Telecommunications Industry Association
TR41.9-09-11-008M1
Document Cover Sheet
Project Number
PN-3-3602-RV
Document Title
Proposed Test Procedure for VDSL/VDSL2 Longitudinal Output Voltage
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: tlawler@cisco.com
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 provides a test procedure for measuring VDSL/VDSL2 Longitudinal Output Voltage.
This test procedure is intended for the revised TSB-31-C (TSB-31-D).
v1.0 – 20050426
Telecommunications Industry Association
TR41.9-09-11-008M1
14.8
Longitudinal Output Voltage, VDSL/VDSL2 Terminal Equipment ANSI/TIA968-B, 5.3.8.3
14.8.1
Background
Longitudinal output voltage (LOV) limits complement PSD limits by restricting the
amplitude of common mode signals much like the PSD limits restrict the amplitude of
the equipment’s differential mode signals. LOV limits are necessary as common mode
signals tend to couple more readily than differential mode signals in multi-line, twisted
pair cable plant. In other words, LOV limits are necessary to limit crosstalk. LOV limits
have been crafted to allow higher levels around the equipment’s operating band. This is
necessary as a common mode image of the desired differential mode signal results
through imbalance in the line interface, cabling and the measurement circuitry. A tighter
limit applies above the equipment’s operating band where the LOV source is usually not
associated with any signal intended to be applied to the line.
VDSL/VDSL2 over POTS modems must also meet certain LOV limits for voiceband
terminal equipment. These measurements can be done by using the procedure set out
in subclasses 9.15 and 9.17.
14.8.2 Purpose
To verify that the longitudinal output voltage is below the limit.
14.8.3
Equipment
(1)
Spectrum analyzer SEL#34.
(2)
LOV Test fixture shown in Figure 14.8-1.
Note: Refer to subclause 5.5 for equipment details.
14.8.4
Equipment States Subject to Test
Transmitting continuously as described in subclause 14.4.2. For VDSL2 modems that
support extended upstream operation, each Extended Upstream (EU) mask number
must be considered.
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14.8.5 Procedure
In this section the criteria frequency range has been divided into two segments. The
number of segments chosen is dependent upon the capabilities of the test equipment.
14.8.5.1 Procedure for Segment 1
(1)
Condition the EUT to transmit continuously as described in subclause 14.4.2.
(2)
Connect the EUT to the test circuit of Figure 14.8-1.
(3)
Set the spectrum analyzer as follows:
Resolution bandwidth: 3 kHz or 4 kHz, if supported by spectrum analyzer
Video bandwidth: 300 Hz
Attenuation or range: Set for minimum without overload
Reference level: (-30) dBV
dB/div: 10 dB
Start frequency: fa Hz (from Table 63 in TIA-968-B)
Stop frequency: 2.5 MHz
Marker Function: Voltage dBV
Limit test: On with limit line programmed with the LOV limit
(4)
Measure and record the LOV averaging the readings over several sweeps.
(5)
Repeat steps 1 to 4 for other Profiles.
(6)
For extended upstream operation, repeat steps 1 to 5 for each supported EU
mask (US0).
14.8.5.2 Procedure for Segment 2
(1)
Condition the EUT to transmit continuously as described in subclause 14.4.2.
(2)
Connect the EUT to the test circuit of Figure 14.8-1.
(3)
Set the spectrum analyzer as follows:
Resolution bandwidth: 3 kHz or 4 kHz, if supported by spectrum analyzer
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Telecommunications Industry Association
TR41.9-09-11-008M1
Video bandwidth: 1 kHz
Attenuation or range: Set for minimum without overload
Reference level: (-30) dBV
dB/div: 10 dB
Start frequency: 2.5 MHz
Stop frequency: See Table 63 of TIA-968-B
Marker Function: Voltage dBV
Limit test: On with limit line programmed with the LOV limit
(4)
Measure and record the LOV averaging the readings over several sweeps.
(5)
Repeat steps 1 to 4 for other Profiles.
(6)
For extended upstream operation, repeat steps 1 to 5 for each supported EU
mask (US0).
Note: A resolution bandwidth (RBW) of 3 kHz is typically used as most spectrum analyzers support
this RBW.
14.8.6
Alternative Methods
None
14.8.7
Suggested Test Data
(1)
Plot of the LOV with the limit line shown
(2)
Upstream signals (US0, US1 & US2) that were measured.
(3)
Line loop lengths that were used to obtain the LOV measurement for the
upstream signals.
14.8.8
Comments
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Telecommunications Industry Association
TR41.9-09-11-008M1
Care must be taken in the construction of the LOV test fixture. Resistor values must be
matched as previously mentioned. Test leads from the fixture to the EUT should be
kept as short as possible to minimize RF ingress. The ground connection to the fixture
should be of a low inductance, kept short, and connected directly to the chassis ground
of the EUT. For EUT’s without an earth ground, a ground plane should be used as
discussed in subclause 9.15.8.
T
50
EUT
0.15 µF
50
R
100
Spectrum
analyzer
NOTE - All resistor values are in ohms, and resistors are to be matched to better than 0.1%.
Use a spectrum analyzer with a high input (>10k) impedance.
Figure 14.8-1 LOV Test Fixture & Connection Diagram, VDSL/VDSL2
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Telecommunications Industry Association
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The following measurement examples are for reference only and are not intended to be
included in TSB-31-D.
Longitudinal Output Voltage
-50.00
-60.00
Voltage (dBV)
-70.00
-80.00
-90.00
-100.00
-110.00
-120.00
10.00 k
100.00 k
1.00 M
Frequency (Hz)
–––– Limit
–––– Result
Segment 1: 12 kHz to 2.5 MHz, Profile 17a, EU-32, loop set to 9kft.
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Telecommunications Industry Association
TR41.9-09-11-008M1
Segment 2: 2.5 MHz to 30 MHz, Profile 17a, EU-32, loop set to 1kft.
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