On 8/26/2017 9:07 AM, Lynn W. Taylor, WB6UUT wrote:
That said, the short xDSL part isn't supposed to radiate.
"Supposed" is the key word here. Radiation occurs due to several mechanisms.
1) Poor circuit layout inside equipment that is also poorly shielded. That wiring radiates.
2) Poor common mode isolation of wiring connected to equipment. On paired cable, a low quality output transformer or poorly balanced output stage puts common mode on the cable. On coax, a Pin One Problem puts common mode on the cable. The cable radiates, just like any other antenna. Power supply wiring is also a potential radiator, and the power supply itself is often a noise source (if it's switch-mode).
3) Poor quality paired cable. Structured cable (CAT5/6/7) is, in general, pretty high quality twisted pair, but quality also varies with manufacturer. Belden, for example, builds its structured cable from molded pairs, which makes their construction more uniform, which minimizes radiation/reception of differential mode signals. By contrast, parallel wire cables have lousy rejection (20-40 dB worse) and are prone to radiation and reception of ANY interfering signal, from audio to VHF.
As an example of #3, zip cord, glorified or otherwise, is TERRIBLE speaker cable, because it is a sitting duck for any audio or radio frequency noise. When I lived in Chicago, solved a lot of RFI from broadcast TV to hi-fi systems by replacing zip cord speaker cables with twisted pair.
Sadly, most modern local telco wiring is either poor quality twisted pair or not twisted at all. Using this wiring for DSL is an open door to RFI.
These, and other issues related to RFI, including CATV and DSL systems, are addressed in detail in several app notes and tutorials on my website. k9yc.com/publish.htm
73, Jim K9YC 73, Jim 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 Message delivered to [email protected]
