[BC] Analog AM bandwidth: tail wagging the dog?

[Jim Tonne]

> 1450 WCTC takes the approach of transmitting C-Quam AM Stereo with full
> 10 kHz NRSC audio, but rolling off the pre-emphasis above 6 kHz, so that
> a plot of their pre-emphasis would curve upwards, reach its peak (likely
> 10 dB) at 6 kHz, and then curve downwards, reaching 0 dB at just below
> 10 kHz where the NRSC filter brickwalls.

That is absolutely not a gentle pre-emphasis.  To
boost 10 dB at 6 kHz is noticeably beyond the NRSC
curve.  If it reaches a peak at 6 kHz and is back 
down to 0 at 10 kHz it is not "gentle."

The NRSC curve   *IS*   gentle.  It is +3 dB at 2120
Hz, just as with FM.  But the total amount, the limit, as 
it were, is only 12 dB.  Indeed, the departure (3 dB 
difference) from an ideal curve is right near 8700
or so Hz.   It is up 7.4 dB at 6 kHz and up 10 dB at
10 kHz.

A pre-emphasis mechanism with a peak of 10 dB
at 6 kHz and back to 0 dB at 10 kHz is not gentle.

Notice I am not at all taking issue with what the
station   *sounds*   like.  Why?  Because when I was 
in the position of fabricating a network to produce that 
kind of curve for broadcast transmission that is just
about exactly what I did!  (Mine peaked at 7500.) 
Sounded fine.  The RA-1000 loved it.  

- JimT