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?
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_______________________________________________
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[email protected]
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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.
