sweep overview mark ortel sales support eng. © 2005 jdsu. all rights reserved.jdsu confidential...

Sweep Overview

Mark Ortel

Sales Support Eng

© 2005 JDSU. All rights reserved. JDSU CONFIDENTIAL & PROPRIETARY INFORMATION2

Conditioning the Network for Triple Play Services

Know Your HFC Network

System Sweep and Ingress Suppression

Testing and Hardening the Drop (Home Wiring)

Line Conditioning to Optimize Two-way Plant Performance

Fiber Optic Testing Maintenance


Web BrowsingE-mail

Digital MusicVoIP

Digital Photos

Video on Demand

Video Mail

Online Gaming

Podcasting

Video Blogs

High Definition Video on Demand

All Video on Demand Unicast per Subscriber

Meg

abit

s p

er S

eco

nd

20

10

30

40

50

60

70

80

90

100

Time

Bandwidth Demand is Growing Exponentially


Voice Quality Impairments – it’s not always the plant!

PSTN

Cable

CMTS

CMTS

CMTS

Aggregationswitch

Core IPNetwork

HUB SITE

MEDIA POP

MEDIA POP

Trunk MediaGateway

Trunk MediaGateway

CableModem

MTA POTSPhone

HOMEBackground noise, handsetspeaker/mic interference,inadequate volume, insidewiring, mis-configured MTA

(CoS-Diffserv / firewallsettings), wireless phonedelay exacerbates echo

problems, MTA DSP/echocanceller performance

CABLE PLANTRF downstream and/or

upstream errors leading toIP packet loss, bandwidthcapacity limitations (esp.upstream) may lead to

CMTS congestion (droppedIP packets) and excessive

jitter (packet drops by codec)

Customer Problem?Cable Provider

Problem?

HUB SITEExcessive NE pollingand/or high utilization

lead to congestioncausing jitter, droppedpackets and increased

transit delay

UPSTREAM orDOWNSTREAM?

What’s the problem?

CORE IP NTWKHigh utilization lead to

congestion causing jitter,dropped packets and

increased transit delay,mis-configured routing

can cause inappropriatehops leading to increased

latency

MEDIA GW POPDSP codec

performance, echocanceller config., jitterbuffer config. / packet

drops

Telco Problem?

PSTNanalog problems on PSTNpath passed through to IP

network

Cable Provider Problem?

Where is the Problem?

What is the Problem?

CMTS-Blade-Port or Switch-

Slot-Port?


Router-Slot-Port?

LSP/VLAN, Route?


MediaGW-Slot-Port?DSP Card-Port-CPU?



‘Pre-HFC’ Networks

No Optics Standardized ‘Tree & Branch’ Architecture Few Amplifier Types Limited Operating Levels

Networks were optimized for forward plant performance with minimal reverse plant engineering.


‘Pre-HFC’ Networks

No Optics Standardized ‘Tree & Branch’ Architecture Few Amplifier Types Limited Operating Levels

Networks were optimized for forward plant performance with minimal reverse plant engineering.

Headend


HFC Networks

Combines fiber optics with coaxial distribution network Return path is more sensitive than the forward path Most of the ingress comes from home wiring on low value

taps Wide variety of hardware with many connectors

Today’s ‘HFC” networks must be optimized for both forward and reverse performance


HFC Network Architecture

NODE


CMTS

Downstream 0

Upstream 0

Upstream 1

Upstream 2

Upstream 3

Cable Modems

Cable Modems

Cable Modems

Cable Modems

Fiber Nodes

Basic DOCSIS® NetworkDownstream Laser and

Upstream Optical Receivers

Coax Fiber Coax


Types of Lasers used in HFC Networks

Fabry-Pérot (FP) – Less Expensive– Mediocre Performance– No Isolation or Cooling Required

Distributed Feedback (DFB)– Expensive– High Performance– Isolation and Cooling Required


Forward System

Diverging System Constant Outputs with Variable Inputs Fixed Signals

– video / audio / digital carriers

System Noise– is the sum of cascaded amplifiers

Balance or Align (Sweep)– compensate for losses before the amp


Forward Path Unity Gain

OUT+36 dBmV

OUT+36 dBmV

OUT+36 dBmV

OUT+36 dBmV

AMP # 1 AMP # 2 AMP # 3

AMP # 4

IN+12 dBmV

IN+11 dBmV

IN+10 dBmV

2 dB

8 dB 24 dB @ 750 MHz 23 dB @ 750 MHz

18

dB

@ 7

50

MH

z


Reverse System

Converging System Constant Inputs with Variable Outputs No Fixed Signals

– impulse digital carriers

System Noise– is the sum of all active components

Balance or Align (Sweep)– compensate for losses after the amp


Return Path Unity Gain

IN+20 dBmV

IN+20 dBmV

IN+20 dBmV

IN+20 dBmV

AMP # 1 AMP # 2 AMP # 3

AMP # 4

OUT+24 dBmV

OUT+26 dBmV

OUT+30 dBmV

2 dB

8 dB 4 dB @ 40 MHz 4 dB @ 40 MHz

2 d

B @

40

MH

z


Ingress and electrical noise

Common Path Distortion (CPD)

Thermal (intrinsic) noise

Laser clipping noise

Micro-Reflections

Reverse Path Impairments


There are a variety of impairments that can affect two-way operation.

They are classified in three main categories: stationary impairments, which include thermal noise, intermodulation distortion,and frequency response problems; transient impairments, which include RF ingress, impulse noise, and signal clipping; and multiplicative impairments, which include transient hum modulation and intermittent connections.



Thermal noise —The majority of thermal noise is generated in active components. Besides choosing active equipment with a relatively low noise figure, there is little else that you can do about the thermal noise in active devices, other than ensure proper network alignment.



Intermodulation distortion—The most common types of intermodulation distortion affecting the reverse path are second and third order distortions. These can be generated in amplifiers and reverse lasers. A more troubling type of intermodulation can occur in some passive components. It is known as common path distortion (CPD), and usually occurs at a dissimilar metals interface where a thin oxide layer has formed.



Frequency response— Frequency response problems are due to improper network alignment, unterminated lines, or damaged components. When reverse frequency response and equipment alignment have been done incorrectly or not at all, the result can be excessive thermal noise, distortions, and group delay errors.



RF ingress — The 5-40 MHz reverse spectrum is shared with numerous over-the-air users.


Signals in the over-the-air environment include high power shortwave broadcasts, amateur radio, citizens band, government, and other two-way radio communications.


Downstream and Upstream Noise Additions

Headend Headend

Reverse System “Noise Funneling”

Ingress from seven amplifiers ends upat the headend.

Forward Signals

Noise

Noise


Impulse noise —Most reverse data transmission errors have been found to be caused by bursts of impulse noise. Impulse noise is characterized by its fast risetime and short duration.

Common sources include vehicle ignitions, neon signs, static from lightning, power line switching transients, electric motors, electronic switches, and household appliances.



Impulse Noise in the Upstream


Sample: “Loose Plant” Performance History

• Average noise floor at 17 MHz varies consistently by time of day

• Indication of return path with an ingress problem.

•Maintenance now will prevent future problems

Single Frequency Time Window for 72 Hours from one return path

7:00AM 11:00PM 7:00AM11:00PM


Sample: ‘Tight’ Performance History

• 17 MHz noise floor tracked over time

• Average noise floor stays fairly flat and consistent over the 3 day period

Single Frequency Time Window for 72 Hours from one return path

Peak

Average

Minimum

InconsistentProblem(high peak,low average)


Sample: “Telephony” Performance History

Single Frequency Time Window for 3 days from one return path

• Average telephony signal at 36 MHz varies consistently by time of day

• Indication of higher telephony usage times

7:00AM 11:00PM 7:00AM11:00PM


6MHz CPD


Signal clipping —RF ingress and impulse noise can cause signal clipping, or compression, in reverse plant active components. Excessive levels from in-home devices such as pay-per-view converters also can cause clipping. Clipping occurs in reverse amplifiers and optical equipment.



Ingress

75 – 90% of ingress originates in the subscriber’s home

To minimize the effects of ingress, operate the subscriber terminals (modems & set-tops) near maximum transmit level


Non-linear mixing from a diode junction

– Corrosion (metal oxide build-up) in the coaxial portion of the HFC network

– Dissimilar metal contacts

– 4 main groups of metals• Magnesium and its alloys• Cadmium, Zinc, Aluminum and its alloys• Iron, Lead, Tin, & alloys (except stainless steel)• Copper, Chromium, Nickel, Silver, Gold, Platinum, Titanium,

Cobalt, Stainless Steel, and Graphite

Second and third order distortions

Common Path Distortion (A.K.A. CPD)


24 MHz

Common Path Distortion (A.K.A. CPD)

CPD distortions are spaced at 6 MHz apart from each other starting at 6 MHz


DOCSIS®Modem Carrier

Wide band noise

beyond 42 MHz diplex roll-off

24 Hour Performance History Max Hold Detail Graph

Diplex roll-off above 42 MHz


Thermal Noise and Laser Noise

Maintain a tight control of reverse RF signal levels – Laser drive level too high

• causes excessive laser clipping– Laser drive level too low

• reduces C/N and C/I ratios

Reverse levels must be held to a relatively narrow ‘window’ in order to guarantee that they fall comfortably between a lower limit (imposed by the noise floor) and a higher limit (set by laser clipping noise)


Micro-reflections

Damaged or missing end-of-line terminators Damaged or missing chassis terminators on directional coupler, splitter, or multiple-output amplifier

unused ports Loose center conductor seizure screws Unused tap ports not terminated; this is especially critical on low value taps, but all unused tap

ports should be terminated with 75-ohm terminations (locking terminators without resistors or stingers do not terminate the tap port)

Poor isolation in splitters, taps and directional couplers Unused customer premises splitter and directional coupler ports not terminated Use of so-called self-terminating taps at feeder ends-of-line; these are the equivalent of splitters,

and do not terminate the feeder cable unless all tap ports are terminated Kinked or damaged cable (includes cracked cable, which causes a reflection and ingress) Defective or damaged actives or passives (water-damaged, water-filled, cold solder joint, corrosion,

loose circuit board screws, etc.) Cable-ready TVs and VCRs connected directly to the drop (return loss on most cable-ready devices

is poor) Some traps and filters have been found to have poor return loss in the upstream, especially those

used for data-only service

Causes:

RON HRANAC

[email protected]


Why Go Digital?

Efficiency

– Source signals are digital

• Standard and High Definition TV (SDTV, HDTV)

– High Speed Data and Digital Video is more efficient than analog

• Transmit equivalent of 6 to 10 analog channels (VCR quality) or 2 HDTV programs over one 6 MHz bandwidth

Quality

– Better Picture and Sound Quality

– Less Susceptible to noise

• Error detection and correction is possible

Flexibility

– Data-casting easily multiplexed into digital signal

– Higher Data Security


Generate Digital

What is Digital?

Source and Destination is digital data– Assign unique patterns of 1’s and 0’s

Transmission path is via an analog QAM carrier – Choice of modulation is the one that optimizes bandwidth

(data versus frequency ‘space’) and resiliency to noise

00 01 10 11 00 01 10 11

Receive Digital

QAM Analog Carrier


QAM combines QPSK and AM modulation. QAM uses 2 channels of information each carrying half

the data.

10 11

AM Modulator

AM Modulator

Bit StreamCarrier

Carrier + 90°

Combiner

I Channel

Q Channel

Quadrature Amplitude Modulation (QAM)


Vector Sum of I and Q Channels

Combining 2 carriers 90° of out of phase results in a carrier with amplitude and phase modulation

4 Levels of I

Channel

+ =

00

00

01 10 11

01

10

11

4 Levels of Q

Channel

..10 11..Data Stream

..10 11..

16 QAM

4 Levels of Q

4 Levels of I


Constellations, Symbols and Digital Bits

16 QAM

Each “dot” on constellation represents a unique symbol

Each unique symbol represents unique digital bits

Digital data is parsed into data lengths that encode the symbol waveform

4 Levels of Q Channel

4 L

evel

s of

I

Ch

ann

el


64 QAM and 256 QAM

64 QAM has 8 levels of I and 8 levels of Q making 64 possible locations for the carrier

256 QAM has 16 levels of I and 16 levels of Q making 256 possible locations for the carrier


16 L

evel

s of

I

Ch

ann

el


8 L

evel

s of

I

Ch

ann

el

64 QAM 256 QAM


QAM and CATV

16 QAM is part of the DOCSIS® 1.0/1.1 upstream specifications

64 QAM and 256 QAM is used for both digital video and DOCSIS downstream, allowing more digital data transmission using the same 6 MHz bandwidth

– Transmit equivalent of 10 to 12 analog channels (standard definition) or 2 HDTV programs over one 6 MHz bandwidth

Standard for data over Cable

– Cable systems provide higher signal to noise ratios than over-the-air transmission. A well designed and maintained cable plant meets these QAM signal to noise requirements


QAM Data Capacity (Annex B)

16 QAM(Upstream)

64 QAM(Downstream)

256 QAM(Downstream)

Symbol Rate (Msps)

2.560 (@ 3.20 MHz)

5.0569(@ 6 MHz)

5.3605(@ 6 MHz)

Bits per symbol

4 6 8

Channel Data Rate (Mbps)

10.24 30.3417 42.8843

Information bit rate(Mbps)

9.0 26.9704 38.8107

Overhead 12.11% 11.11% 9.5%


Constellation Display

The constellation is a visual representation of the I and Q plots


Effects of Noise and Interference

Ideal Locations

Noise and Interference moves the carrier away from its ideal location causing a spreading of the cluster of dots.


Modulation Error Ratio (MER)

Analogous to S/N or C/N A measure of how tightly symbols are recorded

with respect to desired symbol location

MER(dB) = 20 x log RMS error magnitude average symbol magnitude

Good MER– 64 QAM: 28 dB MER– 256 QAM: 32 dB MER

RMS errormagnitude

Average symbol

magnitude


Constellation Zoom

Zooming in on the constellation you can see how the carrier spread and how close it came to the decision boundaries.

Decision Boundaries


Digital Content – Analog Carrier

The Carrier, by the way, is ANALOG Modulation

Analog Content – Analog Carrier


PathTrak QAM Analyzer View – Good Node

QPSK & 16QAM Constellation

MER & Level Graphed over Time

MER & LevelAvg/Max/Min

Live MER, Level & Symbol Count


Interference causing intermittent low MER

Interference easily visible in 16 QAM

constellation


constellation


constellation

PathTrak QAM Analyzer View – Bad Node


“Back to the Basics” Troubleshooting

Majority of problems are basic physical layer issues Check AC power Most of the test strategy remains the same – divide

and conquer technique Check forward and return RF levels, analog and digital Check forward / reverse ingress Do a visual inspection of connectors / passives Replace questionable connectors / passives Tighten F-connectors per your company’s installation

policy– Be very careful not to over tighten connectors on CPE (TVs,

VCRs, converters etc.) and crack or damage input RFI integrity

System Sweep and Ingress Suppression

Why sweep?

Why suppress Ingress?


• Less manpower needed

• Sweeping can reduce the number of service calls

VOD not working

Internet not workingChannel 12 video

problemsCracked hardline

found with SWEEP

WHY SWEEP?


Success rate of finding and fixing the following problems using:– Signal Levels– TILT– Gain / Loss– Suck-outs (notches)– C/N– HUM– CTB/CSO Intermodulation– CPD - Forward and Reverse– Reverse Ingress– BER / MER– Reflections / Standing waves

What faults cause CATV signals to fail ?(80-90% of the time, the same faults…)

Source: Research 11/97-2/98 Market survey with 200 US and European CATV operators

21% Reverse Ingress

23% Signal Level Meters

11% BER Digital Analyzers

72% Forward & Reverse Sweep

5% Spectrum Analyzers

7% Visual TV-picture inspection


CATV amplifiers have a trade-off between noise and distortion performance

Tightly controlling frequency response provides the best compromise between noise and distortion.

WHY SWEEP?


Segmented Error Budgets

Test Critaria Measurement Goal Start Seeing Degradation on Call

Quality

Delay (1-way) < 100 ms > 150 ms

Jitter < 5 ms > 15 msService Level Test Packet Loss < 0.5% > 2%

R-Value > 80 < 70

MOS > 4 < 3

MER 30dB(64), 33dB (256) 25dB(64), 28dB(256)

RF PRE-FEC BER 1.00E-09 1.00E-07At Home Rx - Level -5~+5 dBmV <-10dBmV or >+10dBmV

Tx - Level 35 ~45 dBmV < 30dBmV or >50dBmVMER 32dB(64), 35dB (256) 28 dB(64), 31dB(256)

RF PRE-FEC BER 1.00E-09 1.00E-07At Node Freq Response < 4dB > 5dB

Upstream SNR >35dB <25dB

CMTS CMTS Loading <50% >80%


Sweep Verifies Construction Quality

• Sweep can find craftsmanship or component problems

that aren’t revealed with other tests

• Damaged cable

• Poor connectorization

• Amplifier RF response throughout its frequency range

• Gain

• Slope

• Loose seizure screws, module hardware…….


System’s ability properly to transmit signals from headend to subscriber throughout the designed frequency range

“Sweep” tests verify performance to design specifications Expected Results: N/2 + X = max flatness variation

• where n = number of amplifiers in cascade• where x = best case flatness figure

Typical Flattness formulas are: n/10+1 old systems with 30 amp cascade 400 MHz Bandwidth N/2+2 new systems with and 5 to 7 amp cascade 750 MHz

Bandwidth

Frequency Response Definition


Test Probes

Will always be bi-directional unless they are in series with the circuit

Higher loss probes provide less of an impedance mismatch, but lower levels

F-to-Housing adapters cause severe standing waves because of;– Bad grounding

– RF power splitting

– Impedance mismatch

Be careful with in-line pads while probing seizure screws– Not usually dc blocked


Sweep Response of a Splitter

RFIN

RF OUT

INPUT

OUTPUT


100 ft of RG-59 cable

RFIN

RF OUT

INPUT

OUTPUT


Sweep Response of 17dB Tap

Tap Port

Tap RF

Out


Sweep Response of a Amplifier

Amplifier Forward

20dB

Amplifier Return

12dB

RF in

RF in RF out

RF out


A Sweep Finds Problems That Signal Level Measurements Miss

Standing Waves

Roll off at band edges

Misalignment


Balancing AmplifiersBalancing amplifiers using tilt

No TerminationLose Face Plate, or crack cable

shield

Node Reference Signal Sweep response with a Resonant FrequencyAbsorption

Sweep response with standing waves

Headend


Step 1) Forward & Reverse SweepWHY SWEEP?

Headend

No TerminationLose Face Plate, or crack cable

shield

Node Reference Signal Sweep response with a Resonant FrequencyAbsorption

Sweep response with standing waves

D = 492*Vp/F

F


Types of Sweep

Sweepless Sweep Forward Sweep Return Sweep


“Sweepless” Sweep Method

Developed by Wavetek in the late 1980s Compares headend levels to system test point

levels Totally non-interfering (no sweep injection signal) Relatively inexpensive (no headend unit) Normal level variations in headed signals cause

loss of valid reference information Blank spectrum not tested


‘Sweepless’ Sweep


Sweepless Sweep with Channel drop out


Sweep with Transmitter

Sweep transmitter and headend monitor Constantly monitors video, audio, and digital carriers plus

sweep insertion points Transmits any level variations to the SDA-5500 or DSAM

6000 on a telemetry carrier to update the reference– Keeps receiver up to date on headend levels


Typical Forward Sweep Response

Fiber Node Line ExtenderEnd of Line Tap


Bench Sweep Amplifiers

Verify old modules


Beware of Taps

Port 1 thru 8 not terminated Port 1 thru 8 terminated


System Problems

55.25 MHz 745.25 MHz

Low end roll off High end roll off

Resonant Frequencyabsorption


3 dB /100 MHz /

Signature

System Problem

System Problem vs. Signature


Headend to Tap

Typical system not swept or balanced for 6 months

HH

LL

SDA-5500 - Headend unit

FREQFREQ

CHANCHAN

ENTERENTER

FCNFCNCLEARCLEAR

helphelp

statusstatus

alphaalpha

lightlight

abcabc defdef ghighi

jkljkl mnomno pqrpqr

stustu vwxvwx yzyz

spacespace +/-+/-

11 22 33

44 55 66

77 88 99

00

xx

..

FILEFILE

AUTOAUTO

SETUPSETUP

TILTTILT SCANSCANLEVELLEVEL

C/NC/N HUMHUM MODMOD

SWEEPSWEEP

SPECTSPECT

PRINTPRINT

System Sweep Transmitter 3SRSystem Sweep Transmitter 3SRSystem Sweep Transmitter 3SRSystem Sweep Transmitter 3SRStealth SweepStealth SweepStealth SweepStealth Sweep

Ampifiers not balanced

Cracked Hardline

FCC Proof Failure

Customer Complaints

Noisy pictures!

HD Tiling


Headend to Tap

Typical system after Sweep and Balance

HH

LL


FREQFREQ

CHANCHAN

ENTERENTER

FCNFCNCLEARCLEAR

helphelp

statusstatus

alphaalpha

lightlight



stustu vwxvwx yzyz

spacespace +/-+/-

11 22 33

44 55 66

77 88 99

00

xx

..

FILEFILE

AUTOAUTO

SETUPSETUP



SWEEPSWEEP

SPECTSPECT

PRINTPRINT


Ampifiers balanced

Hardline good Condition

FCC Proof PASS!

Customers Satisfied!


Analog Integrity is Still Paramount, Supplemented by Digital Measurements

Majority of “digital” issues involve basic analog maintenance of the RF plant– Levels, including network tilt, must be optimized– RF distortions such as CSO and CTB can affect QAM carriers– Managing hum has been shown to improve QAM carrier quality– Carrier-to-noise and signal-to-noise (MER on QAM channels)– BER and DQI for intermittent impairments– Ingress management


Goal

The objective in reverse path alignment is to maintain unity gain with constant inputs and minimize noise and ingress.

Set all optical receivers in the headend to same output level and ideally the same noise floor to optimize C/N ratio.– The reverse path noise is the summation of all noise

from all the amplifiers in the reverse path.


Sweep Reference Considerations

Typically the node is used for the reference Use test probe designed for node/amp It’s a good engineering practice to store a new

reference each day Establish reference points to simplify ongoing

maintenance (sweep file overlay) Need to know amps hidden losses in return

path (Block diagrams / Schematics) Need to know where to inject sweep pulses and

the recommended injection levels


Optimizing the Node

Activation and maintenanceof the trunk network bySDA-5000 + SDA-OPT1 or SDA-4040D

Activation and maintenanceof optical nodes byDSAM 6000 with Reverse Sweep

Reverse-pathoptical receivers

HH

LL

ForwardLaser

Headend


FREQFREQ

CHANCHAN

ENTERENTER

FCNFCNCLEARCLEAR

helphelp

statusstatus

alphaalpha

lightlight



stustu vwxvwx yzyz

spacespace +/-+/-

11 22 33

44 55 66

77 88 99

00

xx

..

FILEFILE

AUTOAUTO

SETUPSETUP



SWEEPSWEEP

SPECTSPECT

PRINTPRINT



Rev

erse

Co

mb

iner

X dBmV

FREQ

CHAN

ENTER

FCNCLEAR

help

status

alpha

light

abc def ghi

jkl mno pqr

stu vwx yz

space +/-

1 2 3

4 5 6

7 8 9

0x

.

FILE

AUTO

SETUP

TILT SCANLEVEL

C/N HUM MOD

SWEEP

SPECT

PRINT

System Sweep Transmitter 3SRSystem Sweep Transmitter 3SR Stealth SweepStealth Sweep

Pad input of the SDA-5510 for 0 dBmV

NODE

NODE

NODE

NODE

Optical Receiver

Optical Receiver

Optical Receiver

Optical Receiver

All Return Path RF signal levels must be set to same output “X” level at the optical receiver in the headend or hubsite with the same “X” level input at the node.

X dBmV

Return Path “X” LEVEL


Rev

erse

Co

mb

iner

X dBmV

FREQ

CHAN

ENTER

FCNCLEAR

help

status

alpha

light

abc def ghi

jkl mno pqr

stu vwx yz

space +/-

1 2 3

4 5 6

7 8 9

0x

.

FILE

AUTO

SETUP

TILT SCANLEVEL

C/N HUM MOD

SWEEP

SPECT

PRINT



NODE

NODE

NODE

NODE

Optical Receiver

Optical Receiver

Optical Receiver

Optical Receiver


X dBmV

X dBmVX dBmV



Rev

erse

Co

mb

iner

X dBmV

FREQ

CHAN

ENTER

FCNCLEAR

help

status

alpha

light

abc def ghi

jkl mno pqr

stu vwx yz

space +/-

1 2 3

4 5 6

7 8 9

0x

.

FILE

AUTO

SETUP

TILT SCANLEVEL

C/N HUM MOD

SWEEP

SPECT

PRINT



NODE

NODE

NODE

NODE

Optical Receiver

Optical Receiver

Optical Receiver

Optical Receiver

X dBmV

X dBmV


X dBmV

X dBmV

X dBmV





Rev

erse

Co

mb

iner

X dBmVX dBmV

FREQ

CHAN

ENTER

FCNCLEAR

help

status

alpha

light

abc def ghi

jkl mno pqr

stu vwx yz

space +/-

1 2 3

4 5 6

7 8 9

0x

.

FILE

AUTO

SETUP

TILT SCANLEVEL

C/N HUM MOD

SWEEP

SPECT

PRINT



NODE

NODE

NODE

NODE

Optical Receiver

Optical Receiver

Optical Receiver

Optical Receiver

X dBmV

X dBmV

X dBmV

X dBmV

X dBmV

X dBmV


Reverse Noise Floor

All Return noise floor levels should be maintained to supply approximately “X level minus 40 dB” going into the node.

Rev

erse

Co

mb

iner

X - 40 dBX - 40 dB

FREQ

CHAN

ENTER

FCNCLEAR

help

status

alpha

light

abc def ghi

jkl mno pqr

stu vwx yz

space +/-

1 2 3

4 5 6

7 8 9

0x

.

FILE

AUTO

SETUP

TILT SCANLEVEL

C/N HUM MOD

SWEEP

SPECT

PRINT


Return Telemetry must have at least a 20 dB SNR

NODE

NODE

NODE

NODE

Optical Receiver

Optical Receiver

Optical Receiver

Optical Receiver

X - 40 dB

X - 40 dB

X - 40 dB

X - 40 dB

X - 40 dB

X - 40 dB

Desired noise floors into node


Choose operating levels that maximize the distortion performance of your return path

Get all the information that you can on your nodes and amps from your manufacturer

Create a sweep procedure for your system– make up a chart showing injection levels at each

test point

ALIGNING THE RETURN PATH


ALIGNING THE RETURN PATH


Test Point Compensation

Graphical user interface

Store & recall of test point setups


User Interface: Forward Sweep

Raw Forward Sweep

Reference the Sweep Trace

Save the Reference name

Referenced Sweep Trace

Save the File for Records

Choose & Save the File name

Troubleshoot or Move to next device in the line


User Interface: Reverse Sweep

Raw Reverse Sweep

Reference the Sweep Trace

Save the Reference name

Referenced Reverse Sweep

Save the File for Records

Choose & Save the File name

Troubleshoot or Move to next device in the line


User Interface: Test Point Compensation

Test Point Comp menu can be accessed two ways:•Settings Hotkey in Sweep Measurement•Shift+4 on the keypad at any time

List of current TPC Files

Create a new TPC file

Name and save the TP device

Edit new TPC file

Specify TP device loses

Pick Reverse Tel & Insertion levels

Forward summary specs

Reverse Summary Specs

TPC now active on all tests


User Interface: Markers and Zooming

Go to View Menu

Move Markersto desired locations

Go to Zoom

New Frequency Range


User Interface: Sweep Settings

SelectSettings Tab

Sweep Settings

Turning on Tilt Compensation activates the Tilt settings

For bidirectional test points set the Reverse Sweep Port to Port 1For directional test points set it to Port 2 and attach the reverse test point to port 2 and the forward test point to port 1


User Interface: Telemetry Settings

SelectSettings Tab

Telemetry Frequency

If using an SDA-5500 headend unit only set the reverse Sweep to Single UserIf also using a SDA-5510 select Multi User for reverse Sweep

Set the telemetry of the SDA-5500 headend unit and SDA-5510 (if available)

PathTrak’sField ViewTelemetry


Sweeping Out

Connect to Input Test Point on Node

NODE

X dBmV

Telemetry = X dBmV

The sweep and alignment procedure for both the forward and return path starts at the node and then moves toward the end of line


Sweeping Out

X dBmV

Maintain unity gain with constant inputSet TP Loss as required

NODE

X dBmV

Telemetry = X dBmV

Connect to Input of First Reverse Amp


X dBmV


X dBmV

NODE

Sweeping Out

X dBmV

Telemetry = X dBmV



X dBmV


X dBmV

X dBmV

NODE

Sweeping Out

X dBmV

Telemetry = X dBmV



X dBmV


X dBmV

X dBmV

X dBmV

NODE

Sweeping Out

X dBmV

Telemetry = X dBmV



X dBmV


X dBmV

X dBmV

X dBmV X dBmV

NODE

Sweeping Out

X dBmV

Telemetry = X dBmV



Damaged or missing end-of-line terminators

Damaged or missing chassis terminators on directional coupler, splitter or multiple-output amplifier unused ports

Loose center conductor seizure screws

Unused tap ports not terminated. This is especially critical on lower value taps

Unused drop passive ports not terminated

Use of so-called self-terminating taps (4 dB two port; 8 dB four port and 10/11 dB eight port) at feeder ends-of-line. Such taps are splitters, and do not terminate the line unless all F ports are properly terminated

Common problems typically identified in outside plant


Kinked or damaged cable (including cracked cable, which causes a reflection and ingress).

Defective or damaged actives or passives (water-damaged, water-filled, cold solder joint, corrosion, loose circuit-board screws, etc.).

Cable-ready TVs and VCRs connected directly to the drop. (Return loss on most cable-ready devices is poor.)

Some traps and filters have been found to have poor return loss in the upstream, especially those used for data-only service.

Common problems typically identified in outside plant


Intermittent Connections

Poor craftsmanship on connectors

Loose center seizure screws & fiber connectors

Radial cracks in hard-line coaxial cable

Cold solder joints

Bad accessories


The Situation

Can’t justify taking the system down to troubleshoot Unacceptable to the subscribers who will;

– Lose communication

– Get a slower throughput

– Have periodic “clicking” in their telephone calls

To be non-intrusive we must;

– Understand test points

– Apply new procedures and applications

– Learn new troubleshooting techniques


Typical Problem Areas

Taps– Most ingress comes from houses with tap values of

17 dB or less

House Wiring– Drop Cable & F Connectors are approximately ~95%

of Problem

Amplifiers, hard line cable and the rest of the system are a small percentage of the problem if a proper leakage maintenance program is performed.


8 Port23 dB

tapThis would be a DC-12

The splitter network = ~11 dB of loss

Taps

Taps are a combination of a DC and a splitter network

Taps give an actual representation of what the subscriber is seeing and transmitting in to

Points to remember;– Lower valued taps equal more

through loss


Input Output

Testing at the Seizure Screws

If the problem is at the Forward Output, continue on

If the problem is at the Forward Input and not the Forward Output, then the problem is from one of the drops

Spring loaded seizure screw probes create a good ground and quick connect without causing outages

Forward Path

Return Path


Input Output

Testing at the Seizure Screws

Use a 20 db pad with AC block when using spring loaded seizure screw probes

Forward Path

Return Path


4 Port Tap

Probe the seizure screw for ingress

Taps are made up of a Directional Coupler and Splitters

Disconnect one drop at a time to determine the point of entry

-60

-50

-40

-30

-20

-10

0

10

20

30

40

Center: 25.000 MHzSpan: 40.000 MHzRBW: 300 KHz VBW: 100 KHz Dwell: 400 µS

In-Band Power 10.393 dBmV

-60

-50

-40

-30

-20

-10

0

10

20

30

40




Return Path

Taps - Probe the Seizure Screws for Ingress & CPD

If the problem is at the FWD Input and not the FWD Output, then the problem is likely from one of the dropsIf the problem is at

the FWD Output of tap, continue on towards end of line Forward Path

Disconnect one drop at a time to determine the point of entry


Electrical Impulse Noise from One House

-60

-50

-40

-30

-20

-10

0

10

20

30

40



-60

-50

-40

-30

-20

-10

0

10

20

30

40



•Reverse Spectrum shot at customer's drop


PathTrak Field View option combined with JDSU meters provides a complete “Find & Fix” field troubleshooting solution

• PathTrak Field View option on SDA and DSAM platform enables techs to greatly reduce MTTR (Mean Time to Repair), which increases customer satisfaction and loyalty

• PathTrak Field View option for DSAM provides a programmable CW carrier to aid in troubleshooting return problems

• Both SDA and DSAM have low pass filter for troubleshooting bi-directional test points

PathTrak™ Field View Option


NODE

Tracking Down Ingress and CPD


RBWSettings

Live Spectrum Analysis – RBW Setting


300kHz RBW

(Resolution Bandwidth setting)

+19.61 dBmV



1,000kHz RBW


+25.95 dBmV




30kHz RBW


+11.31 dBmV


Quick and Easy Spectrum Scan

View from 4 to 110 MHz spectrum with programmable pass/fail limits

Spectrum view with adjustable marker and zoom function

Selectable peak hold Store in work folder Standard feature on DSAM

Platform


FM Band IngressFM Band Ingress


eMTA-CABLE MODEM

7 dB TAP

Drop Cable

High Pass Filter

GROUND BLOCK

3-WaySplitter

DIGITAL SET-TOP

House

2-Way Amplifier

Testing the RF Network

VoIP

OLDER TV SET

Return Equalizer

ONLINE GAMING

WIRELESS LAPTOP

COMPUTOR

ETHERNET

Disconnect drop from tap and check for ingress

coming from customer’s home wiring

INGRESS SPECTRUM MEASUREMENTS

If ingress is detected, terminate other end of

drop and scan spectrum again for ingress


Troubleshooting is “Back to the Basics”

Majority of problems are basic physical layer issues Most of the tests remain the same Check power Check forward levels, analog and digital Check forward / reverse ingress Do a visual check of connectors / passives Replace questionable connectors / passives Tighten F-connectors per your company’s installation

policy– Be very careful not to over tighten connectors on CPE (TVs,

VCRs, converters etc.) and crack or damage input RFI integrity

Line Conditioning and Return Path Equalization

Why should you worry about return attenuation?


Level Control Scheme

Reversereceiver Node

Subscriberterminal

RF distribution

Servicesplitter

Nodecombiner

Digital servicereceiver &

demod.

Optical link

level control

Leve

l

Frequency

Leve

l

Frequency

Target levelinto laser

Target levelinto receiver


Optimizing (Conditioning) the Reverse Path

Adding reverse path attenuation -– enables flexible, more cost efficient design– increases C/N performance of communicating devices– reduces dynamic range of communication devices– reduces opportunities for reverse laser clipping– affords a ‘more forgiving’ network set-up during reverse

balance and alignment


Step Attenuators

Low value taps produce the majority of ingress and trouble calls within a typical HFC network. This is due to the lack of sufficient reverse attenuation found in higher-value taps. Applied directly to the tap port, Step Attenuators provide unity gain with all cable modems and other critical reverse transmission products like digital voice and high-speed Internet.

40 MHz

54 MHz

5 MHz

-12 dB

-1.3 dB


Reverse ‘Window’

Problem: Reverse window can exceed dynamic range of terminals

23 20 17 11 8

Forward levels:45/35 dBmV

Terminal

NID

Terminal

NID

Required reverse input level:22 dBmV

55 dBmV 41 dBmV

Terminal reverse 'window':55 - 41 = 14 dB

-10 dB -3 dB

In red: required tap port reverse level45.0 38.0


Reduced Reverse ‘Window’

Same area, ‘NID’ design standardized – reverse terminal ‘window’ improved by 7 dB

23 20 17 11 8


Terminal

NID

Terminal

NID

Required reverse input level:22 dBmV

55 dBmV 48 dBmV

55 - 48 = 7 dB

-10 dB -10 dB

In red: required tap port reverse level45.0 38.0

Terminal reverse 'window'


Reverse Tap Port ‘Window’- High Forward Levels, LEQ w/o RC -

Reverse ‘Window’ of required tap port levels: 44.9 - 31.2 = 13.7 dB

29 26 23 20


17

14 8

11 8132' 110' 110' 120' 110' 110'

132' 120'

Required Reverse Level @ Amplifier Input Port: 15 dBmV

44.0 43.2 41.0 39.1 35.2 31.2

43.3 39.4

44.9

In red: required tap port reverse level

DC-12


Reverse Tap Port ‘Window’- High Forward Levels, Using LEQ/RC -

Reverse ‘Window’ narrowed from 13.7 to: 44.9 - 39.1 = 5.8 dB

29 26 23 20


17

14 8

11 8132' 110' 110' 120' 110' 110'

132' 120'

Required Reverse Level @Amplifier Input Port: 15 dBmV

44.0 43.2 41.0 39.1 44.2 40.2

43.3 39.4

44.99 dB reversepad installed

In blue: previous reverse level required

35.2 31.2

DC-12


Reverse Tap Port ‘Window’- Low Density, LEQ w/o RC -

Reverse ‘Window”range of required tap port levels: 44.0 - 25.5 = 18.5 dB

29


1,560'

Required reverselevel: 15 dBmV

44.0 25.5

4


Reverse Tap Port ‘Window’- Low Density, Using LEQ/RC -

Reverse ‘Window’ narrowed from 18.5 to: 44.0 - 40.5 = 4.5 dB

29


1,560'

Required reverselevel: 15 dBmV

44.0 40.5

4

In blue: previous reverse level required

25.5

15 dB reversepad installed


Noise Floor Levels

Be careful with spectrum analyzer level readings

The level is based off the RBW setting and will be very different from one setting to another

A -20 dBmV noise floor with 30 kHz RBW is really 1.2 dBmV in a 4 MHz bandwidth

That’s why measurements with no point of reference are worthless

At least if there’s a reference carrier present, you can make a relative measurement


Severe Transient Hum Modulation

The RF choke can saturate with too much current draw and cause the ferrite material to break down

Same thing can happen in customer installed passives

Notice that this looks a lot like CPD


Correct pin length,Properly tightened

Pin length too short

Center Pin/Seizure Screws

Typical connector problems These may result in suckouts or roll off


Pin length too long

Overtightened seizure screwDamaged pin


This may also hamper the “seating” of the RF module


Pin tightened before turningconnector into housing

May result in a broken or twisted pin inside the connector


• A more typical result is the pin gets pushed back into the connector instead of pushing past the seizure screw

• Happens a lot to housing terminators


AfterBefore

Loose Fiber Connector

SC connector not pushed in all the way


Fiber Connectors Are Everywhere

Fiber optic connectors are common throughout the network, and they give you the power to add, drop, move and change the network.

Buildings

Multi-home UnitsResidential

Head End

Local Convergence Point

Network Access Points

Feeder Cables

Distribution Cables

Coaxial Network


Types of Contamination

A fiber end face should be free of any contamination or defects, as shown below:

Common types of contamination and defects include the following:

Dirt Oil Pits & Chips Scratches

SINGLEMODE FIBER


Where is it? – Everywhere

Airborne, hands, clothing, bulkhead adapter, dust caps, test equipment, etc.

The average dust particle is 2–5µ, which is not visible to the human eye.

A single spec of dust can be a major problem when embedded on or near the fiber core.

Even a brand new connector can be dirty. Dust caps protect the fiber end face, but can also be a source of contamination.

Fiber inspection microscopes give you a clear picture of the problems you are facing.

Your biggest problem is right in front of you… you just can’t see it!

DIRT IS EVERYWHERE!


Where is it? – Proliferation of Dirt

There are a number of different sources where dirt and other particles

can contaminate the fiber.

Test Equipment

Dust Caps

Bulkheads

People

Environment

Connectors and ports on test equipment are mated frequently and are highly likely to become contaminated. Once contaminated, this equipment will often cross-contaminate the network connectors and ports being tested.

Inspecting and cleaning test ports and leads before testing network connectors prevents cross-contamination.


Conclusion

If we want our telecommunications networks to be as reliable/available as the telephony business at 99.98%, we must;– Stay up with technology– Have contingency plans for everything– Train our employees– Utilize equipment that will quickly characterize and separate real

problems from insignificant events– Be Proactive instead of Reactive!


Thank You !Mark Ortel

Sales Support Engineer

Cable Networks Divisionwww.jdsu.com

SCTE Chapter

sweep overview mark ortel sales support eng. © 2005 jdsu. all rights reserved.jdsu confidential...

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