Echo One was the first subspace amplifier deployed by the United Earth starship Enterprise. It was deployed in July of 2151.
In September of 2151, Echo One was destroyed, along with Echo Two, by an unknown alien vessel. (ENT: "Silent Enemy")
Echo One was used by Vice Admiral Forrest to relay a Vulcan request for assistance at Paan Mokar to Enterprise in 2152, suggesting it had been replaced. (ENT: "Cease Fire")
According to the Star Trek: Star Charts, on page 60, Echo One was located in the Beta Quadrant.