[CW] Tone Modulated CW

[N2EY@aol.com]

In a message dated 9/14/02 3:26:41 PM Eastern Daylight Time, 
k4kyv@hotmail.com writes:

> Does anyone have any idea why the Liberty ships would have used tone 
>  modulated CW (type A-2 emission)instead of regualr CW?  I am aware that 
>  early tube type CW rigs would modulate the carrier using a rotary 
mechanical 
> 
>  chopper, but I always assumed this early MCW was used to make the signal 
>  readable on a diode or other detector in existing receivers that had been 
>  originally designed for spark.
>  
>  One advantage MCW would have had over regular CW (A-1) is that frequency 
>  stability would not be so cricical in reciver or transmitter.  However, by 
>  WWII, xtal control was the order of the day, and stable receivers were in 
>  common use.  One good example was the pre-WWII National HRO, which once 
>  warmed up, would stay on frequency on 20m. for hours at a time without 
>  needing to retouch the tuning.
>  
>  Does anyone have any ideas?

I think the main reason was so that the signal could be copied by any 
receiver without accurate tuning. In an emergency that could be the 
difference between life and death. A2 has long been a common mode in the 
maritime services. 

Sure, an HRO is stable, but the ships at sea back then were using a wide 
variety of equipment. Regens and TRFs were common on 600 meters. Look at the 
RBA!

73 de Jim, N2EY