DXE Technical Note:
Importance of Correct Termination of Shielded Cat5
Networking Cables
By Scott MacDonald, KD8BDX
A computer with an internet connection is an important
tool in today’s ham shack, used for a large variety of
vital purposes. Not only that, but many other pieces of
equipment are incorporating Ethernet ports, to allow
easy interaction with each other, with computers, or for
direct remote access. Conventional thinking is that
network communication is an enclosed system, where
the unshielded twisted pair (category 5 cable, or Cat5
for short) keeps the signaling voltages in and other RF
out. In my own experience I have found this not to be
the case and this tech note is intended to detail some of
the reasons behind this and the construction of shielded
Cat5 that I have found to be the solution.
Twisted pair is used widely when it comes to balanced
communication lines as a constant twist of the wire
helps to merge the magnetic field around the pair and
keep important voltages in and noise out. The problem
is too many cat5 cables do not have a constant twist –
the pairs of conductors are not bonded and any time
the cable is bent the integrity of that balanced pair can
be compromised.
needing the flexibility of custom wiring length and being
comfortable with terminating cat5, I researched cable,
ends, and tools to determine what was the best to use
to make my own shielded, twisted, bonded pair cat5.
Below is a listing of the products used and an illustrated
guide to working with them.
Parts list:
• Belden 7921A DataTuff – Cat 5e, 4pr 24
• Belden 1797B - Cable Tool
• Sentinel 111S08080090C34 – Shielded RJ45
• 3M 1181 – Copper Foil Tape
• Sentinel 900007 – Crimp Tool
• Sentinel B0051 – Black RJ45 Boot
• Xcelite 170M – Side Cutters
Though not shown in this guide, it is recommended that
a wire tester be used to verify that your custom cables
are terminated properly. This is also a useful tool to
check existing wiring or the connection integrity of
premade jumpers.
Note that any substitute for the 3M Copper Tape needs
to have conductive adhesive. If this is lacking, the
continuity of the shield from RJ45 to RJ45 may be
broken.
The second and maybe larger issue is with the lack of
adequate shielding on most cat5 cables. As with any
current-carrying conductor, the magnetic field extends
beyond the size of the wiring itself, so if you are using
UTP (unshielded twisted pair) and it is running
physically against other unshielded low voltage or line
voltage wiring, there is the potential for network noise
to get out or other noise to get into the network.
The best way to ensure your network is not interfering
with your reception is to replace the existing cat5 with
better cabling, specifically Ethernet wiring that is well
shielded, incorporating both shielded RJ45 connectors
and bonded pairs. There are a variety of cables
available online that meet these requirements and
would be sufficient for many applications. With
Trim off outer jacket of 7921A cable with 1797B cable
tool, using an old piece as a guide. If it is your first end,
measure and cut about 1-3/4” – 1-7/8” from a clean
cut, and save the piece of jacket for next time. A deep
score and pop off of the insulation is better than a cut
that is too deep and penetrates the shield.
Cut a piece of copper tape about 1” - 1½”. Wrap tape
on shielding, leaving a small gap from the insulation.
Remove braid, drain line, foil, and plastic to the top
edge of the copper tape, exposing the twisted pairs.
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