The U.S. Army is interested in innovative dual-use technologies to develop compact low frequency transmitters in the VLF (3-30kHz) spectrum with an antenna size significantly smaller than the wavelength of the carrier wave for underground two-way communications. Enig Associates, Inc. (âENIGâ) is proposing to address the Army's Cross-functional Team Priority #4 Network requirement with a low-SWaP transmitter system which has a volume of 50cm x 20cm x 20cm and a weight of 20 lbs (i.e., size and weight of a briefcase), and consumes 50W maximum to transmit a 10 fT magnetic VLF signal in a free space up to 1km distance, undersea down to 50m, and underground down to 300m. Radio frequencies at the very low-end of the electromagnetic spectrum are attractive for a number of defense and civilian applications for long-range two-way communications in underground and undersea. ENIG is proposing to demonstrate a very compact, man-portable, two-way VLF communication system using electron vacuum tube transmitt
