Lopaka said:
Speaking of Conelrad...why did the authorities decide on 640 and 1240 for the alert frequencies? 1240 makes sense, so many locals on that frequency, but 640? And what authorities made the decision?
The channels were decided on because they were, on the radio dials of the day, equally spaced and between the usual dial markers. Dials back then had as much spacing for 540 to 900 as 900 to 1600 in many cases, and the marking might have been 550-600-700.... 1200-1400-1600. In other words, it was fairly arbitrary but designed to let the triangular conelrad logo fit into dial plates of the time, I believe.
There were three or four CONELRAD tests... two nearly consecutively (coupla' months apart) in the late 50's and two more in the early 60's that I remember... all AMs off air except those that went intermittently on one of the two emergency frequencies. In fact, from NE Ohio, I heard Canadian stations as far away as Winnipeg and Regina at the mid-day test time! It appears that the two in the 50's were considered one test by the authorities, though.
About 20%, IIRC, of all AMs were part of CONELRAD. They had to tune to one of the two frequencies and in most areas, 3, 4 or 5 signals would alternate for a minute or two each. The idea was to not allow a missile to home in on a single signal; many still remembered that KGU had been used as a homing beacon for Pearl Harbor. So rapid switching, only two immensely congested channels and very low power was intended to thwart any homing.
Low power was a necessity, as moving a transmitter from its licensed channel to another without extensive retuning can burn it to a crisp... in some cases, the moves were 400 kcs, so only very low power would work, even though some transmitters had a test mode for this purpose.
If you search the Broadcasting Magazine section at
www.americanradiohistory.com on CONELRAD you can come up with lots of data if you are curious. Every issue of the magazine from that era is available and searchable.