As the LBA Antenna Turns

As the most experienced firm offering AM detuning services, LBA gets some complicated requests. LBA’s professionals are mostly unsung when they accomplish these missions.

Kathryn Tesh and the LBA team recently set straight a cellular tower detuning project in the Pacific Northwest, saving the cellular customer considerable money in the process. So it was a bit of a Holiday gift to receive kudos from both the station consulting engineer and the wireless carrier project manager. Here’s what they said (slightly edited for privacy):

From the consulting engineer:

“The ownership of K*** has asked me to respond to the engineering study performed to determine re-radiation potential.

I see no problems and I appreciate this careful work.  We have a history of concern expressed by the (on channel) station in Seattle and consequently have been careful to maintain our night-time directional.

LBA has done excellent, careful engineering.  Please proceed.”

From the client carrier manager:

“Thanks I have the reports and believe this closes out the projects.  I hope you have already invoiced for everything and I have approved what has come my way.

I agree with the K*** engineer.  These projects were somewhat complicated with the three sites and our early construction of one of the towers.  I am very pleased with how LBA handled the whole thing. My compliments to yourself, Mike and the LBA team.”

And, as we write this, here’s a thank you just in on another project!

A carrier construction contractor needed really fast response involving the dispatch of an LBA engineer to a remote California location over Christmas week. Unfortunately, an LBA competitor had walked away from the project, leaving the contractor stranded with a deadline. The LBA report was on the client’s desk this morning!

Here’s what the Program Director said to Kathryn:

“Excellent work.

I have reviewed the report and I appreciate the completed analysis.

I may have questions later today but for now this report as delivered is much appreciated.”

We very much appreciate the customer feedback. LBA has been performing consulting services since 1963, always with customer satisfaction as the #1 priority. Please contact Mike Britner to enjoy LBA superior professional services in AM and EME wireless compliance services.

Lawrence Behr Associates cleared the path for a new electricity transmission line in New York that that could not be energized until interference problems with a Rensselaer, N.Y., AM radio station were resolved to the satisfaction of the New York Public Utility Commission.

After extensive onsite and computer analyses, LBA engineers determined that 8 of 33 tall power towers on this line in the proximate area of station WGDJ-AM would disrupt the stations licensed coverage pattern and require installation of detuning systems.

Utility constructors installing AM detuning system on East Greenbush 345 KV transmission tower.

The transmission towers carry a 345 kV electrical power line from a 635-megawatt natural gas fired power plant constructed in Rensselaer by Empire Generation Co. LLC. The distribution system has 70 towers in all, the last of which were erected last summer. The question was how many of them near East Greenbush, N.Y., would cause signal interference with broadcasts of the AM station. The interference would have created a violation of FCC rules governing the integrity of broadcast signals.

Transmission towers often are a height that makes for efficient radiation of medium wave AM signals. The broadcast AM signal is intercepted from the environment by the power tower and “reradiated”. This reradiated AM signal interferes with the designed coverage and interference of the AM broadcast antenna system. The Federal Communications Commission licenses AM station antenna systems to very tight tolerances, and only a few percent reradiated powerline signal can seriously impact the licensed pattern performance.

The proper evaluation and remediation of power line reradiation can be complex. The multiple transmission towers and the coupling between them through lightning shield wires can be a challenging analysis, but also spread the impact much more broadly than would a single tower. These interconnections form conductive loops which have vastly different electrical properties than single towers. Normally, a technique called “detuning” is applied, along with modifications of lightning shield wires. The recent practice of embedding fiber optic cable in these wires has made these mechanical modifications quite a bit more complicated.

To evaluate and resolve the New York problem, Lawrence Behr Associates was called in by CH2M Hill, an international consulting engineering firm based in Colorado. The eight disruptive transmission structures were subsequently identified through field measurements and software modeling. Their negative impacts were remediated by an AM protection detuning process, allowing the project to proceed. The offending structures were detuned using custom-engineered LBA Technology hardware along with modifications to the new power line. Modifications were carefully designed for safety and usability in conjunction with CH2M Hill and the owners, and implemented by LG Constructors. Necessarily, all detuning hardware was constructed, installed, and documented to rigorous utility standards.

LBA engineer Mike Hayden adjusting AM detuning system control box.

LBA has employed a similar process hundreds of times to detune cellular industry towers with AM radio interference problems of their own. While technological applications vary in each case, they are rooted in the same family of engineered solutions. This was an important design consideration, as renting transmission tower space to wireless carriers is an important revenue source for utilities. In the event the detuned towers were to be rented to a carrier to support their antennas, the AM dutuning documentation would also support the carrier’s FCC AM protection requirements.

Interactions between high voltage transmission systems and AM stations are expected to grow in future years. Thousands of miles of powerlines are planned to support the smart grid, wind turbine, and photovoltaic power generation. Many of these will pass near AM broadcast antennas. It is vitally important for utility planners to have proposed routes reviewed by an RF engineer, like Lawrence Behr Associates, early in that process. If lines can’t be rerouted, then detuning can be incorporated in the design process, at great savings over construction stage delays or modifications.

For more information, contact Mike Britner.