JDSU Presents The Cause and Effects of Bonding and Grounding on xdsl IPTV Services February 12 th, 2009

Size: px

Start display at page:

Download "JDSU Presents The Cause and Effects of Bonding and Grounding on xdsl IPTV Services February 12 th, 2009"

Avis Tucker
6 years ago
Views:

1 JDSU Presents The Cause and Effects of Bonding and Grounding on xdsl IPTV Services February 12 th, 2009 Jeff Harmon Account Manager Western Region Triple Play, Data/IP Analysis Solutions Office: Mobile:

2 IPTV Service Offering over DSL Services As the Service Provider of IPTV Services What s are your customers expectations? If you can t meet your customer s expectations what s at stake? You ve qualified your copper loop for xdsl loop You ve tested for AC/DC Current and Resistance Measured the pair for length Measure Longitudinal Balance Performed a TDR to check for bridetaps and other interferers Checked for load coils However, your customer is still complaining of tiling on their TV s and they re very dissatisfied with their service It s going on the second or third dispatch and the problems still exist Wideband Noise 2

3 Wideband Noise Definition Wideband noise is defined as noise in the spectrum of 25 khz to 2.5 MHz range. Ultra-wideband noise is defined as noise in the spectrum of 2.5 MHz to 30 MHz. DSL circuits carrying voice and high speed internet services are effected by WB noise on the line but those effects are often less noticeable than the effects of WB noise on circuits carrying IPTV signals. During a recent seminar a leading Cable TV authority discussed noise impairments that affect Cable TV signals within their Wideband RF frequencies. He noted that 500 khz -28MHz is the noisiest portion of the RF spectrum in the plant. He further stated the true service effecting noise is between 500 khz-15mhz. This is primarily due to AM radio, amateur radio, shortwave, and CB radios. 3

4 Causes of WB Noise The single biggest causes of WB Noise on your outside plant is Pair Balance and Bonding and Grounding problems The biggest problem with Bonding and Grounding schemes They were written for electrical protection rather than noise considerations With high frequency xdsl signals bonding and grounding schemes may have to change to support noise interferes and ingress 4

5 The Goal of Bonding Sheath Current is responsible for providing a magnetic field which helps to cancel at least part of what the power leads induce into the pairs. Most any type of signal/harmonic that is induced (ingress) into the pairs becomes noise To obtain maximum current in the sheath it is necessary to provide the least possible resistance in the bonding conductors and ground connections Using #6 stranded copper wire or copper braid attached to the cable sheath with compression clamps having a large contact area is your best choice for bonding conductors 5

6 The Goal of Proper Grounding As we look at Bonding and Grounding, Grounding is the most important of the two and also most difficult to achieve. The purpose of grounding is to make sure there is a good electrical connection from the cable sheath to the soil/earth. Herein lies the problem. The surface area of ground rod is really quite small The soil around the ground rod may be of high resistance because of the soil content and moisture. Always remember if a better path to ground presents itself, the sheath current will not flow to the ground rod but to the better path 6

7 Proper Grounding The best possible ground is the power company s MGN (multi-ground neutral), or a grounded neutral of a secondary power system, or a specially constructed grounding system Using the MGN is critical where the topology of the power lines change (transformer, capacitor bank, tap, drop, and direction change) as you need to get those locally coupled signals returned to their source return. If the locally sourced signals are not returned to their own source return they cannot be canceled as well as when they are returned to a distant return, thus you have noise ingress. Please don t think that ground rods serve no purpose as they do. Ground rods are there for personnel and plant protection in case of a lighting strike or power cross. 7

8 Bonding and Grounding Schemes to support IPTV If your DSL service has progressed to the point where you re going to offer IPTV services there s a chance your current bonding and grounding schemes may have to change. In order to eliminate WB noise from your cable plant to support IPTV services, it is imperative that every pole or pedestal be properly bonded and/or grounded with #6 stranded copper wire or copper braid attached to the cable sheath with compression clamps having a large contact area. It is also a good practice to seal every bond or ground with a dielectric sealant Always avoid using two different dissimilar metals for your bonding and grounding schemes as two dissimilar metals will invite the formation of corrosion. 8

9 Why is Bonding and Grounding more important than ever? xdsl evolution to higher frequency ranges for Triple Play Services - POTs to ADSL to VDSL - Higher sensitivity to interferers/poor balance Bridge Tap sensitivity increased Wider frequency band = More interference opportunities Technology ADSL ADSL2+ VDSL VDSL MHz 25kHz 1.1MHz 2.2MHz 12MHz Frequency 30MHz 9

10 OSP Local Loop Power Influence Power Lines Telephony Power Influence Noise level is determined by: Size of the magnetic field Distance from pair and the center of the field Distance both run parallel 10

11 Radio Frequency Interference (RFI) Caused when over-the-air radiofrequency signals (AM radio, amateur radio, short wave radio) couple into twisted-pair lines Pair balance and proper bonding and grounding is critical Noise power level Frequency 11

Testing ADSL 2+ line quality Using the Bits Per Tone Graph

graphs provide a graphical representation of the bits per

Dips sometimes represent areas where interference is

Large empty gaps in tones represent noise interferes that

12 Testing ADSL 2+ line quality Using the Bits Per Tone Graph to help identify noise interferes Graphical Results: The graphs provide a graphical representation of the bits per tone (BPT). Dips sometimes represent areas where interference is degrading the ADSL signal. Large empty gaps in tones represent noise interferes that have ingress into the line Tone 256 (1104kHz), Bits 14 Moving the Cursor to those dips or gaps will help to identify the affected frequencies. 12

13 Identifying WB Noise on your pair The two examples below show high wideband noise These two examples show good noise readings, though the -51 dbm reading is getting near to the top of the threshold. 13

14 Understanding the dbm and dbrn Scales Noise Thresholds can be measured with either a dbm or dbrn scale dbm measures absolute power 0 dbm equals 1 mw to the appropriate load dbr n measures db above reference noise: Reference noise 0 dbr n = -90 dbm Scale show the relationship between dbm and dbrn There is much confusions between these two scales 0 dbm 90 dbrn dbm or dBrn

Using a Spectral Analyzer The purpose of this test is to analyze wideband noise across the VDSL spectrum It is important to understand the information being displayed on the spectral noise graph.

15 Using a Spectral Analyzer The purpose of this test is to analyze wideband noise across the VDSL spectrum It is important to understand the information being displayed on the spectral noise graph. For VDSL circuits the noise floor should not exceed -100 dbm. The lower the noise floor on a VDSL circuits the better. 1. Often you can see the actual up and down stream VDSL signals on the spectral noise graph 2. The noise floor for a VDSL line should remain below -100 dbm. 15

16 VDSL Bonding and Grounding Trouble Good VDSL Sync levels however the customers IPTV signal is tiling Sync at Crossbox Sync at Customers NID Bonding problems cause of noise Bonding problems corrected -119 dbm noise floor 16

17 17

T-BERD /MTS-4000 Multiple Services Test Platform Copper Services Module

COMMUNICATIONS TEST & MEASUREMENT SOLUTIONS T-BERD /MTS-4000 Multiple Services Test Platform Copper Services Module Key Features Complete copper testing from POTS through full-spectrum VDSL/VDSL2 up to