Characterizing Signal Leakage
from an All-Digital
Cable Network
Presenter: Mario Sebastiani
for
CCTA Technical Training Sessions August 14, 2012 - San Juan, PR
Seminar Summary
Topics review for
all-digital
HFC network:
Is it necessary to patrol for leakage?
Is the leakage spec the same as for analog?
Can QAM signals cause harmful interference?
Can off-air digital ATSC impair QAM signals?
Is CW/Video carrier necessary for patrolling?
What frequency should I troubleshoot egress?
Are vendors providing digital leakage gear ?
Technical Training Outline
Examine reasons for a patrolling leakage program
Demystify leakage characteristics & requirements
Analyze leakage symptoms & measurements
Concerns of leakage in an all-digital network?
Characterising Signal Leakage in an All-Digital Cable Network (Courtesy of SCTE live learning, 2010)
http://www.myeventpartner.com/WebConference/RecordingDefault.aspx?c_psrid=ED50D98486
Demonstration of QAM carrier impaired by analog or digital signals with MER/BER measurements
What is Leakage/Egress?
Definition:
- Undesired emission of RF energy generated by the coaxial plant
- Modulated RF signals radiating or leaking out of the cable network
Leakage & Ingress
Leakage
-
RF energy leaking out of thecoaxial environment
Ingress
-
RF or electricalenergy that enters the coaxial environment
Reason #1
to
Monitor
for Leakage
Off-Air Interference
Broadcast TV signals
Radio Mobile Communications
Public Services
Emergency Services
NCTA/EIA Spectrum Plan
Bande de retour Bande FM Bande moyenne
Bande Hyper Bande supérieure
Fréquences aéronautiques (restrictions d’utilisation) Fréquences Hertzienne (TV)
(usage limité) Fréquences Hertzienne (TV) (usage limité)
Frequency Allocation-Cable & Off-Air
EIA/NCTA Traditionnel Standard Terrestre EIA/NC Traditionnel Standard Terrestre T-7 7 98 A-2 109.275 Bande T 99 A-1 115.275 T-13 43 14 * A 121.25 471.25 1 45.75 15 * B 127.25 477.25 2 2 55.25 55.25 16 * C 133.25 483.25 3 3 61.25 61.25 17 D 139.25 489.25 4 4 67.25 67.25 18 E 145.25 495.25 4 MHz 19 F 151.25 501.25 5 5 77.25 77.25 20 G 157.25 507.25 6 6 83.25 83.25 21 H 163.25 513.25 201 XX 88.1 22 I 169.25 519.25 95 A-5 91.25 7 7 175.25 175.25 217 91.3 8 8 181.25 181.25 96 A-4 97.25 9 9 187.25 187.25 247 97.3 10 10 193.25 193.25 97 A-3 103.25 11 11 199.25 199.25 299 107.7 12 12 205.25 205.25 300 XX 107.9 13 13 211.25 211.25 Bande moyenne Bande haute Bande FM radio et télévison par câble Bande basse Bande basse
Frequency Allocation-Cable & Off-Air
EIA/NCTA Traditionnel Standard Terrestre EIA/NCTA Traditionnel Standard Terrestre 98 A-2 109.275 23 J 217.25 525.25 99 A-1 115.275 24 K 223.25 531.25 14 * A 121.25 471.25 36 W 295.262 603.25 15 * B 127.25 477.25 37 AA 301.262 Radio Astronomie 16 * C 133.25 483.25 38 BB 307.263 615.25 17 D 139.25 489.25 41 * EE 325.262 633.25 18 E 145.25 495.25 42 * FF 331.262 639.25 19 F 151.25 501.25 43 GG 337.262 645.25 20 G 157.25 507.25 44 HH 343.262 651.25 21 H 163.25 513.25 65 471Q 471 777.25 22 I 169.25 519.25 69 495Q 495 801.25 7 7 175.25 175.25 70 501Q 501 8 8 181.25 181.25 71 507Q 507 9 9 187.25 187.25 100 651Q 651 10 10 193.25 193.25 101 657Q 657 11 11 199.25 199.25 157 993Q 993 12 12 205.25 205.25 158 999Q 999 13 13 211.25 211.25 Bande haute
Désignation du canal Porteuse audio (MHz) FRÉQUENCE DE CABLODISTRIBUTION ET DE RADIODIFFUSION (NTSC)
Bande moyenne
* fréquences aéronautiques
FRÉQUENCE DE CABLODISTRIBUTION ET DE RADIODIFFUSION (NTSC) Désignation du canal Porteuse audio (MHz) Bande
super
Bande hyper
Reason # 2
to
Monitor
for Leakage
Regulatory compliance requirements
for spectrum management, public
interest and public safety
Frequency Allocation-Cable & Off-Air
EIA/NCTA Traditionnel Standard Terrestre EIA/NCTA Traditionnel Standard Terrestre 98 A-2 109.275 23 J 217.25 525.25 99 A-1 115.275 24 K 223.25 531.25 14 * A 121.25 471.25 36 W 295.262 603.25 15 * B 127.25 477.25 37 AA 301.262 Radio Astronomie 16 * C 133.25 483.25 38 BB 307.263 615.25 17 D 139.25 489.25 41 * EE 325.262 633.25 18 E 145.25 495.25 42 * FF 331.262 639.25 19 F 151.25 501.25 43 GG 337.262 645.25 20 G 157.25 507.25 44 HH 343.262 651.25 21 H 163.25 513.25 65 471Q 471 777.25 22 I 169.25 519.25 69 495Q 495 801.25 7 7 175.25 175.25 70 501Q 501 8 8 181.25 181.25 71 507Q 507 9 9 187.25 187.25 100 651Q 651 10 10 193.25 193.25 101 657Q 657 11 11 199.25 199.25 157 993Q 993 12 12 205.25 205.25 158 999Q 999 13 13 211.25 211.25 Bande haute
Désignation du canal Porteuse audio (MHz) FRÉQUENCE DE CABLODISTRIBUTION ET DE RADIODIFFUSION (NTSC)
Bande moyenne
* fréquences aéronautiques
FRÉQUENCE DE CABLODISTRIBUTION ET DE RADIODIFFUSION (NTSC) Désignation du canal Porteuse audio (MHz) Bande
super
Bande hyper
Spectrum Chart
Aircraft Radio & Navigation
CH
98
CH99
CH14
CH15
CH16
108MHz
139MHz
Cable
Off-Air
123MHz 129MHz 135MHz
Aeronautical Service Bands
111MHz 117MHz
Spectrum Chart (cont’d)
CH 41
Aircraft Radio & Navigation
CH 42
324MHz
336MHz
Cable
Off-Air
327MHz 333MHz __Aeronautical Service Bands
FCC/IC Regulations & Procedures
for Leakage Measurement
< 54 MHz & > 216 MHz = 15µV/m @ 30m
> 54 MHz & < 216 MHz = 20µV/m @ 3m
Use a calibrated half-wave dipole antenna
Antenna must be elevated 3 meters off the
ground and positioned 3 meters from the
leakage source
Patrolling for Leakage
30 meters
3
meters2
µVmµV/M
Standard unit of measure for Leakage
50 Ohm off air measurement
Voltage developed in 1 meter of
infinitely thin section of wire submerged
in a leakage field, produces 1µV of
Polarization Angle
Dipole
Monopole
Cumulative Leakage Index (CLI)
CLI is the net effect of the combination of all
the leaks in the system added together
These cumulative leaks form an invisible
cloud of unwanted RF energy over the cable
system
Required Actions
All leaks 20 µV/m must be logged and
fixed
Only leaks above 50 µV/m are used in CLI
calculation
All measurements taken outside 108-139
MHz must be converted as if they were
taken within the band
Reason #3
to
Monitor
for Leakage
Improves System Performance
Reduces Repeat Service Calls
Common Causes
70% of all leakage is caused by problems
between the tap and entry to the house
– Aging and environmental stress
– Physical trauma to cables or connectors – Loose drop connectors
– Inferior quality coaxial cable, passives, or connectors
Other Causes of Leakage
Improperly installed connectors
Cracks in the distribution and feeder cable
Animal chews
Poorly-shielded drop cable
Bad connectors at the tap
Bad/loose port terminators
Other Causes (Cont’d)
Customer installed equipment
Damaged amplifier housing or loose lids
Loose tap plates
Broken tap ports
Poor installation of splices and connectors
Tools
Dipole
●
Standing Waves
Electrical Noise
Characterizing Signal Leakage
from an All-Digital Cable Network
• Ron Hranac and Ray Thomas (Comcast)
have conducted field tests on the subject a
couple of years ago
• SCTE live Learning presentation on the
subject
• http://www.myeventpartner.com/WebConf
erence/RecordingDefault.aspx?c_psrid=E
D50D98486
Characterizing Signal Leakage
from an All-Digital Cable Network
Field tests were conducted in the Denver, Co area using an analog CW carrier and a 256
QAM carrier
CW test frequency was Ch. 18 @145.25 MHz Digital test with 256QAM carrier @ 147Mhz Digital test with power -6dBc from CW (video)
Testing leakage carrier in between 2 QAMs
Characterizing Signal Leakage
from an All-Digital Cable Network
Review the characteristics of the analog and digital carriers
Review type of modulation
Where the RF energy is located
Historical test instruments to measure leakage
Troubleshooting gear
MER/BER performance behavior being deteriorated by signal ingress
Analog A/V Carriers
4.5 MHz 3.59 MHz 6.0 MHz 0 -10 -20 -30 -40 -50 -60 -70 dB 4.2 MHz Video Carrier Audio Carrier Sous-porteuse couleur 1.25 MHz 3.58MHz Amplitude Modulation FM Modulation +/- 25 KHzAnalog C/I Objective Table
Red designates Visible interference Green designates Non-visible interference 4.5 MHz 3.59 MHz 6.0 MHz 0 -10 -20 -30 -40 -50 -60 -70 dBCharacterizing Signal Leakage
from an All-Digital Cable Network
Conclusion from Hranac/Comcast test results:
Leaks from digital QAM carriers can cause
harmful interference to terrestrial users just like analog carriers
Terrestrial RF energy can impair on QAM
signals depending on the level of the ingress
Patrol leakage program should apply to all-digital systems
The compliance spec for all-digital networks is similar as for analog cable systems
Characterizing Signal Leakage
from an All-Digital Cable Network
Summary and conclusion of SCTE tests (cont’d):
A CW carrier is still the most cost/efficient method for testing and troubleshooting leakage
The minimum frequency offset allocation to a QAM is 1 MHz
The frequency range for leakage detectors can be from 108MHz ~147MHz (Aeronautical band)
Allocating CW carrier between 2 QAM carriers will impair on both QAM carriers
Characterizing Signal Leakage
from an All-Digital Cable Network
Summary and conclusion of SCTE tests (cont’d):
Some manufacturers are working on or already supplying leakage detection tools for digital QAM carriers
Cost efficiency of digital leakage instrumentation will accelerate its deployment in all-digital cable systems
Leakage – Downstream Ingress – Facts
• Being leakage compliant with rules and
regulations increases the figure of merit of
the HFC network
• Higher MER levels throughout the RF
plant - greater signals reliability
• The average MER objective at the
subscriber tap of 33dB ~ 35dB
P
Operating margin Zone Risk Zone RS-FEC Crash ZoneMER TARGET - THE “CLIFF” EFFECT
Upstream 16 QAM >22dB 22dB - 20dB <17dB Objective
UP/Downstream 64 QAM >28dB 28dB - 26dB <23dB P- BER CER
Downstream 256 QAM >33dB 33dB - 31dB <28dB 1 x10-8 9 x10-7
Constellation Performance
QAM EVS
Troubleshooting in-channel ingress is
easy with
QAM EVS
mode
Typical ingress areas
• Loose connector • Broken shields • Tap plate loose • Home wiring
• CSO/CTB from house amp • Sweep inter-mod
BER
Digital signals work well until very close to the point of failure Measurement of digital carriers is critical in determining the system margin
Signal level
MER
Pre/Post BER
CER (Codedword Error Rate)
The BER helps to find problems related to point of failure.
Gray lines designate marginal signal quality
BER/CER
BER
Pre: before FEC repair Post: after FEC repair
ERRORS
Corr = corrected codewords
uncor = uncorrectable codewords err sec = errored seconds
sev sec = severely errored seconds
Codeword Error Rate: Objective = 9x10⁻⁷
MER/BER Demonstration
Characterizing Signal Leakage
from an All-Digital Cable Network
Thank you, Gracias, Danki, Merci
to the CCTA members
Mario Sebastiani: msebastiani@incospec.com
http://www.incospec.com/resources/webinars/webinars.php
“Serving the industry since 1978
with pride, integrity and commitment”
Tools
Dipole
●