Re: Sensitivity - Was K4 Observations

Posted by Joe Subich, W4TV-4 on May 19, 2019; 2:18pm
URL: http://elecraft.85.s1.nabble.com/K4-Observations-tp7651899p7651916.html

On 2019-05-19 9:50 AM, Wes wrote:
> FT8 reports negative SNRs number but we both know those are bogus.

All of the modes that quote negative SNRs are doing so by using SNR
in a voice (2500 Hz) bandwidth *NOT* SNR in the detector bandwidth
(bandwidth of the final filter whether than be a narrow IF filter,
the "ear-brain" filter or a software [computation] filter).

If one looks at the SNR thresholds of the various Joe Taylor "slow"
modes, 80% of the "negative" SNR can be attributed entirely to the
difference between the occupied bandwidth and the [excess] measurement
bandwidth.  The remainder can be attributed to software processing
algorithms that take advantage of the fact that noise is random while
the signal is not - in essence reporting using a "peak noise" level
while actually decoding against a "minimum noise" level (like copying
CW through static crashes - one looses a dit/dah during the crash but
fills that in from the context).

73,

    ... Joe, W4TV


On 2019-05-19 9:50 AM, Wes wrote:

> I feel like I'm gonna be slappin' a tar baby by responding.
>
> Since we are discussion HF radios, I was assuming HF.  I realize
> JT65(-HF) and JT9 have been used on HF, but the QSOs are hardly random.
> If your computer clock is off, sorry, no QSO.  FT8 reports negative SNRs
> number but we both know those are bogus.
>
> Wes  N7WS
>
>
> On 5/19/2019 5:58 AM, Ed W0YK wrote:
>> JT65, JT9, FT8.
>>
>> 73,
>> Ed W0YK
>>
>> -------- Original message --------
>> From: Wes <[hidden email]>
>> Date: 5/19/19 07:49 (GMT-06:00)
>> To: [hidden email]
>> Subject: Re: [Elecraft] Sensitivity - Was K4 Observations
>>
>> What current modes hear below the noise level?
>>
>> Wes  N7WS
>
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