09/05/2019
Wow, those are coils!
WWVB, used throughout the United States to synchronize local clocks and oscillators, sits on the same property as WWV. The broadcasts are 50kW at a low frequency of 60 kHz, which has a wavelength of 5000m (3.1 miles). A desired quarter wave vertical antenna would have to be 1250m, ¾ of a mile, or 4100 ft tall. To get it shorter (125m), additional length was added above the vertical radiating element horizontally in a lattice called a capacitance hat or top hat, stretched between 4 towers, each 400ft tall (image). The vertical element terminates in a structure know as a Helix House, which is about 2 stories tall.
To reduce and hopefully cancel the capacitance introduced by the top hat and shorter antenna, the Helix House houses a large inductor and a variometer (variable inductor) so the system can be tuned. (image) The image shows the copper inductor coil (about 3 feet tall), and the darker inductor positioned horizontally is the variometer. A computer controls the variometer and will make adjustments for such things as ice and windy conditions automatically. The computer looks for a phase difference in the voltage and current at the transmitter, and if needed, a 3-phase motor rotates the rotor in the variometer to adjust and match the system. The feedline to the antenna starts at the far end of the variometer, heading upward to the top of the Helix House.
Be sure to tune in for the 100th anniversary of WWV and special event station WW0WWV, on the air from September 28 through October 2, 2019. Please see WWV100.com for more details and our operating frequencies during the event.