This is one of a series of articles about AM radio, its challenges and successes.
When it comes to AM radio stations in the United States, perhaps no engineer has quite the number of sites to worry about as does John Warner.
Warner is vice president of engineering for AM for Clear Channel Radio and has responsibility for maintaining and im¬proving literally hundreds of AM stations.
Photos from the Boston-area triplex project. This is the WKOX phasor. ‘The building footprint couldn’t be enlarged,’ Warner said, ‘so I specified canteliver trusses to create a cathedral ceiling so we could make the phasor two stories high.’ With that many stations, there are always interesting projects in various stages of completion. RWEE spoke recently with Warner to hear about his latest and to learn from him how he ended up working in AM.
When did you first develop an interest in radio?
I had an early interest when I was about 8 or 9 years old. I owned a crystal set when I was young. My father was interested in radios, and I built a small radio as a scouting project. My mother actually taught me to solder. During World War II, she worked at Bendix Radio in Baltimore, which manufactured aircraft and tank radios for the war.
We lived on a farm when I grew up, and I became interested in antennas so that I could pick up different kinds of radio signals. I used to listen to all the European broadcasters via shortwave, and I experimented with long-wire and curtain array antennas. My father encouraged my interest in radio, and for one of my birthdays he gave me a telephone pole, which he then helped me to put in the ground to use as a tower that I could use to make experiments.
Did you attend any formal engineering school?
I attended the University of Maryland for two years in 1966 and 1967 and studied defense electronics and electrical engineering. I did not get a formal degree because my family did not have enough money to let me complete college, but I later went back to school and took further engineering courses at Johns Hopkins.
Where did you first begin working in radio?
My first job in radio was at station WBAL in Baltimore in 1979. I had a First Class radio license, and that allowed me to be a transmitter engineer for them. WBAL is a 50 kW clear-channel AM on 1090 kHz that began broadcasting in 1925. As a high-power directional array, WBAL was required to have an FCC licensed operator on duty at all times.
Equipment layout. ‘There was just enough room in the building to install the equipment with minimum safety clearances.’ At WBAL I met Harrison Brooks, who had just retired before I started working there. He was the engineer who helped build the current transmission plant in 1940, which uses a directional array at night. Harrison was actually an electrician on that project, but he became so enthused about radio from working there that he became the chief engineer of WBAL after it was built.
Harrison taught me a lot of the history of WBAL and about broadcasting in general in the Baltimore area. He lived nearby and used to drop by to visit the station and keep an eye on any changes or new technology that we installed.
Do you have other mentors who have helped you in your career?
I also learned a lot from Ron Rackley, whom I met in 1986. We were installing a new Continental 317C at WBAL, and to improve the stability of the array, we also replaced the sample system at the same time and did a full proof. Ron and I struck up an immediate friendship while working on that project and we’ve stayed in touch ever since.
Ron gave me my first copy of the MiniNEC code, which is used to model the behavior of antennas. In those days it ran on an 8086 class computer, and it would take hours to do a tower model. I remember that you could start a model in the morning and let the computer run all day while working, and come back to find that it had just finished around 5 p.m. With the enormous improvement in computer power, modeling for AM has become so much simpler and much more important.
What kind of work do you do as VP of engineering for AM for Clear Channel Radio?
I joined Clear Channel about 10 years ago when Jacor was acquired by them in 1999. I am responsible for overseeing the design and construction of new AM facilities and the maintenance and refurbishing of existing AM stations. At any given moment there are approximately 250 to 300 AM stations that are in the Clear Channel portfolio.
For some of the projects I do the design work myself, and I always have some design work with me. I often do this kind of work while on airplanes, traveling around the country to different sites. I actually still use a slide rule for some of my designs rather than using a keyboard. It’s easier sometimes to calculate on the slide rule when looking at combiner systems. There is a tradeoff between isolation and bandwidth, and you need to iterate component calculations to adjust between these two. The slide rule makes you think rather than just using a computer program to plug in numbers until it works.
Pre-cast tuning houses were 14 by 20 feet and each weighed 60,000 pounds. To keep them up out of the flood plain they were set on caissons that were 3 feet diameter below grade and 1-1/2 feet diameter above grade. Temporary roadways were built to support the crane and trucks carrying the buildings; the roadways had to be removed after construction to restore the wetlands. With so many stations to maintain, I generally have between 15 to 20 projects going on all the time, involving site refurbishment, combining stations into a common antenna system to improve coverage and station moves.
You recently completed an interesting project in the Boston area that brought three stations together into one site.
The project was begun by Fairbanks Communications, which owned station WKOX. Originally in Framingham, WKOX operated at 10 kW daytime and used a two-tower directional array at night at a reduced power of 1 kW. WKOX was bought by AM/FM, which then later merged with Clear Channel.
By moving 10 miles closer to the city of Boston, WKOX was able to upgrade to a full 50 kW signal for both day and night and put a full-time signal over the entire metropolitan Boston area. The site they moved to was a new five-tower array at the old WUNR transmitter site in Newton, owned by Herbert Hoffman.
WUNR originally operated at 5 kW unlimited using a two-tower array. WUNR upgraded to 20 kW night and day as part of the project. Station WRCA, which is owned by Beasley, was also part of the move and was able to achieve an upgrade from 5 kW directional day and night to 25 kW day and 17 kW night time power by using the new five-tower antenna array.
You can see that this was a complicated project but the substantial increases in power made it attractive to all the owners.
I began working on this project in 1999. It took about eight years to get the necessary approvals to start construction. The local zoning and environmental approvals were particularly hard to obtain due to opposition from the local community.
What kinds of unique challenges were involved?
To start with, the extended time required to get local approval means extra work with the FCC. Before you can commence the zoning and approval process, you must first obtain the construction permits for the proposed facilities. But because of the delay in local approvals, we could not complete this project within the typical window of three years, so we were forced to file numerous extensions with the FCC explaining that the delays were out of our control. Every six months, we had to file a report on the progress of the project in order to keep the construction permits alive.
The three phasors are placed in the building and assembled. Once construction began, it took a little over two years to complete. We built this site around an operating radio station that needed to stay on the air while we took down two towers that were 353 feet tall and replaced them with five towers. The new towers were less than 200 feet tall, which was an advantage because they no longer would require FAA marking and lighting.
The tower site is a wetland area that is adjacent to the Charles River, and the water table runs about 3 feet below grade. In order to put conduit below the frost line we had to go below the water line, so we ended up using PVC conduits where all the joints had to be sealed.
Due to the wetland site, we used helical screws at the anchor points rather than conventional concrete anchors. The tower bases were of conventional concrete pier construction.
But the most difficult part was the environmental restrictions placed on the project. We had to interrupt construction several times during the breeding cycle of the blue spotted salamander, which is classified as an endangered species. There could be no open trenches on the site between Feb. 15 and May 15, and trenches could not be left open at night over the weekend. We had to leave a clearance of 4 inches at the bottom of our tower safety fences to permit animal movements.
All told, there were over 60 different conditions we had to meet to satisfy the local zoning, including the requirement that the stations hire an environmental consultant to work for the city and monitor the project for compliance.
During the project there were no stop work orders and no violations of the zoning requirements. At the end of the project we had to appear before the local con¬servation commission, and they actually commended us on doing careful construction.
I want to point out one other unique aspect to this project from an engineering standpoint: These were the first three stations to use Method of Moments modeling to license a directional array.
Were stations in the triplex going HD?
No. In a triplex with nine filters and their component stray reactances it can become very difficult to get all of this to work with HD so we decided not to pursue that at this time.
The original WUNR transmitter building had a flat roof. Clear Channel had to make the building look like surrounding houses. The windows are fakes. Do you have any other interesting projects in the pipeline right now?
We are just finishing up an eight-tower directional array in the St. Louis area. This one will also be licensed using Method of Moments.
Are there differences in a project when using Method of Moments?
What I am finding is that when using Method of Moments there are some tricks and techniques that you learn. It is necessary to build the towers first and then build the model after construction. The model needs to be calibrated due to the velocity of propagation of the tower system not being equal to 100 percent.
With an eight-tower array there is a lot of measurement work involved in calibrating the model too. You have to measure the base resistance and reactance of all the towers with each one grounded and the others floated and make up a matrix of all these measurements.
We used the Rackley network analyzer and directional coupler method to make the measurements faster. To keep from having to haul a network analyzer all over the tower site and provide power at each tower base, we used the sample lines to measure the tower impedances one at a time. By calibrating the network analyzer to compensate for the sample line we were able to do all the measurements from inside the transmitter building.
The model has to be compensated for differences in tower heights and tower variations, such as if the site terrain is not completely level. Note that towers toward the interior of the array will have different impedances from towers on the outside due to the mutual coupling between the towers.
Once you calibrate the model to actual conditions, you can figure out the operating parameters for the array. These calculations have to be iterated back and forth until it all converges into the correct values for the system components.
It has been an interesting and valuable experience.
On FM translators for AMs: Do you find this a helpful development?
We do have a few translators repeating AMs. I haven’t been involved. The last time there was a translator filing window we licensed a bunch; at that time, AM on FM wasn’t allowed. Since that is now the case, I can see translators becoming more valuable but I’m not aware of a company-wide effort in that direction. I would think a translator would be beneficial to an AM having a high NIF (nighttime interference-free contour) limit.