Re: stranded vs. solid wire
Most high speed data signals are a stream of voltage pulses, representing digital 1s and 0s.
The current is very low, so resistance is not too critical.
The propagation time of these high speed voltage pulses is affected more by the capacitance of the cable than any other factor.
(Quote from cable manufacturer's literature)
"Capacitance in cable is usually measured as picofarads per foot (pf/ft). It indicates how much charge the cable can store within itself. If a voltage signal is being transmitted by a twisted pair, the insulation of the individual wires becomes charged by the voltage within the circuit. Since it takes a certain amount of time for the cable to reach its charged level, this slows down and interferes with the signal being transmitted. Digital data pulses are a string of voltage variations that are represented by square waves. A cable with a high capacitance slows down these signals so that they come out of the cable looking more like "saw-teeth", rather than square waves. The lower the capacitance of the cable, the better it performs at higher frequencies.
At low frequencies the impedance is largely a function of the conductor size, but at high frequencies, conductor size, insulation material and insulation thickness all affect the cable's impedance.
Matching the cable impedance to the transmitting and receiving devices is very important. If the system is designed to be 100 Ohms, the cable should match that impedance, otherwise error-producing reflections are created."
Ed
[ October 20, 2003, 12:47 PM: Message edited by: Ed MacLaren ]