El 06/03/2010 4:49, [email protected] escribió: > I thought, that there has to be a direct specific connection > between the transmitter and the receiver on how to retrieve > the "info" from the spread spectrum. ( SS for dummies ) > > This makes it useful for the militairy, for who it was > originally designed and in the case of cell phones, for > instance, the code recovery algorithm is programmmed in > the system, not secret, I assume, but still hard to figure. > I thought cell phones run over 1,5 Mhz wide spreading. > > Is this true? I for one have never thought or learned > much about SS. ( 75 yrs and retired and I am sure some > will say you know what ) > > 3000 Hz info band -> 1.5 10 e+6,Hz ? > > Anyway what is so frustrating to me here, is that I do not > see a straight definition of SS written in a published book > that I can cross reference. >
Carlson, Bruce, Communications Systems, Chapter 15 Spread Spectrum Systems, p 671, Mc Graw Hill 2002 > I have the ARRL SS source book, and there, all I can find is > that SS spreads the "info band" width between 10 and 100 times. > > Also I thought if one looks with a Spectrum Analyzer,( I have > never done that, ) to a SS signal, is is hard to see the side bands. > Signals so weak and so random, perhaps semi- that one can > have a large number of those side bands from different transmitters > overlapping without causing problems in the communication > process. > It should be that way. But ROS has insignificant spreading when compared to what has become publicly known about SS (i.e., 802.11). > Just a INCREASED noise level, that would seriously be a problem > for EME, for instance, it would cover up the natural background > or with other words, increase the noise temperature, > > Now here you have a few simple concepts, it is crazy talk > yes or no? Please feel free to tell your views with a > basis, where I can look it up myself. > I asked before for a peer reviewed paper "SS for laypersons > or dummies" > > I do only WSJT on HF and on EME as group member, please someone explain > to me why WSJT is, what? JT65A is MFSK with a heavy block coding scheme and high redundancy. It is NOT spread spectrum. > It appears to be legal? > Yes, it is NOT SS and occupies some 170 Hz. It is WELL DOCUMENTED by Dr. Joseph Taylor, K1JT, a Nobel Prize Laureate and Princeton Professor. > What is the difference between JT65C and ROS when it relates > to the SPREAD Spectrum properties, > Apples and oranges. ROS does not quite reach the level of sophistication of WSJT, within the bounds allowed to hams in the US. > WSJT has a smart and efficient info packing scheme that makes > it pretty much an all or nothing system. ROS, produces > a lot of errors, if the signal strenght goes down after > the start, but that is not a SS issue, > Certainly not. ROS is a baby compared to JT65 robustness. > Please explain to me and perhaps quite a few others what > SS is, other than that is "Wide" Im my own mind the width > has not really too much to do with it? True or false. > Ideally, SS should be of infinite bandwidth, which is not viable in practice. As you reduce it to a practical, allowable level, its "magic properties" lose strenght, be it direct sequence or frequency hopping. Theoretically, FH should have a very small dwell time, but then again, to contain at least 90% of the spread message sidebands in a 3 kHz bandwidth makes it "not undescernible from noise". > All straight layman's questions, so who answers them, most of us > like to learn and understand a little. > > 73 Rein W6SZ > 73, Jose, CO2JA
