb.com/drsked/drsked.php > > Yahoo! Groups Links > > > > > > >
