The Thunderbolt siren is a warning siren that was once manufactured in the United States by Federal Signal Corporation. The Thunderbolt siren consists of three major components: the blower, rotator and siren chopper. The blower, which is made up of a motor-driven Roots-type supercharger, supplies the large volume of air for the siren head. It is housed inside a large rectangular box typically found at the base of the siren head. The blower is connected to an air standpipe which pumps 250 cubic feet per minute of air at 6-7 psi up to the siren head. The rotator is a motor-driven gear unit which rotates the directional horn/projector to direct the sound in all directions. The chopper is located in the cylindrical housing that the horn/projector attaches to at the top of the siren. The siren chopper motor in the Thunderbolt siren is actually the same siren motor used in the Federal's Model 2 siren. The siren chopper in the Thunderbolt operates in the same manner as any conventional siren. As the chopper rotor spins air pulses are generated by the rapid opening and closing of the chopper openings. This generates the sound the siren makes. The primary difference in the Thunderbolt siren is that the air supplied by the blower is pumped through the siren resulting in a greatly increased sound volume and distinct sound generated by the Thunderbolt siren. The Thunderbolt siren is operated by a control panel called an RCM Panel. This panel consists of the three relays that switch the three components of the siren on and off. The RCM panel also has a time delay relay and circuit. This time delay section keeps the blower and rotator operating in the attack signal while the siren chopper motor is switched on and off which produces the up-and-down pitch of the attack signal. With the blower and rotator operating as the siren motor is switched on and off the Thunderbolt maintains a high level of sound output. An additional important feature of the RCM panel is a transformer in the siren/chopper electrical circuit. This transformer has seven different voltage taps from 120 volts up to 240 volts. This allows the top pitch of the siren to be changed as desired when the siren is installed. A siren with the chopper connected to the 120volt transformer tap will sound at a lower top pitch than a siren connected at the 240volt transformer tap