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. 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. 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. 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/
