Ground Wave Emergency Network

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The Ground Wave Emergency Network (GWEN) is an array of radio transceivers distributed across the continental USA, operating in the VLF frequency band, and intended for military communications during a nuclear war.

GWEN was part of the Strategic Modernization Program designed to upgrade the nation's strategic communication system, thereby strengthening deterrence. The GWEN communication system, established in the late 1980's, is designed to transmit critical warning and response messages that would be immune to the effects of a high-altitude electromagnetic pulse, or HEMP. HEMP typically would be generated by a high-altitude nuclear burst. By precluding the use of HEMP to cripple communications, the GWEN system would strengthen deterrence and enhance the ability of the U.S. to prevent war.

In the GWEN system, originating stations send ultrahigh-frequency (UHF) signals by broadcast towers for line-of-site receipt at RNs. The RNs form an unmanned network throughout the US, with individual RNs at spacings of approximately 150 to 200 miles. The RNs transmit received messages via low-frequency (LF) signals for ultimate receipt by Receive-Only terminals at existing military communication buildings. By utilizing LF ground transmission the GWEN system minimizes the potential effect of HEMP on military communications.

A typical RN station is located on an unmanned site of approximately 11 acres. Such a site features a longwave transmitting tower (generally between 290 and 299 feet tall), a backup diesel generator with a two chambered fuel tank having a capacity of 1,020 gallons, an antenna tuning unit, and a radio processor. This equipment is housed in three shelters. Two of the shelters are located in a fenced area at the perimeter of the property, and the other at the base of the tower. The equipment area and the tower base are surrounded by locked, eight-foot high-chain link fences topped with barbed wire. In addition, each RN has a UHF antenna and an LF receive antenna on a IO-foot mast located in the equipment area. The main GWEN antenna operates intermittently in the LF band at 150 to 175 kilohertz (kHz) (e.g., the bottom of the AM band is 530 KHz). The peak broadcasting power is from 2,000 to 3,000 watts. The UHF antenna operates at 20 watts, between 225 and 400 megahertz (MHz).

Since the fiscal year 1998-1999, the GWEN system has been replaced by Milstar satellite terminals and GWEN Operations and Maintenance funding has been terminated.

Source: Closure of the Ground Wave Emergency Network (GWEN) Relay Nodes, USAF EAIP 1998.