Produits de la Marque EnGenius

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.

Nextel will get 10 MHz (two five-MHz blocks) at

1.9 GHz.

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.

Nextel must put up a $2.5 billion Letter of Credit to cover

800 MHz retuning costs.

An independent Transition Administrator will be

appointed to oversee the administrative and financial

aspects of retuning, with the Commission retaining

authority to review disputes.

. 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.

The FCC adopted an Enhanced Best Practices regime to

deal with interference before rebanding is completed.

900 MHz B/ILT licensees will be able to convert their

authorizations to commercial operation.

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.

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

THE WIRELESS JOURNAL

Market Focus

*For your current pricing and our complete product offering, visit TESSCO.com or call TESSCO.

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.

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)

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