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Welcome to the April issue of North Hills Analyzer e-Newsletter! This
month's issue focuses on Longitudinal Balance and how to measure
it. Your assistance forwarding this e-Newsletter to interested parties isappreciated.

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Measurement of Longitudinal Balance
The speed of data communications over copper wire pairs is increasing
dramatically due to various new technologies. VDSL, VDSL2, ADSL
and ADSL2, are a few popular examples of techniques used to senddata over copper at high speed. All of these transmission methods areused in the local loop that runs from the telephone line to the customer.
The quality and speed of transmission is affected by signal attenuation.
Longitudinal balance measurements ensure circuits do not have aproblem with crosstalk and random noise.
[CONTINUED ON PAGE 2]

About UsFor over 50 years, North Hills has
been a leading manufacturer ofMIL-STD-1553 Data Bus Products
and Wideband ­Transformers.
Our standard and custom products
offer unmatched performanceand reliability for a wide range of­applications in theMILITARY AEROSPACE andINDUSTRIAL OEM MARKETS.

To SubscribeIf you would like to receive North Hills
Signal Processing e-Newsletters in thefuture please subscribe now.
For questions concerning delivery of thisnewsletter please contact Tony Pereira at516-682-7781 or
tonyp@northhills-sp.com.

Contact Information

North Hills™Signal Processing
A Porta Systems Company

6851 Jericho Tpke., Suite 170
Syosset, NY 11791
Ph. 1-516-682-7740
Fx. 1-516-682-7704

Volume. 3 							May 2008

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Measurement of Longitudinal Balance
Why Measure Longitudinal Balance?
Balanced lines, such as UTP – unshielded
twisted pair – have become the preferredmedium for data transmission. They offer an
inexpensive solution to assure reliable datatransmission by minimizing radiation and pickupof interfering signals.
The degree of balance of these lines is,therefore, an important parameter.
How do You Measure Longitudinal Balance?
In connection with the balanced lines A and B,
shown in Fig.1, we define two signals.

which is the transmitted data signal.
In a perfectly balanced system the impedancesfrom either balanced line terminal to ground areequal, so that an applied transverse signal does
not produce a longitudinal component.
ITU-T Recommendation O.9 deals withmeasurements of balance in communication
Systems. ITU-T is the Standardization Sector ofthe International Telecommunications Union.
Given the two-port balanced system of Fig.
2, The Recommendation defines a number ofbalance to ground measurements:
Longitudinal Conversion Loss (LCL) = VL1 / VT1
Longitudinal Conversion Transfer Loss (LTCL) = VL1 / VT2
Transverse Conversion Transfer Loss (TCTL) = VT1 / VL2

Fig. 1. Balanced Lines AB

The longitudinal or “common mode” signal
VL = (VA + VB) / 2i.e., the voltage between the electrical midpoint of the balanced line and ground, and thetransverse signal
VT = VAB = VA – VB
the voltage between the parallel line terminals,

Fig. 2. Two-Port Balanced System

LCL is also known as the one-port and LCTL as
the two-port longitudinal balance measurement.
The measurements are all expressed in dB, i.e.
as 20log of the voltage ratio.
Fig. 3 Illustrates the measurement of LCL andLTCL using a network analyzer and a longitudinalbalance bridge. The balance bridge includes allthe elements specified in Recommendation O.9Ph. 1.516.682.7740

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1234Measurement of Longitudinal Balance(Continued from page 2)

including a balanced-to-unbalanced transformer
with very high inherent balance to ground.
Note: The LCTL measurement requires anadditional common mode injection circuit.

Links to Relevant Data Sheets:
LBB Series Longitudinal Balance Bridges
800 MHz Longitudinal Balance Bridge
CMI Series of Common Mode Injectors
Links to Relevant Application Notes:LCL (One-Port)LCTL (Two-Port)

Fig. 3. Longitudinal Balance Measurement

Conclusion
In order to deliver reliable broadband services,
it is very important to invest in improving thenetwork infrastructure. In order to minimize
crosstalk and other types of signal attenuation,
longitudinal measurements are vital. The
investment in these measurements helps reduce
customer complaints and service calls.
North Hills offers a complete line of longitudinalbalance bridges for both 50 and 75Ω network
analyzers.

App. Note 156. Measurement ofLongitudinal BalanceApp. Note 162. Testing VDSL
Network End Service Splitters
App. Note 163. Testing VDSL
Remote Customer End Service Splitters
App. Note 164. LBB Series One-Port Calibration ProcedureApp. Note 165. LBB Series Two-Port Calibration Procedure
For more information on North Hills’ extensive
line please visit:
http://www.northhills-sp.com/products-wideband.html

The LBB Series covers impedances from 100 to150Ω over the frequency range from 10kHz to800MHz.
The CMI Series are common mode injectors for
two-port measurements complementing the LBBSeries.

The North Hills LBB Series Longitudinal Bridge ships withits own test termination and storage case.
Patent# US 7,282,903 B2

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For questions concerning delivery of this newsletter,
please contact Tony Pereira at:
North Hills Signal Processing
6851 Jericho Tpke, Suite 170, Syosset, NY 11791
Phone: 1-516-682-7781; Fax: 1-516-682-7704
Email: tonyp@northhills-sp.com
Web: www.northhills-sp.com

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North Hills™Signal Processing
A Porta Systems Company