I'm always showing my ignorance, but what is cam. I kind of understand psk and bqpsk as my ARD9800 uses bqpsk for the carriers carrying the voice data and sst and ascii keyboarding function of the modem. Sorry to tie up the group with an elementary question that I should know. 73s, Jack wa5rop
----- Original Message ----- From: "KV9U" <[EMAIL PROTECTED]> To: <digitalradio@yahoogroups.com> Sent: Tuesday, January 23, 2007 9:55 AM Subject: Re: [digitalradio] PSK Modes > If I understand it correctly, the raised cosine pulses tend to be more > efficient with power, reduce the crest factor (Pactor 2 is under 1.5), > and perhaps make it easier to have a cleaner signal. > > Just for clarification I have a question: Is QAM modulation a form of > ASK? It would seem so to me but I am not sure. Otherwise, what other > modulation forms fall into the ASK category? > > Although the SSTV modes are not automatically adaptive, there is a > limited choice of number of tones, but for the most part I believe that > they have found 16QAM to be about all you can get to work well on many > HF circuits, particularly on the lower frequencies. > > I wonder how a 4-QAM mode compares to say a 4-PSK mode when up against > the ionosphere? > > There must have been a reason that DRM uses QAM instead of PSK? Any > thoughts on why? > > In terms of coding, it would be very interesting is to compare two > multitone modems, perhaps a 2 tone and an 8 tone (similar to pactor 2 > and 3) and have one with R-S and one with Viterbi and see if there is > any difference on various circuits. > > Does anyone have information on this already? > > 73, > > Rick, KV9U > > > Jose_Angel Amador Fundora wrote: > >>> >>>We know from Pactor 2, that a raised cosine shaped pulse is likely a >>>very good basic waveform. >>> >>> >> >>That is for saving bandwidth, mostly. It might allow better decoding, as >>well. >> >> >>>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. >>> >>> >> >>I don't know if the least complex of it all is ARQ...most likely, the rest >>is harder to implement. >> >>Yes. A key requirement is having the highest distance between >>constellation points to >>have an edge against the noise (or QRM). That's why, in DRM, the FAC uses >>4QAM, as it allows to send the reduced but very important info it conveys. >>But the MSC must use 64QAM, because the amount of data to be sent does not >>allow otherwise in the least bandwidth. >> >> >> >>>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? >>> >>> >> >>Certainly...all those tricks add up, and most likely, in a non >>proportional way...I cannot assure it by heart, but is very likely. One of >>the gains of the code used in pactor modes is >>using convolutional encoding with Viterbi decoding. The Viterbi decoder, >>knowing the history >>of what has been sent, as the convolutionally coded stream depends on what >>has been sent >>previously, makes a soft decode of what is the most likely symbol >>transmitted. RS coding, after deinterleaving, on the other side, may allow >>to recover erors WITHOUT retransmission, which may save more "bandwidth" >>than what is wasted on the FEC overhead. >> >>Also, P2 and P3 avoid the edges of the channel to have the least amplitude >>and delay differences between carriers. That's why a "reduced" version of >>Q15X25 is being more succesful >>in holding the link. >> >> >> >>>73, >>> >>>Rick, KV9U >>> >>> >> >>73, >> >>Jose, CO2JA >> >> >> >> >>______________ ______________ ______________ ______________ >>Correo enviado por ElectroMAIL. Facultad Eléctrica. CUJAE Dominio: >>electrica.cujae.edu.cu >> >> >> >> >> >> >> >> >> > > > > > Announce your digital presence via our DX Cluster > telnet://cluster.dynalias.org > > Our other groups: > > http://groups.yahoo.com/group/dxlist/ > http://groups.yahoo.com/group/themixwgroup > http://groups.yahoo.com/group/contesting > http://groups.yahoo.com/group/wnyar > http://groups.yahoo.com/group/Omnibus97 > > > Yahoo! Groups Links > > >
