Download 14.7 Transverse Balance, VDSL/VDSL2 ANSI/TIA-968

Telecommunications Industry Association
TR41.9.2-09-11-011M1
Document Cover Sheet
Project Number
PN-3-3602-RV
Document Title
Proposed Test Procedure for VDSL/VDSL2 Transverse Balance
Source
Cisco Systems, Inc.
Contact
Tim Lawler
170 West Tasman Dr.
San Jose, CA 95134
Distribution
TR-41.9, at the November 2009 meeting
Intended Purpose
of Document
(Select one)
X
Phone: (408) 527-0681
Fax: (408) 526-4184
Email: [email protected]
For Incorporation Into TIA Publication
For Information
Other (describe) -
The document to which this cover statement is attached is submitted to a Formulating Group or
sub-element thereof of the Telecommunications Industry Association (TIA) in accordance with the
provisions of Sections 6.4.1–6.4.6 inclusive of the TIA Engineering Manual dated March 2005, all of
which provisions are hereby incorporated by reference.
Abstract
This contribution provide test procedure for measuring VDSL/VDSL2 Transverse Balance. This test
procedure is intended for the revised TSB-31-C (TSB-31-D).
v1.0 – 20050426
Telecommunications Industry Association
TR41.9.2-09-11-011M1
14.7
Transverse Balance, VDSL/VDSL2 ANSI/TIA-968-B, 5.3.8.2
14.7.1
Background
See subclause 10.1.1.
14.7.2 Purpose
To determine transverse balance of VDSL/VDSL2 EUT.
14.7.3 Equipment
(1)
Spectrum analyzer SEL#34
(2)
Tracking generator SEL#39.
Note: Refer to subclause 5.5 for equipment details.
14.7.4 Equipment States Subject To Test
Active state with appropriate grounding applied and the EUT transmitter turned off.
Note: Terminal equipment may require special attention to ensure it is properly configured for this
test. For example, if the equipment would normally be connected to ac-power ground, coldwater-pipe ground, or if it has a metallic or partially metallic exposed surface, then these points
are connected to the test ground plane. Similarly, if the EUT provides connections to other
equipment through which ground may be introduced to the equipment, then these points are
connected to the test ground plane. Equipment that does not contain any of these potential
connections to ground are placed on a conductive plate that is connected to the test ground
plane (see comment 1); this applies to both non-powered and ac-powered equipment.
14.7.5 Procedure
(1)
Connect the 100 ohms calibration test resistor (RCAL) to the test circuit of Figure
14.7-1.
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Telecommunications Industry Association
(2)
TR41.9.2-09-11-011M1
Set the spectrum analyzer and tracking generator to the appropriate frequency
ranges:
(a)
For VDSL over POTS - 13.6 kHz to 12,000 kHz
(b)
For VDSL2 over POTS profiles 8a, 8b, 8c, and 8d - 13.6 kHz to 8,500 kHz
(c)
For VDSL2 over POTS profiles 12a and 12b - 13.6 kHz to 12,000 kHz
(d)
For VDSL2 over POTS profiles 17a - 13.6 kHz to 20,000 kHz
(e)
For VDSL2 over POTS profiles 30a - 13.6 kHz to 30,000 kHz
(f)
For VDSL2 all digital mode profiles 8a, 8b, 8c, and 8d - 200 Hz to 8,500 kHz
(g)
For VDSL2 all digital mode profiles 12a and 12b - 200 Hz to 12,000 kHz
(h)
For VDSL2 all digital mode profiles 17a - 200 Hz to 20,500 kHz
(i)
For VDSL2 all digital mode profiles 30a - 200 Hz to 30,000 kHz
(3)
Adjust the tracking generator voltage to measure a VM of 0.316 Vrms across the
calibration test resistor of 100 ohms.
(4)
Connect the spectrum analyzer across the RL resistor (90 or 500 ohms as per
ANSI/TIA-968-B, Table 62).
(5)
Adjust capacitor C1 until a minimum voltage across the RL resistor is obtained.
This represents the highest degree to which the bridge can be balanced. The
result of this balance calibration should be at least 20 dB better than the
requirement for the applicable frequency band. If this degree of balance cannot be
attained, further attention should be given to component selection for the test
circuit and its construction.
(6)
Reverse the polarity of the tip-and-ring pair under test. If the transverse voltage
(VL) changes by less than 1 dB, the calibration is acceptable. If the transverse
voltage changes by more than 1 dB, it indicates that the bridge needs further
adjustment to accurately measure the balance of the EUT. Repeat the calibration
process until the measurements differ by less than 1 dB while maintaining the
balance noted in step (5) above.
(7)
Replace the calibration resistor with the tip-and-ring pair of the EUT.
(8)
Measure the voltage across the tip and ring of the EUT; this is the metallic
reference voltage (VM).
(9)
Measure the voltage across the RL resistor; this is the longitudinal voltage (VL).
(10)
Calculate the balance using the following formula:
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Telecommunications Industry Association
TR41.9.2-09-11-011M1
TransverseBalance 20logV M
V
L
Note: If the readings are, for example, taken in dBV, then the equation may be simplified to:
Balance ( dB )  V
(11)
M
( dBV )  V L ( dBV )
Reverse the tip and ring connections of the EUT and repeat step (8) through step
(10). The lesser of the two results is the transverse balance of the EUT.
14.7.6 Alternative Methods
See Appendix C.
Note: The test method that is described in Appendix C may be more appropriate to use for frequencies
above 3 MHz.
14.7.7 Suggested Test Data
(1)
Frequencies tested.
(2)
Balance measured for the EUT.
(3)
Calibration balance measured.
14.7.8 Comments
(1)
EUT that is not normally grounded should be set in its normal position directly on a
conductive plate. It is recommended that the overall area of the conductive plate
be at least 50% greater than that of the base of the EUT. This represents the
closest proximity to ground that is likely to be encountered by the EUT.
(2)
Interference from power frequency harmonics can be minimized by using test
frequencies midway between multiples of 60 Hz.
(3)
In some cases, EUT may apply internally generated signals to the test set. Such
signals should not be construed as part of the transverse balance test.
(4)
Test leads between the test fixture and the EUT will affect the calibration and EUT
balance measurements. Such cables must be in place when making the
calibration balance adjustments.
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Telecommunications Industry Association
T1
TR41.9.2-09-11-011M1
1:1 impedance ratio, 100 ohm wide-band transformer.
Optimally a dual-stator air-variable RF capacitor that maintains a constant
20pF
capacitance between stators while providing a variable capacitance from either
Differential
stator to ground.
3 pF
Composition RF capacitor
RCAL
100 ohms
RL
90/500 ohms: A non-inductive precision resistor
(chosen according to Table 62 of ANSI/TIA-968-B).
Note 1.
The 3 pF capacitor may be placed on either line of the test set, as required, to obtain
proper balancing of the bridge.
Note 2.
The effective output impedance of the tracking generator should match the 100 ohms test
impedance. The spectrum analyzer's input should be differentially balanced to measure
VM.
Figure 14.7-1 Transverse Balance, VDSL/VDSL2
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