[Elecraft] K3: LPF, bass audio, new DSP board: Stirring the pot?

[Jim Brown]

On Mon, 28 Dec 2009 20:33:03 -0800, Fred Atchley wrote:

> Human hearing in the 20 kHz range is not unheard of. 

We start out that way as children, but suffer hearing loss from 
multiple sources, mostly due to exposure to excessively loud 
sounds. 

>I wonder if the K3 design cuts this off above 5 kHz or if 
>it allows it to pass through the audio stage?

Good engineering practice would include high pass and low pass 
filters at the limits of transmitted bandwidth. For ham 
circuits, 300 Hz and 3.5 kHz would be good cutoff frequencies 
for 3-pole filters for HF radios. For AM broadcast, 40 Hz and 9 
kHz (US) and 8 kHz (EU) are about right. It should also be noted 
that roughly two decades ago, AM broadcasting adopted the 
practice of HF pre-emphasis like with FM and analog TV. But 
PULEEZE don't tell the wideband AM lunatic fringe. 

As Riley Hollingsworth said so eloquently when he was running 
the FCC's Enforcement Bureau, if you want to be a broadcaster, 
buy a broadcast license or get a job at a radio station. 

So yes, there ought to be user-definable high pass and low pass 
filters in the audio system. There ARE such filters in the IF, 
but not in the audio system. The result is that if gains are not 
well managed in the K3, some of our younger users could hear 
hiss. Since my highs are long gone, I can't comment on that. :) 

73,

Jim K9YC