Spektrum is a new radio system, from Horizon Hobby. The Spektrum radios are 2.4 GHz DSM, instead of the usual 75 MHz currently in use. The transmitters use a plastic antenna, which contains a short antenna wire and folds down to the side, instead of a metal telescoping antenna. The reciever antenna is a standard wire antenna, but is very short, and can be cut slightly shorter. While the antenna does not need to stick out of the body, it can be used with an antenna tube in the standard configuration, at a more scale appearing length, on some models. Often it is simply used with an antenna tube that is short enough that it does not need to stick out of the body.
Spektrum does not use any type of conventional RC channel. Nothing needs to be done to get it on an empty channel, it automagically figures out a channel it can use. These channels do not conflict with any standard radio systems, because of the 2.4 GHz frequency band.
The DX3 is the first standalone Spektrum radio system. It's based on the JR XS3. Unfortunately, it only has three model memory, and models can only have a three letter name.
The DX3 has a notable new steering mix feature, which did not exist in the XS3. This allows you to use dual steering servos, on seperate channels, and mix them together, without using a servo cable splitter. This can only be used if you do not need the third channel for a seperate function.
Spektrum modules are available to upgrade several radios commonly in use. These allow you to use Spektrum with several popular radio systems, with the equipment you might already own, at a lower price then a complete radio. These modules have the small plastic Spektrum antennas integrated into them.
The creators of Spektrum at Horizon Hobby have developed a telemetry link, the first of its kind in radio control. It shows engine RPM, temperature, battery voltage and other operating parameters on a handheld device that can be attached to the empty antenna hole that a Spektrum upgrade leaves.