[Elecraft] Filter Recommendations

[Jim Brown]

On 8/27/2018 10:01 AM, Bob McGraw K4TAX wrote:
> Per one authority on receiver performance, the optimum receiver 
> performance occurs when the no signal band noise is about 10 dB above 
> the receiver noise floor.

Not quite -- when the noise from the antenna is 10 dB above the receiver 
noise, the combined noise is fractional dB greater than the antenna 
noise alone. As the ratio increases (13 dB from the antenna, for 
example), that fractional dB becomes even smaller.

A common misunderstanding is that 1 dB is the smallest change in 
loudness that average listeners can hear, but the ear is FAR more 
sensitive to differences between signal and noise at low signal to noise 
ratios, so fractional dB improvements can make the difference between no 
copy and just enough to get the rare DX in the log. :)

Another manifestation of this is mixing multiple mics that pick up the 
various parts of a band or orchestra. Anyone who's done much live mixing 
will tell you that when the balance relative to the rest of the band of 
a vocal or instrument is not quite right, the volume slider for the mic 
in question rarely needs to move more than a dB or two. In other words, 
the ear-brain is far more sensitive to differences between sounds than 
to absolute loudness of the combination of the sounds it hears.

73, Jim K9YC