Some of us did try Chip modes when Nino first came out with them, but they did not seem to perform as well as existing modes.
I really implore to our treasured programmers to see if they can come up with some modes that can compete with Pactor modes. Especially some ARQ modes that can work on MS OS. We know from Pactor 2, that a raised cosine shaped pulse is likely a very good basic waveform. Then for the most robust mode, a two tone DBPSK modulation is used and as the conditions improve, the modulation changes to DQPSK and then with further improvements to 8-DPSK and even 16-DPSK for maximum throughput when conditions are very good. This is what enables Pactor 2 to send about 700 bits per second at the peak speed and do it in only a 500 Hz wide span. We know this can be done at the higher speeds under good conditions with sound card modes since SCAMP was even faster than P2, although a much wider signal. The problem with SCAMP was that it had no fallback position. Pactor 3 is runs an occupied bandwidth of about 2.4 kHz, but raw speed is over 2700 bps. Instead of 2 tones, P3 uses up to 18, separated by 120 Hz and modulated at 100 baud DBPSK or DQPSK. SCS has some fairly detailed data on Pactor 3 at: http://www.scs-ptc.com/download/PACTOR-III-Protocol.pdf I wish someone could explain why we can not have a sound card mode that is roughly the same as Pactor 2 at least. Even if there was no ARQ at first. And how different is Pactor 3, than what the SSTV hams are using everyday? Aren't they using OFDM with QAM? If you recall what Tom Rink said back in 1995 on the TAPR HF SIG: "As mentioned in the introduction, PACTOR-II uses a two-tone DPSK modulation system. Due to the raised cosine pulse shaping, the maximum required bandwidth is only around 450 Hz at minus 50 dB. ASK, which was also tested in the early stage, provided poorer results in weak conditions compared with a higher DPSK modulation, as different amplitude levels are more difficult to distinguish in noisy channels than more phase levels. Additionally, ASK increases the Crest Factor of the signal. For these reasons, it is not used in the final PACTOR-II protocol. Basic information on these items can also be found in the first part of this series." Although not ASK, doesn't QAM employ amplitude changes as part of the modulation scheme? What happens if you use a multitone DPSK? It seems to a non-engineering person like myself, that a lot of what P2 and P3 are made up of are really a series of PSK100 or PSK200 tones (carriers). Isn't Q15X25 a similar modulation scheme? It even runs at 83.33 baud rather than a minimum of 100 baud such as P2. Why did it not work as well as P modes? Or is it because it has no coding such as Reed-Solomon block coding or Viterbi convolutional coding? 73, Rick, KV9U Jose_Angel Amador Fundora wrote: >Nino: > >I have not had luck with Chip...not a single QSO so far. > >On 40 meters local NVIS test it did not work. > >Maybe the 300 baud chip rate was too fast for it to work. > >Would it be prefarable to use it on a "close to the MUF, single ray link"?? I >would like to try it on the air. > >How has been the actual experience with Chip modes? > >73 de Jose, CO2JA > > > >---------- Original Message ---------------------------------- >From: "Nino Porcino \(IZ8BLY\)" <[EMAIL PROTECTED]> >Reply-To: [email protected] >Date: Mon, 22 Jan 2007 18:18:07 +0100 > > > >>Walt/K5YFW wrote: >> >> >> >>>if you may be receiving 1, 2 and 3 hop signals. How does this affect BPSK >>>and QPSK signals from for example PSK31/63/125? >>> >>> >>the 3 different signals will sum at the receiver, but, having each one a >>different phase, the sum is destructive with the result that they tend to >>cancel. If the paths are stable you notice a drop in the signal strength but >>if paths are unstable (as it is often the case) one signal may win over the >>others and the phase of the PSK decoder will wander back and forth. The >>clock recovery is also problematic because of the unstability of the >>reference. >> >>Among the possible solutions to multipath there is the spread spectrum >>modulation (as in Chip64) where the symbols at the receiver aren't expected >>at a precise timing, but are decoded in a "clockless" manner. In Chip64 >>signal scope you can actually see the signal trace wandering left and rigth >>due to path hopping or see the ghosted trace of the secondary path. >> >>Nino/IZ8BLY >> >> >> >> >> > > > >______________ ______________ ______________ ______________ >Correo enviado por ElectroMAIL. Facultad Eléctrica. CUJAE Dominio: >electrica.cujae.edu.cu > > > > > > > > >
