Re: Sensitivity - Was K4 Observations

Posted by Joe Subich, W4TV-4 on May 19, 2019; 1:28pm
URL: http://elecraft.85.s1.nabble.com/K4-Observations-tp7651899p7651912.html


Buck,

New mode "hear below the noise" in a normal SSB bandwidth even
though they may be as narrow as 16 to 50 Hz (in the case of
JT9 and FT8).

The largest part of the claimed -21 to -27 dB S/N threshold is
based on the difference in noise bandwidth.  The actual "filters"
for each of the "tones" are just 1 - 2  Hz wide and there one
still needs to "hear atmospheric noise."

Using the standard 10*log(BWn/BWw) equation, one needs to hear
~20-25 dB atmospheric noise (4-5 S units in a K3/K3S) before
reducing the RF gain! This is, however, not really any different
than switching from SSB to CW ... if the "effective" bandwidth
for CW is on the order of 100 Hz a CW signal right at the noise
in the 100 Hz "ear/brain filter" would be -14 dB in a 2500 Hz
wide SSB filter.

73,

    ... Joe, W4TV


On 2019-05-19 7:42 AM, Buck wrote:

> Here's a question about sensitivity.  We used to say if you could hear
> the atmospheric noise, that was enough.  Time to reduce RF gain.
>
> New modes hear below the noise and DSP is getting better at removing it.
>   Does that mean our "old" wisdom is now wrong and sensitivity below the
> noise level is useful?
>
> Buck, k4ia
> Honor Roll
> 8BDXCC
> EasyWayHamBooks.com
>

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