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Wavetracking the leakage basics
By Ken Eckenroth
Vice President
Engineering Cable Leakage Technologies

After five years in the signal leakage business, something has become very obvious: the need for a routine. This is especially true now during this explosion of new converging technology. However, routine must be tempered or open ended to respond to the influx of new ideas into this pot of accumulated knowledge. The purpose of this article is to define a routine placing emphasis on default values. I also will discuss some of the advanced logic that can be used to optimize performance.

Coherent spectral analysis
Before we go any further, let’s take a look at the concept of signal leakage. The process in its raw form is in a state of incoherence. (See Figure 1.) Picture for a moment two baseballs being pitched simultaneously toward home plate and first base. It’s not until the ball is caught at one of these places that it becomes reality. This creates a record of the interaction. Without a record, it’s the same thing as closing your eyes and pretending it’s not there. If the ball is caught at both places, a second record is created, reinforcing the first record. The major variable here is the time between the two measurements. The less time, the better mathematical description with lower various possibilities.

A shotgun or random approach to leakage is similar to balancing every other amplifier. The odds will sooner or later catch up to you. Remember, “Big Daddy” (150 mV/m and higher) is lurking. A street-by-street methodical ride-out is the very foundation of coherent spectral analysis (CSA). The goal of CSA is to minimize all variables. CSA is possible through math and computer logic.

fig 1

Math and computer logic may be dry and boring, but what it can do is anything but. More discussion of CSA will follow in another article. For now we will concentrate on the CSA aspects of the following:
1) Blind spots (contouring)
2) Standing waves (with longer search times)
3) Time between measurements
4) Atmospheric conditions
5) Proximity thresholds
6) Spike values (duration or dwell time)

With the previous ideas in mind, let’s take a look at the life of a fictional technician. His name is Stevie Vaughn and he works for R&B Cablevision in Dallas. Stevie has become a legend at R&B even though in the beginning he was overshadowed by his brother Jimmy. Hard work, perseverance and eagerness to learn were his trademarks making up for less seniority in the company.

Stevie remembers the day he first read Cable Leakage Technologies’ Wavetracker manual. He had just torn some ligaments in his knee. He couldn’t climb, but he could drive a vehicle. Full pay is a lot better than reduced Workman’s Comp pay. Plus R&B Cablevision likes having all their workforce available. So Stevie took the manual home. It wasn’t so bad giving up one night of guitar practice to read this manual. The next day Stevie was ready to establish a routine knowing the next quarter he would have a routine.

First he looked at the “tracker.cfg” file. The UTC time correction was set at 6, which is correct for daylight savings time in Dallas (Central Time zone). The default values for the distance keys (20, 40, 80 and 160 feet) work well for R&B Cablevision’s plant because it’s a mixture of backyard easement and street side cable. The threshold and spike values work pretty good too.

However, he makes these values higher and places them on a separate disk. He saves this disk for when he rides-out that neighborhood that has 20 year old cable and leaks like a sieve.

Everything looks good on the tracker.cfg file. The next thing to do is start the Deltawave GPS base station recording differential corrections. Stevie enjoys the increased 10 to 25 meter accuracy. That puts the line tech on the right street when he fixes the leak. Losing time on that is no different than losing time on tracking down a standing wave to its source.

fig 2

In the field
Stevie checks his vehicle for low air pressure, worn fan belts and good Wavetracker connections much like a pilot would do his careful preflight check (See Figure 2.) Stevie powers on the Wavetracker to begin the GPS lock-in period. The two to four minute lock-in (cold start) became part of the drive to the neighborhood ride-out. Stevie as learned that once a GPS locks in on a given day, the GPS has a full almanac of that day’s constellation and locking-in after lunch takes 30 seconds or less.

On the way to the neighborhood, Stevie stops at an area he knows is RF quiet. He sets the distance on the Wavetracker to 10 feet. Ambient noise should be 3 mV/m or less. Anything above this indicates a noisy RF problem somewhere from the vehicle and should be corrected before the ride-out begins.

After finishing the morning ride-out session, Stevie stops for lunch. He eats outside enjoying the nice weather. He remembers when the company made the decision not to do ride-outs in the rain. Several factors were weighed in this decision:
1) Safer and faster driving conditions.
2) The 90-day quarter allowed the time.
3) Removing the rain factor in the RF measurement.

Stevie can remember fixing an outage in the rain because he had to. He never saw a need to measure a leak in he rain. Doing the drive-out in dry weather made the atmospheric conditions of the ride-out more closely resemble the conditions of the measurement. Stevie thinks about how rain definitely affects the measurement. (It seems to dampen or quiet the leak.) But because of its refractive nature, it’s unpredictable. It is very similar to the in-phase/out-phase, additive/subtractive qualities of multipath. Some are a little higher, some a little lower. Even though they might average out, it’s always a good idea to minimize the variables if possible.

Stevie starts his afternoon ride-out session. He navigates the three-lane primary streets with ease hitting the 20 feet distance key for the first lane next to the street side cable. He switches to 40 feet as he moves to the third lane. Stevie hits the “L” flag key to mark some broken lashing wire possibly preventing an outage waiting to happen.

Stevie pulls into an older neighborhood with some chewed up alleys that produce many a flat tire. Stevie likes the company policy of only riding these alleys once out of the four quarters in a year. The 160 feet distance key effectively finds all the high level leaks and most of the low level leaks. Stevie gets a kick out of finding the low level leaks at a great distance. He remembers when he used to use a TV set to track low level ingress problems.

fig 3

Post ride-out
As the ride-out nears completion, it’s almost anticlimactic, so Stevie decides to use the flag keys to spell out a subliminal message for his boss. He finds a street heading east and spells “company truck for Stevie. ” At the end of the neighborhood ride out Stevie presses “E” to end the Wavetracker program.

Stevie arrives at the shop. This makes him think again about getting full pay because the usual data entry person is letting him process the data because of his injury. Stevie stops the Deltawave record process and inserts his ride-out disk. He converts (corrects) his data. He then exits the Deltawave program and enters the “Mapinfo” program. Stevie chooses the “RFLEVELS” file from the start-up file menu, knowing that this creates a digital blank page. He then chooses “Cableleak” from the applications menu, which initiates the Wavetracker software. Stevie whizzes through the menus happy that the DOS commands are batched and condensed into descriptive menus. Stevie chooses “import” and lets the PC color-code and frame that day’s ride-out.

Then he chooses “mapfiles” and adds the street layer by selecting the “TXDALLAS” county map Stevie then starts the “Leak Center” to pick the center of each cluster of leaks. Experience at this shows him that Big Daddy leaks (large red squares) splash out on neighboring streets. He also sees two low-level leaks (small yellow squares) out by themselves separated by quiet areas (small green squares) and knows to treat (Leak Center) these as separate leaks.

After tagging each cluster, Stevie hits escape and lets the PC take over. The results are refreshed on the screen. Stevie chooses output and prints three work orders. One work order is a list of the flags and their addresses that go to the construction department to get that cable relashed. The next two are for Jimmy the line tech. One is a tabular list of leaks with amplitude, distance symbol and address. (See Figure 3.) The second is a map output to staple to the first work order and assist in cross-reference for locating the leak. (See Figure 4.) Stevie thinks “Boy, Jimmy is lucky to have a brother like me printing both these maps for him.”

fig 4

Stevie remembers talking to a tech from a different system at a Society of Cable Television Engineers meeting. The tech said because he worked for a larger system with several line techs, the system used the “Assign Area” to give each leak an area code or map page number. When the work orders are printed, they are presorted to give to the various line techs in their assigned areas. This tech also told Stevie how the system exports its leak data to the cumulative leakage index (CLI) program “LES.” Stevie acknowledged the tech’s way of working his options but was happy with his stand-alone Wavetracker software.

Stevie knows that as soon as he’s finished with the raw data, he can dispose of it. He initiates the “Rename Files” command and chooses to rename only the two files that matter to him. He renames “RFLEVELS” to “3QTR93.” Everyday he can add to this growing list of processed data. He also renames the “SCRATCH” file, which represents the drive path he acquired that day, and appends it to a highlight file he names “ZZ3QTR93.” This is his permanent record of what has been done that quarter and can be copied to floppy disk for permanent storage. He now can dispose of that day’s ride-out by choosing the “Reset Data” command.

Once a year, the CLI certification must be performed. Stevie has this down pat. He renames the two files back to their original names. “3QTR93” is renamed “RFLEVELS” and “ZZ3QTR93” is renamed “SCRATCH.” Stevie then performs the “Distance” command to obtain the accumulated total miles of each day’s ride-out. Then with the returned work orders from the line tech, he has the corrected measured data to achieve his CLI numbers per the letter of the law.

He enters the “Post Ops” menu that gives him the following three options:
1) “Post Edit”, which allows him to correct he amplitude of any of the leaks.
2) “Post Add”, which allows him to add a leak if there were more out there.
3) “Post Delete”, which allows him to get rid of standing wave byproducts that were produced by one leak.

Once this is done, Stevie enters the “I3000” menu and sees the total miles that were driven. On the next screen, he enters his systems total strand miles of plant. He then chooses the geographic center of the city and the software calculates the CLI and asks Stevie if he wants to print a report. (See Figure 5.) Since Stevie figures the FCC probably wouldn’t take his word for it, he enters yes and prints supporting documentation to attach to his Form 320.

Stevie looks at the clock and sees it’s 4:45 p.m. There’s time enough to print a map showing directions to his home. He wants to give it to the new dispatcher so she can come over and hear the new guitar licks he’s been working on.

I think we can all see that Stevie Vaughn was someone that vowed he wouldn’t be swallowed by the cracks. God bless Stevie and the work ethic he represented. He inspires a lot of us to take it to the next level.

fig 5

Copyright © 2004 Cable Leakage Technologies. All Rights Reserved.

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