[Hallicrafters] S27 and EBS

[Roy Morgan]

At 04:23 AM 3/24/2004 -0800, you wrote:
>Hello to all.
>  Does anyone have any knowledge of the old Civil
>Defense Emergency Brodcast System?


HAH! Maybe most folks are to young to remember..heheh

here is what I remember:

The system worked based on these basic ideas:
  - all broadcasting radio stations had a way be be alerted if a warning 
came along.
  - If an alert was issued and stations were to shut down they broadcast a 
set message with tones to alert the listener, then shut down.
  - a few authorized stations on 640 and 1240 KC were to continue 
broadcasting and give out information to the population.  (The idea was to 
reduce the many stations that could be used for missile or aircraft 
homing/navigation to a minimum)

The Conelrad monitors (such as the one Heath made) or monitor radios, which 
you may have one of, were set up with an AVC detector and an alarm circuit, 
and in the case of the Heath unit, a relay to de-energize your transmitter. 
When the station to which you had tuned your monitor went off the air, the 
AVC in the receiver would go away and light the warning lamp and turn off 
your transmitter.

>   I suspect the transmitter was what we used to hear
>when the Conelrad EBS was tested, just a tone on the
>CD freqs.

I don't know what use the transmitter you have would have been at a radio 
station.. it was likely owned by a ham. It may have been modified with a 
relay to shut it off when the CD monitor radio sensed no carrier on the 
local station.

The tone and announcement were broadcast over the normal station frequency 
and equipment.. in the event of an actual alert, the station would then be 
taken off the air (unless it happened to be one of the 640 or 1240 kc 
designated broadcast stations.)  the CD triangle on radios were there to 
help citizens tune their radios to the right frequency to receive further 
information and instructions.

Roy
Who was a kid during those times.

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
roy.morgan at nist.gov --