“What Would Happen If I …”

RF design remains a mysterious craft. How can you get the most out of your propagation?

The following is taken from the introduction to the Radio World eBook “Propagation Analysis for Profit.”

At one time or another most people in radio management and engineering have wondered, “Just what could I do with this station if I were able to afford a power increase?” The phenomenon is particularly pronounced in the world of non-commercial radio but in fact is common throughout the industry.

Many professionals learned to ask the question while working in college FM radio, where stations operate at a bewildering array of various power levels. With pride perhaps exceeding the quality of the airwaves that could ever be achieved, those college kids couldn’t help but imagine the massive increases in listenership that would be possible if only their signals could reach more people.

After I graduated from college I had the opportunity to dip my toes into the world of the FCC allocation process with the assistance of a kind gentleman named Harold Dorschug.

Harold had offered free assistance to one of my client stations in making an application to the FCC for a power increase from 70 Watts to 100 Watts in order to achieve the protection of a minimum Class A facility. In those days the FCC was beginning to revoke the protections of the old Class D stations and most were being shepherded up to Class A status if it was possible to do so without causing interference.

Unfortunately, the FCC protection contours were more conservative in those days, so there simply wasn’t enough room at the time for all the Class Ds to increase in power. My client station had gone about as high as it could go.

Harold was a retired CBS engineer who had worked in master control the night of Orson Welles’ “War of the Worlds” and been a member of the first CBS television remote crew. He worked his final years at powerhouse WTIC(AM/FM) in Hartford, Conn. He was every bit the gentleman to me, a young and long-haired English major in jeans starting out as a contract engineer for all the non-commercial stations I could find in the area. I learned an enormous amount from him about how to read FCC graphs and calculate coverage and interference contours. It was my introduction to what I saw as real engineering. I was hooked.

In those days an application was completed with rulers and lines drawn on a map, with French curves to smooth out the intersections. Data on height above average terrain was gathered from contour maps along eight radials drawn in pencil on a geographic survey map. From the FCC rules and Harold, I learned the mathematics of protection ratios calculated in decibels and the logic of how to prevent interference.

Alas our efforts were doomed. The commission at that point in time wasn’t about to accept any waivers to allow an increase in power where it might cause any interference; they already had enough complaints to deal with. And the idea of paying for a directional array to achieve higher power while protecting a nearby station was beyond the budget of my client.

We took our rejection and moved on.

THE COMPUTING REVOLUTION

Today we still ask: How would my coverage be affected if I moved my FM antenna? Changed height? Increased transmitter power? Added a fill-in translator?

Now the work I learned to do by hand is done better and more accurately by software. The first-generation programs would calculate contour interferences based on the FCC curves and spit them out as charts. The latest programs can generate presentation-quality coverage maps that are as useful in the GM’s or sales manager’s office as in the FCC’s inbox.

Not only can we look at geographic coverage, we can with the click of a keyboard pull up highly accurate population surveys to evaluate the benefits of increasing coverage. And advanced models allow detailed views of where exactly we can expect to offer a usable signal and where it is likely to fail, based on our operating parameters and location.

A barrier to understanding the mysteries of RF engineering over the years has been the cost of the software that provides the necessary calculations. This is why it is fun for example to highlight the coverage tool that Nautel, a sponsor of our eBook, recently developed that shows a Longley-Rice map of the coverage area for any radio station. This mapping tool is free to use and is a part of an RF Toolkit that Nautel makes available on its website; registered users can use this tool to view the coverage of any station they wish.

Since those early years when I peeked behind the veil of the FCC allocation process, I have been fortunate enough to get access to modern software tools and given the opportunity to learn how to use them. I have become fairly well acquainted with the FCC’s allocation process and the engineering support required to get a successful result on more than one application. I have also had a chance to explore the subtleties of antenna designs and directional arrays, both AM and FM. While many have helped me to learn about the science of engineering radio stations, I tip my hat in particular to Doug Vernier, whom I interviewed for this eBook and who has been a great mentor and teacher.

This story is excerpted from the Radio World eBook “Propagation Analysis for Profit,” one of the growing Radio World library of free eBooks.

THE MYSTERIES OF PROPAGATION

The premise of this ebook is that new software tools and data sets have changed the game when it comes to answering questions about managing propagation for profit, whether it’s for an FM, an AM or a shortwave facility. As a mature medium, broadcasting is now seeing a lot fewer new stations at high power, at least in the United States; but there are plenty of improvements to propose and, if substantial enough, to build to an operating condition. If you are one of those people who have wondered how it all works, read on. Enjoy!

Access the free eBook at radioworld.com/ebooks.

Michael LeClair, CPBE, is a longtime contributor to Radio World and is former technical editor of Radio World Engineering Extra.



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