Posted by
Evert Bakker (PA2KW) on
May 19, 2019; 3:34pm
URL: http://elecraft.85.s1.nabble.com/K4-Observations-tp7651899p7651921.html
We all now (i guess) that decoding below the noise floor needs:
Time, timing and repetition..
no formulas needed .....
73's, Evert PA2KW
-----Oorspronkelijk bericht-----
Van:
[hidden email] [mailto:
[hidden email]] Namens Joe Subich, W4TV
Verzonden: zondag 19 mei 2019 15:29
Aan:
[hidden email]
Onderwerp: Re: [Elecraft] Sensitivity - Was K4 Observations
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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