On Mon, 30 Aug 2010 10:14:14 +0100, David Woolley (E.L) wrote: >That's another of Jim's suggestions that the UK amateur radio trade >and RSGB shop have failed to take note of.
I don't want to take credit for repeating fundamental principles that have been well understood for at least a century. The great telephone companies began using twisted pairs for both short and long lines early in the 20th century. In the early days, the only source of interference was 60 Hz power, so wires were run as parallel conductors, with the twist in the form of a crossover every other pole. This worked fine, because it was much much shorter than the wavelength of the 60 Hz power, and telephone lines were able to run directly under power lines without interference! Today, CAT5/6/7 cable rejects noise SOLELY by virtue of its high quality twisted pair construction. Crosstalk is further reduced by the fact that the pairs are twisted at different rates. These fundamental principles are WELL understood in the EMC world, and those of us working in EMC in pro audio have had to learn them to keep hum, buzz, and RFI out of our systems. I find it ironic that RF folks look down on audio engineering, because "it's only 20-20,000 Hz." In fact, audio systems are far more complex than RF systems -- they span 3 decades of frequency, require transducers that can produce high power over this wide frequency range with controlled dispersion far more complex than most antenna systems, must work in an acoustic environment that is at least as complex as the ionosphere, have dynamic range requirements of 100 dB or more, and must regularly achieve that with signal levels in the millivolt range in an environment that is full of all sorts of electrical noise. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
