I'd like to hear some discussion from people here on the following question, which has been bothering me for some time.
In the normal POTS ( plain old telephone system ) , in the past it was noted that the frequency response fell off after about 3 khz. It was used only for voice and low speed fax, and any attempts to do more would just roll off and phase distort and was doomed to failure, Now, my dialup can handle 56 Kbaud. This means at least at 26 khz bandwidth with low phase distortion, and probly more, depending on how low the BER needs to be....
So, have the POTS lines been upgraded or was the system capable of doing this all along ???????????
Now, I understand M-ary signalling, data modems, and multiphase encoding.... However, none of that seems to account for a 3khz line suddenly being able to handle a 26khz min bandwidth. I expect to hear several different explanations, and I'm interested in all of them. The gurus of data , and bandwidth, and Fourier series are all asked to give the explanation their own particular spin on this..
Thank a lot , guys...... I am always interested in learning new ways
to account for things that I "thought" I understood....
Andy in Eureka, Texas (retired engineer )