Shotgun or Rifle

What's in your Leakage Arsenal?

By Ken Eckenroth, Cable Leakage Technologies

Each season has its jobs. And whether it's winterizing the house, cleaning out the garage or shed in the spring, packing up for summer vacation, or getting ready for the opening of hunting season in the fall, these tasks all have their own checklists.

A hunting list, for example, might include a cleaned and oiled gun, a case of 12-gauge shells, proper chokes, camouflage, license and bug spray.

For cable operators, one field task comes around every quarter: monitoring essentially the entire plant for leakage exceeding Federal Communications Commission limits. Here's a list of leakage equipment that should be familiar to many technicians:

• Yearly calibrated RF leakage meter
• Quarter-wave monopole antenna cut to the correct length for the frequency being monitored
• Half-wave dipole for measuring leak before repair
• Calibrated test leak at office
• FCC Web site for the new electronic filing
• Driving gloves for hours of drive out

It's a routine job, maybe too routine. Every now and then, it's worth asking: "Why are we doing all of this? And is there anything else to say about getting the job done?"

FCC rules

As for the first question, it's the law, FCC law. Since 1985, cable operators must completely drive out their plant four times a year, logging all leaks 20 µV/m and above. Since 1990, we must conduct a driveout of at least 75 percent of the plant, and file a CLI report to the FCC showing all leaks 50 µV/m and above, indicating which leaks are repaired and their locations. As an alternative to the annual rideout, a flyover of the plant is permitted.

But even if it were not the law, wise cable operators would vigorously repair their leakage anyway. Ingress can wreak havoc on a system's return path and cause degraded signal quality in the downstream. It can also interfere with an operator's Internet performance, as well as completely disrupt a system's voice over Internet protocol (VoIP) service. With the 99.99 percent availability goal for voice, leakage and ingress mitigation areis? a necessity.

We are very familiar with the FCC rules for leakage. However, there is a lesser known but very important rule in section 76.614 that covers the cable regular monitoring. It states:

"A cable television operator transmitting carriers in the frequency bands of 108-137 and 225-400 MHz shall provide for a program of regular monitoring for signal leakage by substantially covering the plant every three months. The incorporation of this monitoring program into the daily activities of existing service personnel in the discharge of their normal duties will generally cover all portions of the system and will therefore meet this requirement."

Note the word "substantially." The FCC recommends that the technician vary his route a little from day to day. And they emphasize section 76.605(a) that states we must find all leaks 20 µV/m and above. The FCC considers numerous mitigating factors in deciding whether a system will receive a fine and how high they are. It is not a case of whether a technician finds cut cable and a large leak, but whether the system strives for overall diligence to signal leakage monitoring and leakage repair. This includes maintaining quarterly logs and doing yearly CLI.

This portion of the rules that allows service techs to perform leakage during their normal daily duties has profound strategic and economic implications, especially to those operators who are concerned with the bottom line and don't wish to leave anything lying on the table. So with that in mind, let's define the two approaches - shotgun and rifle - and look at how each impacts your quarterly leakage monitoring.

Rifle and shotgun

The "rifle method" is very common and used by several cable operators. It incorporates a street-by-street methodical approach to monitoring. It generally utilizes a dedicated leakage technician who picks a neighborhood to ride out each day, continuing until 100 percent of the plant is driven out. Or if a company wishes to ride out the entire system in a shorter period of time, it might use several technicians to knock it out quickly. The rifle name implies a specific target of methodically patrolling street by street.

The "shotgun method" incorporates most or all of the service and line technicians. Each tech has a leakage meter in his vehicle. He will make note of each leak 20 µV/m and above during his routine of normal service calls. The shotgun name implies a scattered pattern of coverage.

Each method has its pros and cons. The rifle method ensures complete coverage, but it uses additional and dedicated personnel. The shotgun method uses existing personnel at no additional cost, but the coverage may be incomplete. But that is just the tip of the iceberg in explaining why this method is in the minority.

There are more disadvantages to the shotgun approach. A manual shotgun method can produce duplicate leaks. Several techs may go down the same street and record the same leak. The shotgun method also is inefficient in locating the source of a leak. The tech has to back up and pull forward to peak out a leak, which also makes this approach somewhat unsafe. The leak may also be on a different street, and finding the leak will take more than a few minutes. This additional time is likely to make the tech late for his next service call, so the particular leak may well be abandoned because leakage detection is a secondary task under the shotgun approach. And finally, a tech doing a secondary task is likely to improperly estimate the correct value of the leak. A common mistake is to ignore leaks lower than 20 µV/m, when in reality the leak is much higher than what the meter reads. A leak from a home or back yard easement is much lower when measured at the street because of the inverse square law of RF propagation.

Global positioning

One solution to the challenges of both the shotgun and rifle manual methods of doing leakage is automated mapping and global positioning system (GPS) tracking software available to cable operators. This utilizes GPS tracking for the automated recording of the vehicle's location and the ambient RF level at each point of the driven path.

This hardware and software has been available since the early '90s for the rifle method. It is incredibly efficient at locating the source of a leak. There is no more driving back and forth to peak out a leak because all the data has been recorded. The peak is determined when the cluster of leaks is analyzed. There is also no more looking for leaks down the wrong street or alley because the software has a leak circle (radius) algorithm that gets larger per the amplitude of the leak and finds the location of the highest RF level. This is essential for large leaks that radiate out over several streets.

The new solutions to the shotgun method are just now being introduced. The reasons why the shotgun method was in the minority are being addressed so that the economic benefits of using existing personnel can be realized. The challenges of the shotgun method are:

• Duplicate leaks
• Inefficient searches
• Underestimated leak values

These three problems can be solved when you use automated GPS tracking for leakage. Each service tech has a leakage detector attached to a GPS system. During a tech's normal service routine, all events are being recorded and then uploaded to the analytical software. An intelligent leak radius is created for each leak location. This radius is then tagged as the area for that leak.

An exact address cannot be used for the leak because the RF event is recorded automatically by several techs with different times, speeds, antennas, directions and sometimes even different streets. These multiple recordings are all at different physical locations. A geographic leak radius is by far the most efficient way to keep tabs on an automated GPS leakage environment. Now that we have a geographic area, duplicate leaks can be ignored. And this continues until the leak is repaired and closed out. The inefficient searches are eliminated because the software can easily find the peak of the leak in a cluster of leaks.

That takes care of duplication and inefficiency. As for underestimating leak value, the user can input the correct range values. You do not want to accept a leak with its value based on a 10-foot reading. You need to have a multiplier to apply to the leak so it is the correct distance from the vehicle on the street to the house or the pole line.

Combinations

There will be situations where the rifle and shotgun method will be combined. This combination has precedent in leakage, specifically in the several cable operators that combine a yearly CLI flyover with along with their ground-based quarterly monitoring.

Most operators use one of their four quarters to achieve their FCC requirements with a ground-based CLI. The ones that combine them prefer to have a snapshot of the actual interference that only a flyover can provide. But the ground-based CLI data can more effectively be used to find the actual leak source. A flyover is flown in a grid pattern at an average of 450 meters above the system and shows hot spots, but the data may be hard to use to pinpoint the source of the leak. There are pros and cons to both ways.

There are also pros and cons to combining the rifle and shotgun methods. A rifle program is dedicated and generally incorporated into a preventive maintenance program, whereas a shotgun program blankets an entire system more quickly and is more of a demand maintenance program.

It is a prudent and wise decision to incorporate the principles and benefits of both a demand and preventive maintenance program. The rifle is methodical. But the shotgun is valuable because it utilizes existing personnel that are out doing service calls anyway.

Both ways affect the bottom line. And the results should lead not only to FCC compliance, but also to better signal quality and more robust VoIP and Internet service, which are the ultimate targets.

Ken Eckenroth is VP technology for Cable Leakage Technologies. Reach him at ken@wavetracker.com.