MAY 2017 Cabling Installation & Maintenance www.cablinginstall.com 8
Designing and installing fber-optic cabling to support distributed antenna systems continued
bending than in tension, installers need
to be more careful in bending than in
Installers can install connectors by
any one of seven methods: 1) epoxy, 2)
HotMelt adhesive; 3) quick-cure adhesive; 4) crimp and polish; 5) cleave-and-crimp; 6) fuse-on; 7) pigtail splicing.
However, two methods dominate DAS
and no-polish connectors.
No-polish connectors or prepolished
connectors are also known as “spliced
connectors,” as the two types involve
making a splice. Splice-on connectors
require a fusion splicer for installation.
“Cleave-and-crimp” connectors require
a specific tool to make a mechanical
splice in the back shell.
Prior to testing, the installer cleans and
inspects the connectors. Prior to installation, the installer tests preterminated
cables. Such testing verifies lack of damage during shipping.
While one could assume that the
caps contain no dust and that the caps
have been on the connectors for the entire time from assembly to delivery, such
assumptions are often untrue. Caps can
contain dust. Caps can fall from connectors during shipment. Novice installers can wipe connector ends with wrong
material, and even with fingers. Think of
the “wonderful” microscopic appearance
of a connector with skin oil and hand lotion on the core.
Microscopic inspection—Dust on connectors is a common problem. This dust
blocks or diverts light from its normal
path. In addition, it can prevent connectors in a patch panel from making full
contact. Without full contact, connectors
exhibit increased loss and reflectance.
Finally, dust can create scratches on the
fiber core when two connectors mate.
Dust has six sources: 1) dust not
removed by pretermination facility; 2)
dust from inside dirty caps; 3) dust from
connectors without caps for any length
of time; 4) dust transferred from dirty
test leads; 5) dust from unplugged patch
panel or optoelectronic ports; 6) dust
from cleaning with tissues that are not
lens-grade and lint-free.
In short, dust is the demon of fiber-optic connectors.
Test leads—The installer matches the
test leads and launch cables to the fiber
core diameter and to the connector type
of the cables under test. In addition, test
leads are qualified to demonstrate acceptable low loss. Dirty or high-loss connectors can produce only high-loss measurements. High loss results in rejection
of the cables under test.
Insertion loss—The installer performs the insertion loss test in order
to simulate the loss of the transmit-ter-receiver pair. The installer performs the insertion loss test according to the standard test procedure.
For both singlemode and multimode
testing, the recommended procedure is the one-lead reference method.
In the singlemode test, the installer
makes a 1.2-inch-diameter loop on the
source lead. In the multimode test,
the installer uses one of the two encir-cled-flux-compliant methods to measure the input power level.
In troubleshooting or initial link certification, the installer measures the
output power of the transmitter and/or
the power level at the receiver. For this
measurement, use the dBm scale of the
meter of the OLTS.
OTDR—While DAS cables and fi-
ber-to-the-antenna cables serve the
same function, with much of the same
equipment, there is one potential dif-
ference: length. Fiber-to-the-antenna
cables are relatively short and require
a high-resolution OTDR. DAS cables
may be short. However, they can have
significant length in large buildings or
outdoor distributed antenna systems.
Long cables do not require a high-res-
To accurately measure short cables, the installer uses a high-resolution
OTDR. Without one, the installer may
not be able to measure individual connector pairs and segment lengths.
The installer performs the OTDR test
with either one or two launch cables, depending on whether or not the requirement is to measure the loss of the far-end connector from the near end.
If the cable contains splices, the installer tests in both directions to determine the true splice loss, to identify
ghost reflections, and to verify that gainers have acceptable loss.
The installer tests at a minimum of
two wavelengths. Typically the lower
wavelength is that of the optoelectronics.
A comparison of losses at the short and
the long wavelengths reveals the presence
or absence of stress on the fiber.
In summary, DAS and fiber-to-the-antenna systems have similarities and
differences. They are similar in their
functions, in their concern for connector cleanliness, and in the types of testing performed.
They can differ in the cable lengths
and size of areas served. In addition,
they differ in the types of cables used.
Distributed antenna systems use standard data communications cables.
Fiber-to-the-antenna systems use custom hybrid cables. Finally, they differ in
the method of connector installation.
DAS cables can be field-terminated; fiber-to-the-antenna cables are usually
Eric R. Pearson, CFOS/C/S/T/I is principal of
Pearson Technologies Inc. ( www.ptnowire.com).
This article is excerpted from Chapter 31 of
Pearson’s recently published book “Professional
Fiber Optic Installation – The Essentials for
Success, Version 10.”