Hi Joe,
On 12/9/2023 9:56 PM, w0fy--- via wsjt-devel wrote:
Been wondering how WSJT-X generates the noise power estimate it uses to
calculate SNR for each FT8 signal. Does it simply collect all the
signals and noise over the bandwidth selected on the waterfall and call
that the noise power level or does it take a quick snapshot of the
background noise level during the brief quiet period at the end of each
15 second FT8 sequence? Or is it more complicated than that?
This question has been asked and answered many times on this and similar
forums. WSJT-X measures noise power by computing the spectrum of the
receiver's output, averaged over the reception interval, and fitting a
baseline to the regions that have no discernible signal present. The
resulting value -- effectively a noise power density, or power per unit
bandwidth -- is then scaled to yield noise power in 2500 Hz bandwidth.
I am plagued with a S2 -S3 noise level on 6 meters nearly all the time
that if not AWGN is pretty close to it. 10 meters is even worse. The
DSP noise blanker in my TS590 will reduce it slightly. I estimate this
is degrading my ability to decode FT8 signals on 6 by nearly 20 dB
compared to the noise level generated by a 50 ohm resistor. I don’t use
an LNA ahead of the radio – would be pointless. I don’t use the noise
reduction feature in the radio either as it tends to lose very weak
signals completely.
It's OK to use your receiver's noise blanker to remove impulsive noise.
Do NOT use "noise reduction" features, and do NOT use a receiver
bandwidth narrower than about 2.5 kHz. Wider bandwidths are even
better, up to 4 or 5 kHz. WSJT-X does all necessary narrow-band
filtering in software.
-- 73, Joe, K1JT
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