Steve Underwood wrote:> mk wrote:...>> I know how to generate DC free codes but I don't think you paid enough >> attention to my post. The system definition is what it's and it's as >> close to cast in stone as it can get and it can't be changed. > > > I don't think you paid enough attention in physics lessons. :-) You can > set the design in stone as much as you like. Making it work properly is > another matter. Many, many, systems over the years have been anywhere > from a little quirky to totally unusable because they required DC > response of a channel that doesn't offer it.At least one system failed because all it could pass was approximately DC. The first transatlantic telegraph cable had a frequency response of 1/N Hz, where N was not a very small number. The first commercially successful cable pushed the speed up to two words per minute. They could signal no faster no matter what the spec (or board of directors) said. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
low frequency response of adaptive equalizer?
Started by ●April 21, 2006
Reply by ●April 23, 20062006-04-23
Reply by ●April 23, 20062006-04-23
On Sun, 23 Apr 2006 17:17:22 +0800, Steve Underwood <steveu@dis.org> wrote:>Many, many, systems over the years have been anywhere >from a little quirky to totally unusable because they required DC >response of a channel that doesn't offer it.I seem to be dealing with one of them, one cast in stone by those people who need to be in an instution instead of an institute of the triple something letter ;-)
Reply by ●April 28, 20062006-04-28
>Hi, >I have an LMS based adaptive equalizer which mostly works well but it >doesn't tolerate low frequency inputs too well. The channel consists >of two transformers (high pass) and cable (low pass) and when there is >long periods of no-change in data (which is possible unfortunately >even though the data is scrambled) and the SNR goes down during these >long periods of no change. I think this is because the equalizer's >bandwidth is not high enough ie it is not able to compensate for the >high pass behavior of the transformers. Any idea how to approach this >problem ? >Something I have run into in the past is line transformers that have nonlinearitities at low frequencies. For example, if the transformers high pass cutoff is 3kHz, it could have a nonlinear response below that frequency. If you are transmitting signal energy below 3kHz, you can generate a noise floor due to non-linearities above 3 kHz. In a past application, we prefiltered the signal before transmission through the transformer to avoid raising the noise floor. It may be tempting to say "that region will be filtered out by the transformer anyway", and this is true, but it will raise your noise floor outside that band in the process and afterwards it too late to do anything about it.
