Chopper Rotator


Siren Controls

Sirens Main
Civil Defense
Museum Main
Civil Defense Museum

The original Thunderbolt siren intallations used a fairly elaborate set of electro-mechanical controls for operation. Since the Thunderbolt has 3 motors it used what was called an "RCM" cabinet with 3 motor starters to operate it. The Thunderbolt 1003 used a second motor control panel, and RCM 3, in addition to the RCM panel. The RCM 3 controlled the Hi-Lo solenoids for the 1003 siren. For signal timing on Federal Sirens the Federal AR, AF or PGA timer were used. Though the timers weren't exclusive to Thunderbolt siren operation I cover them at the bottom of this page. Federal timers could have been used on all their models of warning sirens.

The first Thunderbolt I restored didn't have an RCM panel with it when I got it so I used a panel that was salvaged from an early-mid 1970s model Thunderbolt. (shown below)

This is a Federal Signal RCM1A cabinet which is equipped with 3 motor starters (relays). The 3 greenish colored components are the motor starter contacts. The starter activation coils are just below the contacts. These starters allow switching of the high current to the various siren motors by a lower current switching contol circuit. The silver and black "AGASTAT" component in the center of the panel is a time delay relay. This time delay relay keeps the rotator and blower motors activated while the chopper starter turns on and off during the attack (wavering) signal. With the blower activated during the up and down portion of the chopper cycle the sound output of the Thunderbolt is kept at a high volume during the entire cycle due to the high volume of air being forced through the siren chopper. This was Federal's main design goal with the Thunderbolt; to keep it loud through the entire signal. The larger transformer at the lower right of the panel controls the pitch of the chopper motor. (see below for more details)

The RCM1A is used with the Thunderbolt siren when the siren is operated from a 3 phase power source. The RCM1B is used with a single phase power source. This RCM1A is the control panel I restored for my Thunderbolt restoration. Other versions of the RCM panel are very similar to this panel. The line input power connects to the larger terminal block at the top left of the panel. The rotator connects to the far left bottom terminal strip, the blower connects to the large terminal block at the bottom center of the panel and the siren chopper connects to the terminal strip at the bottom right of the panel below the large transformer. I cover the different versions of the RCM panel below. Click image to see larger.

Chopper Pitch Control and Test Switch Panel

Here is a close-up of the chopper hook-up terminal strip, chopper auto-transformer and test switch panel. The most unique features of the Thunderbolt siren was the ability to change the sound pitch of the siren. This was done by connecting the siren chopper to one of a series of output voltages. The pitch of the siren can be changed by hooking up the chopper to the various terminal strip terminals. One wire of the chopper motor is connected to the far left terminal. The pitch is lowest when the other wire to the chopper is hooked up to the terminal second from the left and the pitch is highest when the other chopper wire is hooked to the far right terminal. This set up varies the voltage to the chopper from 120 to 240 volts. The lower voltage being the lower pitch and the higher voltage being the higher pitch. The last version of the RCM had the chopper output voltages marked on the transformer output wires.

The test switch panel at right in the photo allows each motor of the siren to be operated individually. Moving the respective switch to the test position manually activates that motor. When all the switches are at the Automatic position then the RCM panel is controlled by a switched signal (siren control timer) connected to the "control" terminal strip at the upper right of the panel.

Early Federal Signal Siren AR and AF Timers

This timer is the early version of the Federal AR timer. The Federal timers used timer motors which operate a system of cam-operated switches to activate the siren signals for a 3 minute cycle. The type of timer pictured at right was sold by Federal up through some time in the 1960's. I base this on a drawing in the early issue of the Thunderbolt siren manual that shows siren hook-up wiring diagrams. The date on this drawing is 1968 and it shows the newer style siren timer. (shown below) The timer pictured was installed in Dallas Texas in 1959. The box measures W12.5 inches x H9.5 inches x D6 inches. The red lamp above the buttons activates only when the timer is cycling. The top button on the front panel is the "Manual" button which operates the siren for only as long as the button is depressed. This is the same function as the "test" button used on later model Federal timers. The second button from the top is the "Take Cover" signal which operates the siren in a on-off or wavering mode for 3 minutes. On later timers this function button is labelled "Attack." The bottom button is the "Alert" signal which operates the siren in a steady "on" mode for 3 minutes.

This is the inside of the early version of the AR timer pictured above. You can see in this picture that the timer uses adjustable switch levers which are activated by a series of cams moved by the timer motor. The purple wires at the bottom are connected to the power input terminals of the terminal strip. This timer operates on 230 volts. The Federal electro-mechanical timers are simply timed switches. They don't output any power so it's not possible to power a siren or relay from the timer itself.

This is an early Federal AF timer. The timer box is the same size as the AR timer pictured above but the AF timer has the added mode to operate a "Fire" signal. The Fire signal was used on the Federal Thunderbolt 1003 and Federal 3T22 sirens for the option to use a Civil Defense siren as a volunteer fire department call-in siren. The fire circuit in the AF timer would activate a cycling switch in the RCM 3 control cabinet (Thunderolt) or the RC6 (3T22) which would operate the Hi-Lo signal of the siren. An explanation of the fire signal operation is shown on the fire signal page.

Inside the early AF timer is pretty much identical to the early AR except for the additional cycle cam wheel, switch, extra push button and relay fpr the fire signal. The switch levers with rotary cams beneath are a bit easier to see in this photo. The timer motors in these early timers are 120 volt and the voltage is reduced with a large load resistor. The resistor is the brown tube-like component next to the timer motor in the AR and AF timer inside photos.

Later Federal Signal Siren AR and AF Timers

This is the later version of the Federal AR timer. Federal Signal no longer sells this timer. When they did the price was about $1500. This particular timer has NOV 1986 stamped inside. The box measures W8.5 inches x H10.5 inches x D4 inches. The yellow lamp on the front of the box operates as long as the unit has power and the red lamp operates when the timer is cycling. This timer has the same functions as the early timer but the front panel is quite a bit different. The silver button on the front panel is the "Test" button which, like the "Manual" button on the early timer, operates the siren for only as long as the button is depressed. The blue button is the "Alert" signal which operates the siren in a steady ON mode for 3 minutes. The yellow button is the "Attack" signal which operates the siren in a on-off or wavering mode for 3 minute signal. The black button is the "Cancel" button which stops the timer's control of the siren signal while the timer continues to run to the end of it's cycle. The early timers didn't have this feature.

For more in-depth information on these timers I have the Federal instruction sheet for the later siren times available for download here... Instructions For Models PGA, AR, AF, AR5 and AF5 Timers.

The inside of the later Federal AR timer is quite a bit different but the same principal as the older AR timer but with newer more compact components. The later timers used smaller rotary cams and microswitches instead of the much larger lever switches. A transformer was also added so the timer could be connected to 120 or 240 volts. These timers could also have transformers in them for connection to high voltage supply.

Like the early AF timer the later AF timer has the added "Fire" button on the front. The "Fire" signal would be used as a fire call signal for volunteer firefighters. The fire signal is similar to the attack signal in that the siren turns on and off resulting in the up and down signal but also produces a "Hi-Lo" signal while the siren is powered during the on portion of the on-off cycle. When the siren runs in the off portion of the signal the Hi-Lo stops and the siren coasts down regularly. The Federal Thunderbolt 1003 and the Federal 3T22 were both capable of producing the fire signal. An explanation of the fire signal operation is shown on the fire signal page.

This timer is pretty much the same as the AR timer above but has an additional motor-driven cam and relay to operate the fire signal. The hook-up schematic is missing from this unit.

Federal PGA Timer

Federal also made a PGA timer which stands for Predetermined General Alarm. This is the description from the Federal timer instruction sheet. The PGA (Predetermined General Alarm) is primarily used for general alarm sirens, allowing them to sound an up and down scale wailing signal for a predetermined time. The standard PGA timer produces a timing of 8-seconds ON, 4-seconds OFF; repeated 10 times in a two minute cycle. I don't know how long Federal made the PGA. The date on this timer is AUG 23 1974.