We’ve previously written about the NEAR system, which was a system envisioned to alert the American public to a nuclear attack. It relied upon a 240 Hz signal superimposed upon the power lines. This signal was picked up by an ingenious electromechanical receiver in the home, and sounded a loud buzzer in the event of an alert. We previously described how the receiver worked, and the August 1960 issue of Popular Electronics, from which the pictures above were taken, explains the equally simple method used to transmit the signal. In the schematic at right, at the utility substation, to send the alert, switch S1 is opened. The rectifier sends a flow of DC pulses through the transformer secondaries, generating a signal at the fourth harmonic of the power line frequency. This signal averaged about 2-3 volts, meaning it would not interfere with regular power transmission.

On that October day, the alarm originated at a radar station in the Arctic, from which it was relayed to NORAD headquarters in Colorado Springs, CO. An officer there pushed the button to activate the NEAR system, resulting in the alarm being sounded almost immediately in Charlotte, MI.

That morning, seniors at the high school, the Charlotte Class of 1961, had inflated weather balloons and distributed them around town. When the devices buzzed in each home, homeowners were to release the balloon on a tether. Back at the courthouse, the students were in the tower of the courthouse counting balloons.

References

• Charlotte History: NEAR Testing
• Charlotte Republican-Tribune, Oct. 13, 1960
• Popular Electronics, Oct. 1961

This year marks the 70th anniversary of the Great Flood of 1951 along the Kansas and Missouri Rivers. With 17 deaths and almost a billion dollars in damage, the flood was the nations then-costliest natural disaster.

The photo above shows downtown North Topeka, Kansas, from the July 30, 1951, issue of Life magazine.

According to the November 1951 issue of QST, much of the Amateur Radio response to the flood focused around the U.S. Naval Reserve. Station K0NRZ at the Naval Reserve Training Center in Topeka maintained a continuous watch on local emergency frequency 29.5 MHz from July 11 to 15. On the 15th, a long-haul net was established on 7042 kHz and handled over 1000 messages through July 20.

One ham reportedly furnished handie-talkies (3885 kHz) which were used for communication between Army/Air Force trucks and Coast Guard boats engaged in sandbagging the levees.

The QST October issue also reported that the station K0NAB at the Naval Air Station in Olathe, KS, handled radio traffic for Western Union, whose lines were out.

This young woman shown above in Popular Mechanics 70 years ago this month, June 1951, is using her portable radio to pull in some entertainment at the beach. But she also realizes that in a civil defense emergency, the set might have a vital role to play if the bombs started falling.

The problem, of course, is that you need batteries for the radio, and many sets had oddball shapes and sizes, some of which might not be available in the runup to an emergency. Therefore, the magazine gives some pointers on substituting what’s available. Even though the batteries might not fit in the case, with a little thought, it was a relatively easy matter to power the radio for emergency information.

Shown here, on the cover of the May 1951 issue of QST is ARRL’s then-National Emergency Coordinator, George Hart, W1NJM, operating a portable 6 meter civil defense portable station designed by Ed Tilton, W1HDQ and described in the magazine.

Tilton’s article described the design goals of the set. He noted that in the past, emergency gear almost always meant “rigs with handles,” namely equipment that could be operated on a 6 volt battery or small AC supply. While such rigs were the backbone of WERS during World War II and would continue to occupy a prominent place, the “present emergency” brought a new need, namely, communications for the radiological survey team. Those teams required on-the-spot communications with a transmitter-receiver that could go with an operator on foot, and not tied to a car battery or other power supply.

The choice of bands to be used presented some problems. A simple modulated oscillator (such as the one described in another magazine the same month), would eliminate the expense of crystals, but they were really practical only on the 220 MHz band, since the civil defense frequencies assigned on 2 meters were two narrow a range for such a transmitter. On 6 or 10 meters, however, crystal oscillators were more cost effective, and between the two, 6 meters allowed a shorter antenna. Therefore, the choice boiled down to 6 meters, if crystal control was desired, or 220 MHz, if it was not. The circuit shown here was a crystal-controlled transmitter-receiver for six meters.

The transmitter used a 3A5 dual triode. The first half was a 25 MHz oscillator using 8.4 MHz crystals on their third overtone, or 25 MHz crystals. The second half of the tube served as a doubler. The set could also be used on 10 meters with different crystals, and using the second half of the tube as an amplifier rather than doubler. A 3Q4 was used for modulator. The superregenerative receiver employed a 957 acorn tube detector, with another 3Q4 serving as audio amplifier.

Since the author couldn’t find another suitable carrying strap for the rig, a piece of 300 ohm twin lead was pressed into service.

Seventy years ago this month, the May 1951 issue of Radio News carried the plans for this 220 MHz transceiver designed for civil defense use. The band was chosen because of it was authorized for use by holders of the newly minted Technician license. With many younger hams being drafted, it was thought that opening up opportunities for Technician class hams would be a way to bring in the operators that were urgently needed for civilian defense operations.

The main design parameter for the set was to provide reliable communications over a 5 mile range. This would be sufficient to cover a small town, or, in the case of a larger city, one police precinct, upon which civil defense operations were often based. Lower bands could be used for inter-city communications, freeing up units such as this for use in local emergencies.

The heart of the circuit was a 955 acorn tube, with more common miniature tubes (6J6, 6J5, and 6V6) rounding up the circuit. The 955 operated as a superregenerative transceiver. The tuned circuit used off the shelf components, but the capacitor required some modification to cover the entire band. If a frequency meter were not available, the magazine noted that in a TV with a 21 MHz IF, the set’s local oscillator would radiate on 225 MHz, allowing calibration of the transceiver. An additional hint in areas with a channel 13 TV signal would be that if the TV station were audible, this meant that the transceiver was tuned too low.

The author reported good signals over a 17-mile path with the set, meaning that for its intended use of 5 miles, the two watt set would likely perform well.

Seventy years ago, this gentleman was pulling in a program on the standard broadcast band with headphones, but in the following months, he would be able to listen to the shortwaves with loudspeaker volume. He is shown here listening to the first iteration of a progressive receiver featured in the May 1951 issue of Popular Mechanics. In coming months, additions would be made to the set to allow shortwave reception and loudspeaker operation.

The set was battery powered, and the magazine pointed out that there were a number of good reasons for putting together a battery set. The most important reason was having a set capable of operation independent of the power lines for civil defense purposes. The circuit was also simpler and saved having to deal with baffling power supply troubles.

This version of the set used a 1U4 tube as regenerative detector followed by a 3V4 audio amplifier. An indoor antenna and ground could be used for local statioms, but an outdoor antenna would be best for long distances. “With a battery-operated emergency receiver of this description, you are not cut off from outside news and vital civil-defense information should local power sources fail. Most of us do not realize how important this could be.” You would, of course, need to keep fresh batteries on hand. The circuit called for flashlight batteries for the filament, and a 45 volt battery supplying the B+.