Note
CONELRAD is a portmanteau for CONtrol of ELectromagnetic RADiation. The CONELRAD system was designed to thwart attempts by enemy missiles or aircraft to home in on broadcast stations. (This was how the Japanese found their way to Pearl Harbor.) The assembly manual rather matter-of-factly states that having the CA-1 connected to your transmitter “precludes the possibility of your station being the recipient of a guided missile which is using your antenna for a homing device.”
The CONELRAD system was established in 1951 and used a crude signaling system to alert broadcast stations to go off the air. Had it become necessary to activate the CONELRAD system, key AM broadcast stations were to cycle their transmitters off and on for a few seconds at a time. All other broadcast stations monitored the key stations with special equipment that sounded an alarm if the key station carrier disappeared. These stations would then cease broadcasting until further notice.
Beginning in 1957, amateur radio stations also were required to cease operation if CONELRAD was activated, and the CA-1 uses this same signaling system so alert amateur radio operators.
The CA-1 is placed in the line between the 120 volt mains and equipment to be controlled. It was then attached to any AC or DC broadcast band radio, provided the radio had an AVC. When the monitored broadcast station went off the air as previously described, the CA-1 would cut power to whatever was plugged into the front panel receptacle, and would light a red warning light.
The CA-1 uses a 2D21 thyratron, a 6-amp relay, and an internal power supply. The front panel contains an on/off toggle switch, a “reset” push button, a pilot light (clear), an alarm light (red), a sensitivity control and a 120 VAC two-prong outlet. Note that the two panel lights are of different styles. The rear panel contains the line cord and a cable for connection to the receiver. The unit is finished with silver and gray paint and matches the DX series and other small accessories.
Although deleted from the catalog after 1960, the CA-1 appeared once more in a discontinued-item sale flyer mailed in April 1962.
Caution: The CA-1 uses a fused power plug. The power supply does not include bleeder resistors.
References:
Brief description. Radio News, Jul 1957, p. 126.
Conversion to a ten-minute timer. Ham Radio. Jul 1968, p. 74.
AVC sensitivity: –2 to –20 volts
Power requirements: 120 VAC, 60 Hz, 7 watts
Power capability: 120 VAC, 60 Hz, 700 watts
Tube: (1) 2D21
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
