I've often wondered what the effective bandwidth of a good CW operator
was. I've noticed that, unless there's QRM, reducing the receiver
bandwidth really doesn't help, so the limit factor is the "processing".
On the other hand, neither does slowing down below perhaps 15 wpm, as if
the processing just can't make the effective bandwidth any lower.
Perhaps the real advantage of the JT modes is that they can take
advantage of the lower noise bandwidth at very slow speeds, while our
brains can't. It would be interesting to compare the performance at 15 wpm.
73,
Scott K9MA
On 5/19/2019 09:18, Joe Subich, W4TV wrote:
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 <[email protected]>
Date: 5/19/19 07:49 (GMT-06:00)
To: [email protected]
Subject: Re: [Elecraft] Sensitivity - Was K4 Observations
What current modes hear below the noise level?
Wes N7WS
--
Scott K9MA
[email protected]
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