Logic Trunked Radio (LTR) is a radio system developed in the late 1970s by the E. F. Johnson Company.
[1] LTR is distinguished from some other common trunked radio systems in that it does not have a dedicated control channel.
Typically on LTR systems, each of these controllers periodically sends out a data burst (approximately every 10 seconds on LTR Standard systems) so that the subscriber units know that the system is there and which channels are in use or available.
The idle data burst can be turned off if desired by the system operator.
To a listener, the idle data burst will sound like a short blip of static like someone keyed up and unkeyed a radio within about 1/4 second.