--- In [email protected], "Jose A. Amador" <[EMAIL PROTECTED]> wrote: > > jgorman01 wrote: > > > Bonnie, > > > > Your remarks about this person, and I don't know who it is, are not > > very convincing. Your award winning design apparently had to do with > > co-channel interference. This is not the same as on-channel > > interference that increases the total noise level, which is what BPL > > interference is. On-channel interference requires different > > techniques to solve than co-channel interference. > > > > Better receivers (roofing filters, increased IM3 capability, etc.) > > are all answers to co-channel interference, along with higher > > transmitting power. On-channel interference is a whole different > > animal. It doesn't do any good to have a receiver with an MDS of -140 > > dBm, an IM3 @ 2 Khz of 120 dB, and brickwall filtering of 3 kHz when > > the noise floor is -80 dBm due to BPL and the digital signal you want > > to copy is at -120 dBm. The only answer to this is higher transmitter > > power! > > > > Perhaps you can provide some concrete data on how a digital signal or > > digital processing techniques can eliminate the difference in signal > > level (i.e. signal to noise ratio) between what you're trying to > > receive and the noise floor at the receiver's antenna? > > Well, maybe remembering a few things seems to be in order. The SNR you > get with digital is mostly what > you conceive when you design the system, as on baseband it depends on > the quantization noise > of the ADC/codecs. If your digitally modulated signal is above a given > threshold, the results will be > as clean as the baseband quality you defined. You are transmitting > NUMBERS (does NUMERIQUE, > in french, ring the bell ?? ). Telephone speech aimed at som 50 dB SNR, > compact disks aimed at 90+ dB... > > With digital....you either get thru with a PERFECT signal, or NONE at all.
I am not sure what you are saying here. You seem to be confusing audio dynamic range with the RF SNR a radio needs to extract information. In audio the SNR has more to do with the number of bits used to encode amplitude and the sampling rate. Not the same issue when dealing with RF SNR. > > That is already happenning with ATSC, places that formerly had bad > quality reception getting no > signal, and places with fair to good signals, get flawless reception. > > A good example of that is PSTN PCM links. With some 22 db of link SNR > you get about 48 dB of speech SNR. > If the SNR on the link is higher, nothing happens, you are wasting > power. If it is lower than that, the link will be cut. > On radio systems you have to keep a wider safety margin than on wired > systems, generally. Again, I think you are confusing audio and RF SNR. The link SNR describes how well the signal can be extracted while the audio SNR describes the encoding properties of the speech. Granted an RF link where the signal is below the SNR threshold will introduce noise, but this is because of loss of information, not noise in the encoded data. > > On linear systems, the signal to noise ratio depends directly on the > ratios of message to QRM. > > On exponentially modulated signals, you just have to exceed the capture > ratio of the receiver. > > On digital signals, you get a perfect replica of the baseband sampled > signal, after you exceed the threshold. > If the signal strength wanders about the threshold, you will get > intermittent reception. > > I am disregarding the effects of lossy compression, which is the price > we have to pay for using too narrow > channels. > > On RF digital links, there are other tools to dodge QRM. Maybe, finding > notches in the interfering spectrum, > or in the temporal periodicity of the interferer. I truly believe we > have not seen all there is in the tricks box. > A book on DSP can give some further insight. > Think about what your saying here. Amateur radio is going to become a step-child of BPL, looking for notches in the BPL signal to operate in. In addtion, what was recommended was trashing all current radios and moving to wide band capable ones. Are you ready to put all your analog radios in storage, and tell every other ham in the US that they will have to do the same, and fork over multi-thousands of dollars for new, more capable radios all because we are going total digital? > And of course, the RADIO is a link on this chain. And the chain is as > strong as the weakest link, as we all know. > > Digital does things unthinkable on the analog domain. > > I would suggest you to find and take a look at "Communications Systems" > by A. Bruce Carlson, Fourth edition and > refresh a few things. > > Look for: > > http://www.powells.com/biblio?isbn=0070111278 > > or > > http://www.amazon.com/Communication-Systems-Bruce-Carlson/dp/0070111278 > > Or maybe in some library close to you that keeps a copy. > > There are some other authors, like Sklar, Lathi, etc. > > I am quite familiar with Prof. Carlson books since I was an engineering > student, and I > have followed his publications after that. > > > Jim WA0LYK > > Jose, CO2JA > > > > > __________________________________________ > > XIII Convención Científica de Ingeniería y Arquitectura > 28/noviembre al 1/diciembre de 2006 > Cujae, Ciudad de la Habana, Cuba > http://www.cujae.edu.cu/eventos/convencion > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
