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A subspace channel was a communication channel consisting of a designated band of subspace frequencies, or single dedicated subspace

According to Spock, as of 2267, beyond the region of Cestus III existed only "rumors of certain strange signals on subspace channels. However, none has ever been recorded." (TOS: "Arena")

Lore transmitted on a subspace channel from aboard the USS Enterprise-D to contact the Crystalline Entity in 2364. (TNG: "Datalore")

Data later blocked every subspace channel after he had commandeered the USS Enterprise-D in 2367, making it impossible for the rest of the crew to call for help. (TNG: "Brothers")

In an later effort for Captain Jean-Luc Picard to locate the rogue USS Phoenix, he had Worf transmit priority one communique that contained "a repeating message on all subspace channels" for the Phoenix to "Break off your pursuit immediately." (TNG: "The Wounded")

Later yet that year, Picard once again had Worf transmit another priority one communique that contained "a repeating message on all subspace channels" that ordered Lieutenant Paul Hickman aboard the Federation shuttlecraft to "come about and stand to." (TNG: "Identity Crisis")

A convoy of Vulcan ships that crossed the Romulan Neutral Zone responded to a subspace message from the Enterprise-D that stated their intentions, and that further requested that the Enterprise "monitor Federation subspace channels," as "Ambassador Spock will be making an announcement shortly." When it was transmitted a short time later, the announcement came in "from Romulus on all subspace channels." (TNG: "Unification II")

Due to the sensitive nature of the mission the USS Enterprise-D was assigned to, following their rendezvous with the USS Crazy Horse in 2370, Vice Admiral Margaret Blackwell explained to Captain Picard that she preferred not to discuss the matter over subspace channels. (TNG: "The Pegasus")

The same year, the Miles O'Brien replicant requested the runabout's computer to open a subspace channel to Starbase 410 to send a priority one message to Admiral Rollman. (DS9: "Whispers")

List of subspace channels