A HyperWave Broadcaster or Caster for short is a device capable of communication and detection at great distances using HyperWaves, perturbations in the HyperSpatial medium detectable from TrueSpace, that travel at superluminal speeds from a TrueSpace perspective and allow near-instantaneous communication through the HyperSpatial frame of reference from within TrueSpace.
Though HyperWave transmissions are much more robust than electromagnetic transmissions through TrueSpace or HyperSpace, they can be jammed by transmissions on the same frequency, blocked by force fields like an Ur-Quan slave shield (though a very sensitive receiver, such as those contained naturally within Chenjesu bodies, can detect transmissions from inside a slave shield if the transmission is sufficiently powerful) and tend to lose coherence and dissipate over long range.
Aside from the very subtle ability to detect and transmit HyperWave that evolved naturally within the Chenjesu's crystalline biology, which other species have been unable to reproduce, all spacefaring species use essentially the same principles in HyperWave communication and detection, usually discovered independently near the beginning of a species' atomic age, with some exceptions (such as the Humans). HyperWave Casters tend to be relatively large, expensive pieces of equipment and are therefore standard for planetary or orbital installations but rarely seen aboard all but the largest starships; most ships tend to restrict themselves to communication using ordinary electromagnetic radiation.
HyperWave energy has many interesting properties that make it useful for a number of functions. HyperWave receivers can be used to monitor transmissions in the ordinary electromagnetic spectrum, which leave "shadows" as HyperWave perturbations that travel at superluminal speeds -- this allows intraplanetary communications to be monitored from a distance. Similarly, the passage of starships through HyperSpace leaves HyperWave ripples that can be passively detected from a distance and analyzed in order to track starships from farther away than the visual range by which they can be detected by electromagnetic scanning within HyperSpace.
Most high-power HyperWave Casters broadcast on certain predetermined frequencies or channels within a limited range, sending out programming from various stations for information, advertising or entertainment. This practice ended in many parts of local space after the invasion of the Ur-Quan Kzer-Za and Kohr-Ah made it extremely dangerous for a species to broadcast its location.