There must have been some significant issues with that system because it was 
abandoned after a fairly short period.  Interestingly enough, AM radios made 
at that time actually had markings for the two frequencies 640 and 1240.

Steve


----- Original Message ----- 
From: "Martin McCormick" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, November 14, 2011 12:32
Subject: Re: A Bit of Radio History


> I do remember the CONELRAD tests.
>
> Radio and television stations would broadcast an
> introductory message as to what was about to happen. The carrier
> would go down for 15 seconds. Then, it would come back up for
> another 15 seconds. It was down for yet another 15 seconds and
> when it came back up, there was a 1 KHZ tone for maybe another
> 15 seconds. CONELRAD receivers had to detect the two drops in
> carrier plus the tone and that initiated the CONELRAD condition.
>
> My father was a science teacher at a school in Tulsa,
> Oklahoma at the time and had gone in to the teachers' lounge or
> maybe the school office for something and turned on the radio.
> He first thought the radio was broken because there were only
> two signals on the air. Then, he was reminded of the test which
> went for half an hour or so and then all other stations came
> back on and things were normal.
>
> I think the test was done every year for a while. I
> don't remember the first test, but the one in 1957 or 1958
> featured a talk by our state's governor at the time.
>
> I bet the station engineers loved this test if their
> station was one of the CONELRAD stations because they had to run
> all this stuff that you couldn't test any other time and it had
> to work perfectly this one day and, of course, be ready to
> switch in on a moment's notice.
>
> Tulsa had a 50,000-watt station KVOO at 1170 which was
> one of the CONELRAD stations so they had to electrically chop
> off part of their antenna to tune it up on 1240. I am sure this
> was accomplished by large contactors which are just huge relays,
> but still, when else could you make sure it worked?
>
> The other 50,000-watt station in Tulsa was KRMG at 740.
> I have no idea, for sure if they were the 640 CONELRAD station,
> but they would have had to add some electronic length to their
> masts to reach 640.
>
> It did work, however, so it just shows you what people
> do when they need to.
>
> Something else you might find interesting during those
> days was a plan to use AM broadcast transmitters as data links
> for RTTY and Morse.
>
> There was an article in "QST" several years ago about
> WSM 650 in Nashville TN. They actually had a FSK encoder on
> their 50-KW transmitter which shifted the carrier maybe 50 HZ
> and would have let them send RTTY to suitable decoders. An
> average citizen listening to WSM would have noticed nothing
> unusual. The article described the test transmission as a loop
> sending the call letters and the word "test."
>
> Lloyd Rasmussen writes:
>> I don't remember hearing any of those celebrity PSA's, but they aren't
>> very
>> different from what FEMA tells us today at ready.gov or other websites.
>