Discussion Forums are temporarily in read only mode. All forums are visible but posting is not possible. Please check back shortly.

Thread: Reduce EMI with Shielded LAN Cables


Permlink Replies: 1 - Pages: 1 - Last Post: Sep 26, 2011 2:28 PM Last Post By: raymond_shen
raymond_shen

Posts: 8
Registered: 06/01/11
Reduce EMI with Shielded LAN Cables
Posted: Sep 26, 2011 2:27 PM
Click to report abuse...   Click to reply to this thread Reply
Unshielded LAN cables are often a source of unintentional RF emissions. These emissions may arise from common mode signals, such as switching power supply noise, and are often introduced by Ethernet switches. Most LAN patch cables (category 5 and category 6) are unshielded. Any antennas brought in close proximity to the unshielded cable will detect these emissions. Fortunately, these emissions can be mitigated using shielded LAN cables.

An H-field sniffer probe (Figure 3) connected to the RF sensor was used to detect and localize sources of EMI. When the probe was placed near the unshielded LAN cable, the RF sensor picked up the emissions seen below (Figure 1). This ‘forest’ of spurs near 90 MHz was entirely due to the cable. When the cable was replaced with a CAT6 shielded cable these emissions became almost undetectable (Figure 2). Shielded LAN cable may be purchased at any electronics store.
raymond_shen

Posts: 8
Registered: 06/01/11
Re: Reduce EMI with Shielded LAN Cables
Posted: Sep 26, 2011 2:28 PM   in response to: raymond_shen in response to: raymond_shen
Click to report abuse...   Click to reply to this thread Reply
Clip on RF chokes are less effective. We ran an experiment and applied a 10mm RF choke at the RF sensor end of the LAN cable. We observed no reduction of EMI. We then applied the same RF choke to the switch side of the LAN cable. Again, we observed no reduction of EMI.

Point your RSS reader here for a feed of the latest messages in all forums