A trip to the Caribbean island of Bonaire gave me a chance to visit PJB3, a Trans World Radio AM station transmitting Christian-based radio on 800 kHz.
I read about the Bonaire facility in a Radio World article seven years ago. The site is said to have the largest AM transmitter in the Western Hemisphere. Seeing this high-power station was worth the effort.
Bonaire is a Dutch-held desert island about 50 miles north of Venezuela and about 850 miles north of the equator. It is one of the “A B Cs,” along with Aruba and Curacao, formerly the Netherlands Antilles. Bonaire is 24 miles long and three to seven miles wide with a population of about 24,000.
TWR has been broadcasting to the world since 1952. Its Bonaire operation started in 1964 with a 500 kW tube-type transmitter (Fig. 1), which was very expensive to run. It was later downgraded to 100 kW to save money.
In 2018 the station turned on a Nautel NX-400 solid-state transmitter, which produces 440,000 watts of RF, seen in Fig. 2 with engineer Matt Folkert, N3FLW. That upgrade increased the population within its reach from 50 million to 100 million people.
With Modulation Dependent Carrier Level technology they were able to reduce the power cost. Total power includes necessary air conditioning to keep salt air out and the temperature down from the year-round day and night average of 85 degrees.
The three antenna patterns are shown in Fig. 3. The four 478-foot towers are 140 degrees in electrical height at 800 kHz. That puts them in the 700-ohm range of self-impedance. As you know, impedance changes under directional antenna conditions. Kintronic Labs in Bluff City, Tenn., engineered the four-tower directional antenna system.
Jim Moser, senior staff engineer at Kintronic Labs, told us that for the North and South pattern, the front two towers with respect to beam direction are driven and the rear towers are reactively terminated to act as reflectors.
When the operation is switched, the pair of towers that were operating as reflectors are now in the front and driven, and the previously driven towers are reactively terminated.
The patterns are similar, each with theoretical gains of over 13 dBi, but with each using its own power dividing networks for independent control.
The third pattern, covering portions of the Caribbean, consists of one driven tower with the other three towers reactively terminated to provide some beam shaping with approximately a 9.5 dBi maximum gain.
Isolation coils at the base of each tower provide access across the base insulators for the sampling system and tower lighting as well as providing a static drain path. The isolation coils are tapped in order to be incorporated as part of the matching and terminating networks and provide additional control of the high tower drive impedances.
Moser went on to say that he was not aware of any domestic systems using parasitic towers to shape the pattern, but there are multiple systems internationally that use the technique. It is more common in high-power systems operating with 100 kW and above.
The closest related practice domestically is using reactive terminations to detune towers in an array such that the tower has a near zero field contribution to the desired pattern.
Nightly schedule
Back in the day, with the half-megawatt tube transmitter and production staff on site, it took as many as 100 people to run PJB3. Today only one engineer is needed, and just a few production staff. Recorded audio from reporters in countries being served is sent via FTP to Bonaire. In Fig. 4, Station Manager Jason Helmholdt is at the controls of an Axia IQ console, where programming is mixed for airing.
The work is supported by paid local staff as well as world-wide missionaries who donate their time to support the mission of TWR. Some engineers pay their own way to help.
The power company knows PJB3’s broadcast hours and is prepared for the load. The utility gets a call from the station if the transmitter is scheduled to be run at other hours.
The facility is supported by a bank of five diesel generators that can make 14 megawatts total. Solar and wind turbines with batteries are a part of the equation for consistent power day and night. Not all islands are so blessed.
TWR Bonaire is silent during the day but comes alive at night. From 7:30 to 8 p.m., they broadcast in English to the Caribbean islands, then the pattern is switched to the northwest from 8 p.m. to midnight, when Spanish programs are sent to Cuba away via skywave bouncing off the ionosphere. Yes, they put a reliable signal into Cuba some 900 miles away.
The antenna is on the southeast pattern from 4:30 to 6 a.m. when Portuguese is beamed as far as 1,200 miles into Latin America, again by ionospheric reflection. Then from 6 to 7:30 a.m. the station is nondirectional with Spanish programs to the Caribbean Colombia and Venezuela. Listeners know when to tune in.
In case of bad weather or emergency, the Netherlands government advises citizens from Saba to Aruba to tune to 800 kHz. This powerhouse station is there to provide accurate information.
Speaking of weather, the island is surrounded by the salty Caribbean Sea. That means tower painting is required frequently.
In the case of the TWR towers, each tower gets serious maintenance, with rusty parts replaced, then scraping and painting every four years. That job requires 2,500 labor hours because it takes three climbers on a tower and three people on the ground. This happens when the station is off the air during the day. How convenient!
Climber Lionel Cicilia wasn’t on a tower the day I visited, but he showed his climbing gear (Fig. 5). He’s shown with a paint scraper in his left hand and a paint brush in the right.
There is also an electronics shop for repairing equipment on site. In Fig. 6 Matt Folkert tackles a Belar AMM-2A Modulation Monitor that needs attention. Shipping equipment for repair is no easy task when items need to go through customs. Repairs are better done on site.
Matt Folkert’s history in broadcast began in 1980 with HCJB radio’s shortwave ministry in Quito, Ecuador. Matt was hired by the Voice of America and participated in its modernization effort until 1983; he then was with Radio Free Europe/Radio Liberty as a project engineer until 1996. Matt later worked as a technical consultant in the U.S. radio industry until 2019. After retirement, he volunteered with Reach Beyond, Far East Broadcasting Company and TWR at locations around the world.
TWR is an evangelical ministry using radio to reach people worldwide. You can learn more about the organization at TWR’s website and the Bonaire operation at has its own website as well.
