Poslední příspěvky1
Sítě / Re:Tech info ohladom uzemnenia racku
« Poslední příspěvek od CFM kdy Dnes v 05:57:48 »Věčné téma, kde koluje spousta pověr. Ty nejčastěji vychází ze specifických (a často zastaralých) případů zabývajících se NF technikou, které nejsou pro high-speed rozhraní a rušení v řádu MHz až GHz relevantní. Přihodil bych pár odkazů k přemýšlení:
https://ris.utwente.nl/ws/portalfiles/portal/263929833/2019_EMC_Europe_Barcelona_Two_Sided_Earthing.pdf
The results show that STP cables with earthing at both-ends can withstand higher disturbance levels than all other tested configurations. The single-end earthed STP cables give similar results as an UTP cable.
https://www.emcstandards.co.uk/files/part_2_text_and_graphics_21_may_09.pdf
To obtain the full EM performance that a shielded cable is capable of, it is important to electrically bond the shield correctly at both ends of the cable. ... (Many people who are not EMC engineers and have never tried to get a product through EMC compliance tests will be horrified by the idea of the ‘ground loops’ that will result from bonding cable shields at both ends, but in fact if the good modern electronic design techniques described in this series are used, ground loops do not cause problems even with the most sensitive circuits, as discussed later.) As was mentioned earlier, correctly terminating a shield requires 360° shielding to be maintained right through all connectors or glands, to another shielded cable or a metal (or metallised) enclosure.
https://interferencetechnology.com/differential-transfer-impedance-of-shielded-twisted-pairs/
As important as a shield with low Zt is its low-impedance termination to the equipment metal boxes. The connection by which the shield itself is grounded to the equipment box (or PCB) has its own impedance, too. This impedance consist of the shield-to-backshell contact, the connector-to-receptacle impedance (that may include some seam leakage inductance) and the receptacle-to-chassis contact resistance.
https://ntrs.nasa.gov/api/citations/20080021261/ownloads/20080021261.pdf
Numerous sources have shown that grounding the shield at one end will eliminate much of the capacitive coupling, but grounding it at both ends is required to reduce inductive coupling. ... Capacitive coupling: Note that for longer cables, the shield must be terminated periodically (e.g. every λ/10) to achieve this effect.
https://www.emcstandards.co.uk/cable-shield-grounded-at-one-end-only
An SPG (single point gnd) cable shield is a hi-pass filter to magnetic fields and a lo-pass filter to electric fields with amplification at the break frequency.
Ale možná to v síťařině funguje jinak ...
https://ris.utwente.nl/ws/portalfiles/portal/263929833/2019_EMC_Europe_Barcelona_Two_Sided_Earthing.pdf
The results show that STP cables with earthing at both-ends can withstand higher disturbance levels than all other tested configurations. The single-end earthed STP cables give similar results as an UTP cable.
https://www.emcstandards.co.uk/files/part_2_text_and_graphics_21_may_09.pdf
To obtain the full EM performance that a shielded cable is capable of, it is important to electrically bond the shield correctly at both ends of the cable. ... (Many people who are not EMC engineers and have never tried to get a product through EMC compliance tests will be horrified by the idea of the ‘ground loops’ that will result from bonding cable shields at both ends, but in fact if the good modern electronic design techniques described in this series are used, ground loops do not cause problems even with the most sensitive circuits, as discussed later.) As was mentioned earlier, correctly terminating a shield requires 360° shielding to be maintained right through all connectors or glands, to another shielded cable or a metal (or metallised) enclosure.
https://interferencetechnology.com/differential-transfer-impedance-of-shielded-twisted-pairs/
As important as a shield with low Zt is its low-impedance termination to the equipment metal boxes. The connection by which the shield itself is grounded to the equipment box (or PCB) has its own impedance, too. This impedance consist of the shield-to-backshell contact, the connector-to-receptacle impedance (that may include some seam leakage inductance) and the receptacle-to-chassis contact resistance.
https://ntrs.nasa.gov/api/citations/20080021261/ownloads/20080021261.pdf
Numerous sources have shown that grounding the shield at one end will eliminate much of the capacitive coupling, but grounding it at both ends is required to reduce inductive coupling. ... Capacitive coupling: Note that for longer cables, the shield must be terminated periodically (e.g. every λ/10) to achieve this effect.
https://www.emcstandards.co.uk/cable-shield-grounded-at-one-end-only
An SPG (single point gnd) cable shield is a hi-pass filter to magnetic fields and a lo-pass filter to electric fields with amplification at the break frequency.
Ale možná to v síťařině funguje jinak ...
