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發表於 2020-9-9 00:31:08
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本帖最後由 長長影子 於 2020-9-9 01:08 編輯
我試過用兩條同一長度嘅 USB cable，冇 shielding 嗰條好容易 disconnect。 因此我絶對相信 shielding 會影響 high speed 時嘅 signal integrity。 至於 shielding far-end 端用 cap 接地喺以前 lay digital 板 link-up analog 板，尤其係唔少 audio cable 常用技兩，成條 transmission line 計出嚟大概每 1/4 波長嘅頻率畀佢接地，因此用咩 value 要同選用嘅 cap 嘅 package 都好有關係。 不過我認為 gnd loop 最大影響唔係 digital data 方面，最大問題係個 gnd connection 嘅 shield current 等等影響咗 analog 嗰邊。 如果要係因為 gnd loop 影響 digital audio data 側多數都會係 I2S 嗰類 I/F 先至會因而 induced periodic jitter 等引起失真等問題，第日有機會再分享相關分析嘅量測嘅數據圖表。
我自己音響嗰邊同 music server、NAS 等等，兩邊獨立供電，宜家 network 都係行光纖去 link-up 兩邊，目的係斷開兩邊電源影響以及不必要嘅 gnd connection。
"...So, to summarize, the “right” way to terminate balanced cable, whether for audio or data, is to maintain the twisting as carefully as possible right to the point where it enters equipment (ideally there should be “zero length” of untwisted cable). If the shield is to be terminated, there should be either a concentric connection or the shortest possible pigtail, and it should go straight to the shielding enclosure of the equipment. If the connection is needed to shield against VHF RF but needs to be interrupted at lower frequencies to prevent shield current, a capacitor should be used in series with the shield connection (also with very short leads or a concentric connection), and only at the receive end...."
https://www.ranecommercial.com/legacy/note165.html
https://incompliancemag.com/arti ... rd-about-shielding/ |
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