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Re: Conelrad question

Your idea would have totally defeated the purpose of 
Conelrad, which came about after it was reported that 
the Japanese planes that attacked Pearl Harbor had used 
commercial AM broadcast signals to home in on Honolulu. 

AM stations in a market were divided into two groups by 
frequency. Those above the middle of the band were 
assigned to 1240 and those at the low end were assigned 
to 640. All were supposed to transmit nondirectionally 
and, I believe, none was allowed to use more than 5 kW.

The signal to each of the transmitting antennas was 
keyed on and off for a few seconds at a time in a quasi-
random pattern by a signal sent (via land lines, I 
believe) from Civil Defense headquarters. The idea was 
that because the time-division-multiplexed transmitters 
were geographically dispersed (in Boston, for example, 
640 originated from Medford (590), Burlington (680), 
Cambridge (740), Saugus (850--moved to Needham in 1948), 
and Saugus (950--after 850 moved to Needham), the radio 
direction finders would be confused. Allegedly the 
needle on the radio "compass" was supposed to spin 

The idea had a lot of holes in it. While I was in 
college, I heard one test in the Albany NY area. Four 
stations alternated on 640--590, 810, 850, and 980. (850 
has been dark since the early '50s.) On 1240 there were 
four others: 1240, 1400, 1460, and 1540. The number of 
stations on both channels was inadequate and there was 
no signal at all in some time intervals. The result was 
that the signal was barely listenable and if important 
civil defense info had been broadcast, a lot of people 
would not have been able to make it out.

Moreover, in many smaller markets, there would not have 
been enough stations to populate the two frequencies. 
And the use of insecure land-lines to send both the 
program and the keying signals seems laughable in the 
context of a national emergency. After all, in those 
days people were building fallout shelters deep 
underground. Many people would probably have suffocated 
if they ever had to use those shelters, but they knew 
that the telephone lines above ground would not 
withstand a nuclear attack.

Also, I have my doubts about the ability of the system 
to prevent the use of radio signals for navigation.

> Some of us are old enough to remember the old Conelrad(sic?) that predated
> the EBS notification system. The emergency info would be transmitted at
> either 640 or 1240 or the AM dial and all other stations would go off the
> air.
> So...how exactly was this done....was there a special high power non
> directional transmitter somewhere in Boston on 640/1240  and how was this
> supposed to work in non urban areas?