giving the pilot the opportunity to select any of the available channels with no need of changing a crystal. This is very popular in flying clubs where a lot of pilots have to share a limited number of channels. Latest receivers now available use synthesiser technology and are 'locked' to the transmitter being used. Dual-conversion radio receivers have been in existence since the 1980s and commonly in use since that time, which add security for the proper reception of the control signal, and can offer the advantage of a built-in 'failsafe' mode. Using synthesised receivers saves on crystal costs and enables full use of the VHF bandwidth available, for example the 35 MHz band. Newer Transmitters use spread spectrum technology in the 2.4 GHz, upper-UHF frequency band for communication. Spread spectrum technology allows many pilots to transmit in the same band (2.4 GHz) in proximity to each other with little fear of conflicts. Receivers in this band are virtually immune to most sources of electrical interference. Amateur radio licensees in the United States also have general use of an overlapping band in this same area, which exists from 2.39 to 2.45 GHz, with newer aftermarket transmitter RF module/receiver combinations on the 70 cm band also offering user-programmable, spread-spectrum versatility of varying degrees for Ham RC modelers in both the US and Canada, only as secondary users without "exclusive" use provisions. Military usage Radio-controlled aircraft are also used for military purposes, with their primary task being intelligence-gathering reconnaissance. An Unmanned Aerial Vehicle (UAV), also known as a drone, is usually not designed to contain a human pilot. Remotely controlled target drone aircraft were used to train gun crews. Regulations on use Various countries have regulations and restrictions on model aircraft operations, even for non-commercial purposes, typically imposed by the national civil aviation authority. United States In the United States, radio-controlled model aircraft and unmanned aircraft generally may be subject to regulation by the following entities: Federal Aviation Administration The legal status of radio-controlled model aircraft under federal aviation law is currently unclear. In March 2014 in the case Huerta v. Pirker, an administrative law judge with the National Transportation Safety Board (NTSB) dismissed an FAA enforcement action against a model aircraft operator under 14 CFR 91.13 (prohibiting careless and reckless operation of an aircraft), ruling that model aircraft are not legally classified as "aircraft" and that they are not subject to