E11 was first reported in early 1980s. It became known for very little actual traffic, only sending null messages for years. This only changed in mid-2000s.
Originally a different voice was used, also featuring Polish accent. The current voice started in 1990.
E11a's old voice. Recorded on June 6th, 1988. Recording courtesy of Numbers & Oddities.
Since September 2002, E11's audio comes from a PC. The old transmissions had better voice clarity than now.
E11 in 2000, before digitization. Recording courtesy of Simon Mason.
In 2003 - 2009, a variant E11b existed, which included the group "77777" as the first, second, last but one, and the last group of the messages.
Notable increase in activity of E11 was during September and October 2007, with daily messages of large amounts of groups.
Prior to June 1st, 2008, the null messages and message intros were 5 minutes and 20 seconds long, rather than the current 3 minutes and 20 seconds.
In 2010 - 2013, a variant E11c existed, which was a special null message format on its own, separate schedules.
Up until mid-2013, E11 was frequently, but not always, observed with audio of bad quality, with distortions and/or background buzzing.
Distorted E11a transmission. Recorded on August 23rd, 2011 at 12:40 UTC on 6252 kHz.
From April to August 2014, E11 was notably frequently observed with Windows XP shutdown sounds following the last schedule of the day, but not always.