Thanks for sharing the knowledge and I'm sure it is based on <painful> experience.
-----Original Message----- From: Flexedge [mailto:[email protected]] On Behalf Of Tim Ellison Sent: Monday, December 03, 2012 6:54 PM To: [email protected] Subject: Re: [FlexEdge] Type of RJ45 connector on 6000 series, Stan Williams VE3FLW Bear in mind that the recommendations by cable vendors are not taking into account that the Ethernet device in this case is a 100W RF signal generator. The same RF that can flow down the shield of a Firewire cable due to common mode RF currents that can lock up a PC can also flow down the shield of a STP Ethernet cable and lock up an Ethernet switch too. A different dynamic you need to considerwhen visualizing this system. Tim Ellison On 12/3/2012 3:45 PM, Stan Williams wrote: > Thanks Tim for your response. I am glad to hear that the 6000 series > uses shielded RJ-45 connectors. > > We agree that the newer CAT6 and 6A cables have better alien signal > rejection due to their tighter and quality controlled twist structure, > as well as the balanced nature of the Ethernet physical units. We > also agree that grounding only one end of a shielded cable will avoid > ground differential common mode signals. > > I do question, however, your assertion that a STP or SSTP cable will > inject alien signals into the cable's inner pairs when grounded at both ends. > Studies and practice demonstrate that the alien signals injected, > below 30Mhz where they will penetrate the shield, are substantially > lower than if there were no shield (20-40db). > > Sample reference: > http://www.gocsc.com/UserFiles/File/Siemon/WPShieldedMythCUS.pdf is > written by a STP cable manufacturer. > > My shack has an isolated ground so I would choose to use SSTP cable > between everything inside that ground perimeter and ensure that the > connection to the backbone is through an unshielded RJ-45 connector. > The backbone is also shielded but again it doesn't cross different ground systems. > > > > -----Original Message----- > From: Flexedge [mailto:[email protected]] On Behalf Of > Tim Ellison > Sent: Sunday, December 02, 2012 11:30 AM > To: [email protected] > Subject: Re: [FlexEdge] Type of RJ45 connector on 6000 series, Stan > Williams VE3FLW > > The RJ-45 connectorshell on the FLEX-6000 is grounded, but we are not > recommending the use of shielded Ethernet cables with the FLEX-6000. > > There are two concerns here; emitted RF from the Ethernet cable and > its susceptibility to RFI ingress. Let's address the later first. > > UTP (unshielded twisted pair) cable is by its very nature, balanced > and very immune to RFI and has very good noise rejection > characteristics due to the differential signaling methodology used for twisted pair Ethernet. > > Shielded twisted pair (STP) CAT cable is only really effective if > physical connection does not create a ground loop, a difference in > voltage potential between the chassis grounds (a DC path between the > two), which can cause excessive common mode currents on the shield and > provide an ingress point for RFI. The only place I have seen it be > effective is in telco COs where EVERYTHING is at the same ground > potential and the equipment is designed to be used in that type of > grounding system (NEBS compliance) > > In the shack, you would need to ensure that everything is connected to > the same ground potential, there are no ground loops via the AC safety > ground and that you are connecting the right ground plane in the > equipment to the grounding system. Since creating the ideal grounding > infrastructure involves a lot of careful engineering, it is easy to > miss something, therefore it is better to use UTP and not induce a new > problem where one did not exist in the first place. STP network cable > can be useful in demanding electrical environments, such as > environments are where the network cable is located in parallel with > electrical mains supply cables or where large inductive loads such as motors. This is usually not the case in the shack. > > Additionally, the physical Ethernet interface (port) is transformer > coupled for DC isolation, which eliminates ground loops between the > connected equipment. Adding STP into the equation could negate that > inherent isolation. You could take a STP cable and replace one end > with a non-conducting connector and make sure you connect the > connected connector to equipment that has a very good RF ground, but I digress. > > From the standpoint of your Ethernet cabling emitting RFI, the > second concern listed above, if the network device/hardware is > emitting RFI, this is because the equipment it is connected to is very > poorly engineered and does not have sufficient filtering. It probably > is not FCC Class B compliant (any more). The FLEX-6000 will be > compliant for CE emission standards, which are more stringent than the > FCC. In these cases where the equipment is radiating, RF interference > suppression is best effected by employing ferrite beads at the cable > end connected to the offending equipment or on the power cord. > Consumer network equipment that use "wall warts" are especially guilty > of being RFI emitters. STP cabling can also be effective in reducing > RFI emissions, but only if they are grounded properly and the RFI > isn't coming from the equipment's ground plane itself. In this later > case, STP will make to problem worse by the cable shield becoming a very effective radiator. > > So, I as initially said, using STP vs. UTP Ethernet cabling can be > problematic and actually make issues worse, which is why it is not > recommended for use with the FLEX-6000. > > Tim Ellison > On 12/1/2012 10:54 PM, Stan Williams wrote: >> The best network cables in high RF environments are shielded, for >> example CAT6A shielded (STP) or double shielded (SSTP) with shielded >> RJ45 type connectors. For these to be most effective at least one >> end should be connected to a box that is grounded. >> >> >> >> Do the 6000 series have shield continuing RJ45 connectors so the >> station ground may protect the CAT cables? >> >> _______________________________________________ >> Flexedge mailing list >> [email protected] >> http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz >> This is the FlexRadio Systems e-mail Reflector called FlexEdge. It >> is > used for posting topics related to SDR software innovation and other > technical SDR topics. > > _______________________________________________ > Flexedge mailing list > [email protected] > http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz > This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is > used for posting topics related to SDR software innovation and other > technical SDR topics. > > > _______________________________________________ > Flexedge mailing list > [email protected] > http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz > This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software innovation and other technical SDR topics. _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software innovation and other technical SDR topics. _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software innovation and other technical SDR topics.
