Tour of WRMI
Let us take you on a virtual tour through the WRMI shortwave station in Okeechobee. We would like to show you this unique facility that we have been entrusted with.
As you drive up the road to WRMI, you will no doubt notice the many towers, lines, telephone poles, satellite dishes and other equipment all around you. The 23 antennas consist of a total of 68 towers. All of this is part of the transmitter site you know as WRMI.
You begin your tour when you come through the front door and into the reception area. The offices are those of the management at WRMI. The office of general manager Jeff White is located behind the receptionist's desk. The office of Facility Manager Terry Elders and Machine Shop Manager Pat Travers is located down the hall.
Conference Room and Library
The center office contains a library of technical books, manuals and records, as well as some audio recordings. It is also used as a conference room; thus the table and chairs. A giant map of the world is located on one wall showing locations of listener reports received from around the globe.
The next stop on your tour is the control room. Here you will get a feel for what really happens at WRMI. This is where we control the audio, the transmitter frequencies and the antennas. This is the heart of the operation here at WRMI. Twenty-four hours per day, 7 days per week, at least one operator is on duty in the control room.
The control room operator is responsible for making sure the correct audio feed is played on the proper transmitter. It would be disastrous if the listeners were expecting a program in English and they heard a Russian program. So the operator's job is very important. Different computers play different programs simultaneously. They are labeled as System A, System B, System C, etc. There are also satellite receivers to receive programs from certain clients via satellite. The audio from each system can be fed to any of the 13 transmitters through an audio switcher called a Dynair.
The rest of the control room is geared to the transmitters. Since we may operate a transmitter on different frequencies and up to three different antennas during a day in order to reach the locations desired, these things are controlled in the individual racks.
The transmitter racks are the short racks along the sides of the control room. They have several pieces of equipment designated for a specific transmitter. The top panel has an audio attenuator that allows us to control the audio level on each transmitter. This audio level can be seen on the Belar monitor below the attenuator. The moving meter indicates the audio on the transmitter and the percentage of modulation. The other meter is set each time a transmitter goes on and indicates the RF carrier level. This monitor is attached to a pickup at the wall where the transmission lines exit the building for the corresponding transmitter.
Below that is the PTS synthesizer which is used to change the frequency on a transmitter. Because shortwave is affected by the sun, our frequencies have to change during the day to make sure we are reaching the area of the world desired. We operate on various frequency bands between 3 and 30 Megahertz.
Next is the antenna switch controller which allows you to select the antenna you want to use with each transmitter. The LED's on the panel will light up to let you know which antenna is connected. This device controls large switches up on platforms around the building.
The bottom half of the rack has an Optimod audio processor which can tailor the high or low audio frequencies and the compression of the audio signal to each transmitter. This piece of equipment makes the necessary audio adjustments.
Each rack also has a patch system which can be used to bypass the audio processor if necessary.
Transmitter Monitoring Racks
At the other end of the control room from the console are some racks containing transmitter monitoring equipment. The frequency counter is used to verify that the transmitter is on the correct frequency.
Studio and Computer Room
This room is soundproofed and completely shielded from RF energy that could interfere with operations. Although most of our programming comes from outside sources and is recorded in studios around the world, we do some recording and audio production in Okeechobee in this studio. It is also capable of doing live broadcasting if needed.
The studio shares space in this room with several computers that do everything from writing programs that read the transmitter frequency to writing manuals that document equipment or systems. They also have databases which track inventory or documentation, and they can produce schematics and mechanical drawings of various pieces of equipment on site.
In the transmitter hall you can see the fronts of all the transmitters along the walls. They are the metal surface areas which are framed into the walls with doors between each transmitter. From here we can turn the high voltage on and off and do any tuning needed to operate the transmitter.
As you will notice, most of the transmitters look about the same. That is because Family Radio engineers built the eight transmitters numbered 7-14 themselves.
There are two Continental transmitters (transmitters #3 and #4) which look similar to the ones which our engineers built. They were purchased about two years before WYFR moved from Scituate, Massachusetts to Okeechobee. One was originally installed in Scituate and the other was stored in Dallas until it was sent to Okeechobee. Many modification were made to improve them and make them more like the ones that our engineers built.
Both the Continental and the Family Radio FSI 100 will automatically change to the next scheduled frequency if they are preselected and armed ahead of time. This makes changing frequencies much more efficient, especially when we have to make frequency changes on several transmitters at about the same time.
The transmitters you see with all the cranks on the front are older style Gates transmitters and are the original transmitters which made up WYFR along with transmitter 6. Every time we change frequencies on these transmitters we have to manually adjust the cranks to predetermined locations. The presets are recorded on cards on the front of the transmitter.
We have twelve 100,000-watt and one 50-thousand watt transmitters. They are all high-level plate modulated. Some of the transmitters are air-cooled which others use water- or vapor-phase cooling.
Behind the Transmitters (#2 and #3)
As you can see behind the transmitter hall wall, there are cabinets and a cage filled with large components extending back to the building wall. All of this equipment makes up a transmitter.
Each transmitter has cabinets with audio amplifiers, RF amplifiers and control circuitry. They also have large power supplies in the cages that create over 10,000 volts to power the transmitters. With all this voltage, this equipment can be very dangerous. During the station's history, fortunately no one has been seriously hurt while working on these transmitters. Safety has to be a primary concern because you might not get a second chance.
You will also notice that the transmitters have large blowers or heat exchangers in the power cages. That is because the transmitters generate a tremendous amount of heat that needs to be dealt with. Even with all this equipment it can be over 100 degrees Fahrenheit behind the transmitters in the summertime, and the building's attic often is over 120 degrees.
The test room is adjacent to the studio. It is shielded in order to keep the RF from the transmitters to a minimum while using certain test equipment. The studio and the control room are also shielded to keep the RF down -- very important of course when you are recording a program or broadcasting live. As you can imagine, having 13 transmitters broadcasting over a million watts of power could be a problem for some equipment.
The test room is used to test components, audio equipment and the maintain our test equipment. It is not unusual to see a piece of equipment dismantled in pieces and attached to several test instruments on the bench.
Daybook and Equipment Storage
The daybook area is used to store most of our test equipment on the shelves. This keeps it together in one central location, although it may be used anywhere in the building.
We store copies of the equipment manuals in the files here, and each staff member has a file cabinet drawer to store information particular to his job and current assignments.
We call this the daybook area because we keep a notebook on the table here in which anything that breaks, or any out-of-the-ordinary observations are recorded on a daily basis. First thing each morning, at least one of the engineers has to look at what has been written up and make repairs as soon as possible. These are the ongoing repairs which have to be done to keep WRMI on the air.
Transmitter Hall (Transmitters 11-14)
In this part of the transmitter hall you will notice that we have a lot of work benches and one of two shop areas. With our transmitters there is frequently some repair work which has to be done. Just the everyday changing of frequencies can wear out many of the variable inductors or other transmitter components. That means that it is not unusual to see someone working on parts from a transmitter in this area. We must also fix anything that breaks down due to an arc. At times it is like creating a new piece to replace the charred remains of a component.
In the control room you saw a control head that was used to determine which antenna a transmitter was on. That head controls the antenna switches outside, but you can see one close up in this area. We build, test and repair these switches here. You can imagine what can happen to a switch when 100,000 watts of RF power decides to do a little burning on one of these switches. The switches are controlled via underground cables that go from the control room to the switch platform outside. Switches which are ready to be used are stored in the daybook area.
Loading Dock and Pole Barn
What happens inside the building is only part of the activity here at WRMI. We not only have transmitters and audio equipment, but we also have an extensive antenna field. This is maintained by members of the staff which form the field crew.
As you look around the field, you will see around 600 telephone poles, miles of wire and 68 towers from 120 to 180 feet in height which hold up the antennas. You can also see the switch platforms we told you about earlier. Remember that someone builds and maintains all of this, and that is our field crew.
They use the equipment you can see stored out here, both in the main building and in the pole barn. They use the large orange line truck and other vehicles to construct, repair, take down and modify the antennas and the feedlines that connect the transmitters to the antennas.
The 23 antennas we use here at WRMI are not all of the towers you see across the field. The towers actually hold the antennas up, and the wires you see hanging between the towers and tall telephone poles are the actual antennas. We have several types of antennas which you will see surrounding the building.
We use 10 double rhomboid antennas in four sites. They are each supported by right towers. If you could look down on them from above, they would look like two diamond-shaped sets of lines on top of each other. These are long-distance antennas that shoot the signal at the horizon to get it as far around the world as possible.
The double rhomboid antennas are on 44 degrees (Europe), 87 degrees (Africa), 142 degrees (Brazil) and 160 degrees (South America). They have antenna gains which run from 20 to 30 dbi depending on the transmitter frequency. The take-off angle of the antenna varies from 4 to 18 degrees. The half-voltage azimuthal beamwidth of the double rhomboid varies from 11 degrees to 16 degrees depending on the antenna.
Log Periodic Antennas
Our second type of antenna is the log periodic, and we have 12 of them. You drove between two of them when you came in the driveway. They are sloped at about 45 degrees and are hung between two towers and three tall telephone poles. The wire you see zig-zagging back and forth is the antenna. This antenna shoots the signal up in the air for short hops like to Mexico or Cuba. We use three types of log periodic antennas on azimuths of 140, 151, 160, 181, 222, 285, 315 and 355 degrees. They are used to broadcast to the Caribbean, Central America, Mexico and Canada. The log periodic’s antenna gain ranges from 12 dbi to 18 dbi depending on the antenna type. They have a take-off angle which ranges from 12 to 45 degrees. The half-power azimuthal beamwidth of the log periodic is 38, 68 or 90 degrees, depending on the type.
The third type of antenna we use is a curtain. This is the first antenna you see when coming in from Highway 441, and it hangs vertically between four towers. It is a long-range antenna with a wider signal coverage area. You may want to take a closer look at it when you leave.
A dipole curtain, which has a 2-wide, 4-high curtain with a passive reflecting screen, is located in the northeast corner of the property. It is on an azimuth of 44 degrees (Europe), with a gain of approximately 19 dbi. The take-off angle is about 8 degrees, and the half-power azimuthal beamwidth is 40 degrees.
The antennas are connected to the transmitters by the feedlines you see all over the property. A feedline is made up of four wires, with pairs of wire side-connected by aluminum clips to form a two-conductor line with a 300-ohm characteristic impedance. It is capable of handling 100,000 watts of RF power.
South Shop Area
The south shop area is used in the manufacture and repair of transmitter and antenna field components. Much of the antenna switch construction happens here. This is where most of the woodwork occurs because the table saw and sanders are located here.
There is a display of equipment and parts here. This includes old tubes and capacitors which you can see close up. Also, it includes some parts which were burnt up in the transmitters to illustrate the destructive potential of the equipment we are working with.
This is the area where we store our large tubes and vacuum capacitors. Working with high voltage components, we need a way to be able to test them before we install them in a transmitter. We do this in the Hipot Cage.
We have two Hipots. One is AC voltage and the other is DC voltage. They can develop over 50,000 volts so we can check tubes and high-voltage capacitors. This allows us to determine if we have an air leak, gas or an arc inside a capacitor or vacuum tube. With the Hipot we can take a gassy tube which would be unusable otherwise and de-gas it by slowly raising the voltage and burning out the gas. This saves us money by not having to buy a new tube or having the old one rebuilt.
Shop and Garage Area
The shop and garage area is used primarily by our fabrication crew. Here the fabricators create parts or repair components which have been severely damaged. They are extensively involved in major physical modifications to equipment or building projects. The fabricators have to be proficient in welding, using equipment such as lathes, milling machines and all kinds of hand tools. They need a tremendous amount of creativity and skill to make the things that the engineering staff dreams up.