Dear Alex, LF Group,
At 13:26 15/10/2002 +0000, you wrote:
So it is very simple to realize! The only addition is input convertion
of the incoming signal
S1(t) = S(t)/[A + S(t)*S(t)]
where S(t) if signal from RX. Parameter A shold be controlled to get
best reciption. Than signal S1(t) is processed by conventional procedure
(say FFT).
It is very interesting to try such an algorithm.
73 de RA9MB/Alex
http://www.qsl.net/ra9mb
As was seen some time ago with the experimental "Hendrixizer" clipping
feature added to Jason, non-linear processing of the signal can certainly
be an improvement under some conditions. The conditions seem to be that the
noise within the receiver passband is wide band in nature; if strong
narrow-band signals are also present, intermodulation and/or blocking
effects occur. Due to the non-linear term in Alex's function above, I
expect the same would apply. But if there is nothing but weak signals and
noise within the RX passband, simply clipping the signal gives a
significant improvement. The effects of clipping were found by accident, so
I would not be surprised if Alex's more scientific approach also gave
benefits - it is certainly true that most of the noise on LF is nothing
like white noise.
Looking at the function Alex suggests, and assuming S(t)*S(t)] means
S(t)^2, when S(t) is small, S1(t) is approximately S(t)/A, ie. linearly
proportional. When S(t) is very large, S1(t) is approximately 1/S(t), ie.
~=0. The gradient "turns over" when S(t)^2 = A. So the function is like a
software noise blanker, removing the high amplitude parts of the input
signal, with the value of A setting the threshold. One can intuitively see
how this could work with LF noise consisting mainly of spikes of QRN
Well, now all I have to do is sit back and relax while the spectrogram
software guys get it working... :-)
Cheers, Jim Moritz
73 de M0BMU
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