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

[Kevin Tekel]

Bob Orban wrote:
> This comment misses the point. If the transmission includes energy 
> between 7 and 10 kHz, it takes up extra "room" in the modulation 
> envelope. Getting a 0 - 10 kHz bandwidth transmission to sound as 
> loud as a 0 - 7 kHz transmission on an average radio requires the 
> audio to be clipped and limited harder, regardless of the details of 
> how it is done in the audio processor.

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.

Even with only 1 kW, their loudness and clarity on the dial matches or
even exceeds that of any of the 50 kW NYC signals, including those which
are brickwalled at 8, 6, or 5 kHz.  They manage to be just as loud as WOR,
without sounding over-processed, even on MC13020-based C-Quam receivers,
which are typically intolerant of stations which push the negative
modulation too close to -100%.

And by allowing the highs to smoothly roll off, they sound much more
pleasant on a wideband receiver, compared to the harshness and "ringing"
of stations which sharply brickwall the audio right at the height of their
pre-emphasis boost.  (It takes the narrowest of narrowband receivers to
make a 5 kHz signal sound acceptable, which WCTC sounds good on any
receiver, from the dreadfully narrowband factory radio in my 2007 car, to
my Denon TU-680NAB and GE Superadio III in "wide" mode.)




       
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