
P
assive intermodulation
(PIM) products are
becoming a problem in
wireless communications system
design for the following reasons:
• Regulatory bodies are maxi-
mizing spectrum capacity
through reduced band-
width.
• Towers are being shared and
the number of antennas
used for transmit and
receive functions reduced.
• Equipment providers are
increasing transmit power
levels and reducing receiver
sensitivity.
• Equipment providers are
providing trunked architec-
tures, enabling multiple
channel operation in VHF
and UHF bands.
With proper low passive
intermodulation devices and
installation procedures much
can be done to reduce the effects
of this problem.
About Passive
Intermodulation
Passive intermodulation is the
production of new, unwanted
signal frequency components in
passive, nonlinear devices com-
monly found in and around
radio sites. These new signals
can land on existing transmit or
receive frequencies on the same
or an adjacent site, causing inter-
ference.
A partial list of devices that,
when frequencies are mixed,
could potentially generate pas-
sive intermodulation products,
includes the following:
• Cables
• Connectors
• Adapters
• Tx line junctions (such as
tee and stars)
• Filters
• Directional couplers
• Antennas
• Surge protectors
Contributing Factors to
Low-PIM Signal Generation
While standards are still under
development, an acceptable PIM
level is –150 dBc as the magni-
tude for third-order intermodu-
lation products using two
20-watt transmitters. To achieve
this low level of intermodula-
tion, designers are focusing on
corrosion in metal joints and
interfaces, joins and surface
irregularities.
Checklist of PIM-reducing
factors:
Avoid ferromagnetic
materials.
Ensure sufficient plating
thickness if ferromagnetic
base material is used.
Minimize the number of
joint or contact points.
Avoid using dissimilar
metal contact.
Ensure sufficient separa-
tion between dissimilar
metals.
Perform firm, complete sol-
dering/welding or brazing
of joints where possible.
Avoid improper solder
joints as they can break
and/or corrode.
Ensure that contact inter-
faces are free of debris.
Ensure high contact
pressure.
Use silver-plated, soldered
center pin, 7/16 DIN con-
nectors whenever possible.
Specify torque values for
butt joints.
Avoid crimp joints.
6
Nextel will get 10 MHz (two five-MHz blocks) at
1.9 GHz.
7
The FCC valued the 1.9 GHz spectrum at $4.8 billion.
The Commission will give Nextel credit for (1) the spectrum
that it is giving up and (2) the money it pays incumbents
to reband. Nextel will then pay the difference (if any) into
the U.S. Treasury.
8
Nextel must put up a $2.5 billion Letter of Credit to cover
800 MHz retuning costs.
9
An independent Transition Administrator will be
appointed to oversee the administrative and financial
aspects of retuning, with the Commission retaining
authority to review disputes.
10
. The U.S. Comptroller General is to review the legal aspects
of the plan, and the Commission retains the right to
stay the implementation IF the Comptroller General
finds unambiguously that it violates federal law.
11
The FCC adopted an Enhanced Best Practices regime to
deal with interference before rebanding is completed.
12
900 MHz B/ILT licensees will be able to convert their
authorizations to commercial operation.
13
The FCC has deferred a decision on Canadian and
Mexican Border Band Plans, until it can work with the
respective governments. Thus, the Band Plan information
reviewed above applies only to non-Border areas.
14
The FCC wants rebanding completed in
36 months.
The FCC’s Order, Summaries and related documents may be found
here: http://www.shulmanrogers.com/CM/Custom/800MHZ.asp
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2
The Importance of
On-time Certification
All professional cabling installa-
tions require certification. Most
installation projects have a hard
deadline and any delay or sched-
ule slip can have major financial
consequences. Contractors often
pay penalties for each day the
project is behind schedule. This
certification phase is the last
phase of a project, and is often
squeezed in order to complete
the project on time, which
could result in overlooked prob-
lems which have to be fixed
later. In other cases, contractors
put in overtime to get the certifi-
cation phase completed before
the deadline.
A cable certification tool that
provides a fast, accurate, com-
plete solution that streamlines
every aspect of the certification
job is critical to this phase of the
installation—from setup, to
record-fast testing and trou-
bleshooting, to reporting results
to the customer. The right tool
can save contractors consider-
able time and money.
Total Time to Certify
The certification process gener-
ally requires two technicians
working as a team. One techni-
cian connects the main unit of
the tester to the link under test
at the patch panel in the tele-
com room (TR). The other tech-
nician connects the remote
tester to the outlet at the other
end of the link under test. Every
link is tested in this way.
“Total time to certify” means
the amount of time to achieve
the following objectives:
1. Connect to the link under
test on both ends
2. Execute the test
3. Save the test results data
4. Move and be ready to
connect to the next link.
1
All links need to pass the
performance requirements
before the job can be consid-
ered complete.
If the contractor can’t com-
plete the work in day shifts,
he/she will either have to pay
planes. This ubiquitous Wi-Fi
has set the stage for second-gen-
eration IP, or 2gIP, applications
to take the scene.
2gIP applications leverage
open IP-based standards, such as
the Session Initiation Protocol
(SIP), to bind telephony's real-
time communicative power with
business applications and
processes. These 2gIP applica-
tions, accessible via wireless
devices, can aggregate the pres-
ence of a workgroup's members,
who in turn can specify their
availability and media prefer-
ences. If members are needed for
any reason at any time, their
availability is known and the
appropriate communications
can be initiated, allowing the
other team members to reach
them immediately with point-
and-click simplicity. In addition
to checking availability and set-
ting up an audio conference,
users are offered such features as
videoconferencing, document
sharing and whiteboarding.
Say, for example, that a criti-
cal project encounters a problem
that needs immediate attention.
The project leader just landed at
Chicago's O’Hare International
Airport and discovers the prob-
lem upon checking voice mail.
Clearly she needs to consult key
team members immediately to
figure out the next steps.
Unfortunately, her connecting
flight leaves in an hour and her
team is spread across three time
zones, some in branch offices,
some working from home and a
couple others traveling.
Previously, the project leader
would have had to make numer-
ous time-consuming phone calls
to assemble a conference quo-
rum, connecting with a few but
leaving voicemails for others. If
documents were required, such
as contracts or schematics, an e-
mail step was also necessary.
However, with broadband
wireless and a 2gIP presence-
aware collaborative tool, her
options completely change.
With her laptop, PDA or inte-
grated smartphone, she quickly
invokes the application's pres-
ence portal, scans the team
members' availabilities, selects
those who are needed and avail-
able, selects the documents to
send and clicks to set up a multi-
party conference complete with
shared documents.
With that single click, the
application sets up the out-
bound conference and e-mails
documents. It also handles the
mixed media that some may
need to join in the call, if per-
haps one or more can join in
only via instant messaging
because they're in a meeting or
already on another teleconfer-
ence. Does our project leader
make her plane? With 2gIP, she
has a good chance.
In the coming years, the com-
bination of presence-aware col-
laborative tools with 802.11g’s
anywhere/anytime, 54 Mbps
wireless access will wholly trans-
form how we work, play, learn
and interact both with others
and with information. Given the
rapid progress of IP convergence
of fixed and wireless domains as
well as private and public net-
works, it is likely that a single,
highly functional wireless device
will be all we need to take our
world with us while we move
around—always connected, but
in control, and with no penalty
for being mobile.
This article has been reprinted from
the September 1, 2004, issue of
Wireless Week with permission.
Wi-Fi x 5: How 802.11g
Changes the Mobility Picture
(continued from page 1)
Certifying Cable Installations
on Time and Without Penalties
By Hugo Draye, marketing manager copper certification, Fluke Networks
The Nextel / FCC Spectrum
Reallocation: What Does It
Mean for You? (continued from page 1)
Overcoming Passive
Intermodulation in Antenna Design
Submitted by Dave Daniel, director of product management, antenna products, Sinclair Technologies Inc.
(continued on page 25)
(continued on page 17)