[IRCA] Synchronized transmitters, 1939 style (WBBM and KFAB)

[Deane McIntyre <dmcintyr@xxxxxxxxxxx>]

I came across this interesting article online, from the June 1939
issue of Mechanix Illustrated:

<http://blog.modernmechanix.com/2006/02/28/delaying-the-broadcast/>

It seems that at this time WBBM and KFAB were synchronized on
770 kHz, with the KFAB audio being fed from WBBM. The problem
of the transmitter frequencies having to be identical to avoid  
heterodynes
seems to have been easily solved, however by the time the audio
arrived at KFAB it was delayed by 23 milliseconds. Thus, in the
area that received both signals the audio had a "hollow" sound.
Solution: delay the audio fed the WBBM transmitter by 23 ms.
How to do this with 1939 technology? Use 23 feet of lead sewer
pipe stuffed with fabric etc as a delay line, with a speaker
at one end and a microphone at the other! Interesting reading.

73,

Deane McIntyre VE6BPO
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