At 11:40 AM 18/07/99 -0700, you wrote: >Tim Baird wrote: > >> I hope everyone is benefitting by these simple facts.... > > *chuckle* "Simple facts.." You sound like my physics professor. I for > one >am benefitting very much from the discussion. I got hired at my current job >as a software person, but I have a background in hardware so I try and make >it into the NOC every excuse I get (promotability, don't you know). It >always helps if sound like I have a vague idea what I'm talking about. :)
I'll take that as a compliment ;) > > I just made up my first ethernet cables the other day, and learned an >interesting tidbit that I'm sure is beyond elementary to most of you, but >may benefit someone else. What I was told is that the reason Cat 5 cable is >so much more efficient is that each of the 4 pairs of wire is twisted at a >different rate. This helps reduce the possibility of frequency >synchronization for the EM fields the pairs create. Your description (what you were told) here is incorrect....the number of twists in a cable had **NO** effect on the spectral content of the cunducted signal or resulting radiated/induced signal.....to do so would require the conductors to have a nonlinear conduction characteristic which they most assuredly do not (for all practical purposes). The design of the cable is such that adjacent pairs have as little effectively parallel length as possible. Obviously, the currents in the wires share the same axis, so the magnetic coupling is only reduced by the fact that interfering magnetic fields will tend to induce a common mode current in adjacent pairs...particulary since both conductors in the receiving cable pair --on average-- are exposed equally, the idea in "randomizing" the twists is to reduce the capacitive coupling as much as possible. Capacitive coupling is a more localized effect, and thrives when conductors share a common plane in close proximity...this is why capacitors are designed as two metal plates very close together..the electric field between the plates (conductors) is much higher than if they were perpendicular...or not nicely parallel. I hope this clarifies the situation :) To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
