1961 Operation Alert CONELRAD test

Operation Alert 1961 was a full on-air test of the CONELRAD system in which all radio and TV stations either went off the air or switched to transmit emergency information on either 640 or 1240 kc in a round-robin fashion to minimize the chance for an enemy to use their signals for homing purposes.   This video includes the entire 1/2 hour test from the New York City area, including a nationwide broadcast by President John F. Kennedy around 13 minutes in.

As hams, we wonder how the frequency change was made, and what provisions were made for quickly re-tuning the transmitting system.   Note the comment that stations on 640 or 1240 may be operating on reduced power, thus may be weaker than normal. Per this article that appeared  during the early planning phase of the Key Station System which turned into CONELRAD, the cost of implementing 640 or 1240 kHz transmitting capability fell to each individual station owner.

https://www.radiomuseum.org/forumdata/upload/conelrad_sys_def.pdf

The alternative was to leave the air (unless they were "drafted" by the
FCC). I've seen references to setting up a back-up transmitter with
CONELRAD capability, and since non-directional transmission was required on
640 and 1240, some stations used separate auxiliary antennas when in
CONELRAD mode. Thanks to the excellent search capability of the
WorldRadioHistory website I've read a number of references describing how
crystal switching and re-tuning components were relay-switched in
transmitters including the RCA BTA-1R1, using either a front-panel switch
or the stations regular remote control equipment.

Here is a brief outline of how CONELRAD alerting network operated, per an
FCC document created during the "Informal Government - Industry Technical
Conference" on March 26, 1951:

"The primary plan for alerting broadcast stations that is currently being
considered by the FCC Study Group is known as the Key Station System. The
arrangement requires certain telephone circuits (private wire or direct
line to Toll Board) between the Air Defense Control Centers (A.D.C.C.) and
specified radio stations to be known as "Basic Key Stations". Additional
telephone circuits (direct line to Toll Board) will be required in certain
cases, between "Basic Key Stations" and other stations to be known as
"Relay Key Stations". Each "Basic Key Station" receiving an alert or
warning signal from the A.D.C.C. shall, if so directed, proceed to
broadcast a predetermined message and also relay the message by telephone
to all "Relay Key Stations" under his control as specified." CONELRAD was
officially introduced on December 10, 1951.

CONELRAD had a simple system for alerting the public and other "downstream"
stations, consisting of a sequence of shutting the station off for five
seconds, returning to the air for five seconds, again shutting down for
five seconds, and then transmitting a tone for 15 seconds. Key stations
would be alerted directly. All other broadcast stations would monitor a
designated station in their area.

In the event of an emergency, all United States TV and FM stations were
required to stop broadcasting. Upon alert, most AM stations shut down. The
stations that stayed on the air would transmit on either 640 or 1240 kHz.
They would transmit for several minutes, and then go off the air and
another station would take over on the same frequency in a "round robin"
chain. This was to confuse enemy aircraft who might be navigating using
Radio Direction Finding. By law, radio sets manufactured between 1953 and
1963 had these frequencies marked by the triangle-in-circle ("CD Mark")
symbol of Civil Defense."

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The above carrier drop sequence was detected by CONELRAD receivers in radio
stations and by other licensed radio services, including hams.