I have not been following this thread, so apologies if some of this is a repeat. Twisted pair produces lots of tiny little antennas pointed in varying directions. This is a good thing for both immunity and emissions, as in each case (due to antenna reciprocity) the fields (received or transmitted) largely cancel. In effect twisted pair reduces the loop area. As a result, twisted pair is an effective strategy at low frequencies, where magnetic/inductive coupling dominates. At these frequencies the cable shield is ineffective. Curt Curt McNamara, P.E. // principal electrical engineer Logic Product Development 411 Washington Ave. N. Suite 400 Minneapolis, MN 55401 T // 612.436.5178 F // 612.672.9489 www.logicpd.com / / / / / / / / / / / / / / / / / / / / / / / / / This message (including any attachments) contains confidential information intended for a specific individual and purpose, and is protected by law. If you are not the intended recipient, you should delete this message and are hereby notified that any disclosure, copying, or distribution of this message, or the taking of any action based on it, is strictly prohibited. -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Kevin G. Rhoads Sent: Friday, May 14, 2010 7:21 AM To: Neo Cc: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Why shielded twisted-pair is still twisted? >Is this statement applicable to twin-ax cable? For twin-ax case, the outer >shield >thickness is also just a few mils. Can I say twin-ax also suffer AC power >interference? Simple answer: YES. But the difference is the ratios between interference frequencies and frequencies of interest. Audio band INCLUDES 50 and 60 Hz, much of what is run over Twin-ax is primarily or completely at much higher frequencies. So separating signal from interference by frequency is UNdoable for audio and typically trivial for Twin-ax signals. Of course, if you want to send unmodulated baseband audio over cable, STP will work better than Twin-ax. It is a bit like asking if a 240Z is better than a Kenilworth. What are you trying to do? Haul heavy loads: Kenilworth. Drag racing: 240Z. Comparisons not only involve the things being compared, they also ALWAYS involve a metric of goodness or worth or value. So far your metric has been unstated and implicit, so people have been answering in manners designed to allow you to use your (unstated) metric to compare. There are cases where hum pickup is a total "don't care" and for those any proper metric will assign a zero or negligible weighting to measures of hum pickup. HTH Kevin ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu