Electronic Broad Banding of VLF/LF Antennas for FSK Radio Communication

Narrow-band VLF/LF antennas are broad banded by synchronously tuning the antenna to resonance at the instantaneous frequency of the FSK signal to be radiated. The broadbanding technique employed is the switched magnetically coupled reactor. By appropriately timed switching of reactors the effective inductance of the antenna tuner is maintained at or near the value for continuous radiation system resonance. For a given antenna, radiated power, and frequency shift, the number, size, and coupling of switched reactors are computed. Network poles are determined and system transient response of antenna and reactor current are determined for both up and down frequency shift. An example based on the U. S. Navy VLF antenna at Balboa, Panama, is worked out.