Defend an Encoder and a Transmitter against a large horde of aggressive EXALT agents in a King of the Hill-type scenario until all enemies are eliminated.
EXALT communication relays will be scattered across the map. There are usually 3-4 relays, depending on the size of the map. When the Covert Operative is moved next to one of these relays, Bradford will remind the player that these relays can be hacked to reduce EXALT agent capabilities.
EXALT agents will prioritize hacking the Encoder and the Transmitter over attacking XCOM forces. If they do not have a unit in the Encoder or Transponder capture zone, their agents will often dash towards it, using both moves if necessary to do so. This can provide a good opportunity to dispatch them.
The Encoder can be destroyed by explosives. Counter to what might be suggested by Central's briefing, this does not in fact make it impossible for EXALT to locate the Transmitter but instead makes it their immediate secondary target for occupation.
An adjacent vehicle exploding will not destroy the Encoder.
Any progress EXALT makes on the hacking the Encoder or the Transmitter cannot be reversed so be extremely cautious about how long you leave either objective uncontested.