That's a good book, isn't it Grant ? :) I have several of the in-house
publications of B&K that are also very instructive.
If its an FIR filter with suitable characteristics, ought to work pretty
well.
Sure would be nice if we knew for sure.
And yes, I agree, the comments are starting to converge on a common idea of
what we think Ten Tec could do with the hardware available.
Gary
----- Original Message -----
From: "Grant Youngman" <nq5t@tx.rr.com>
To: "'Discussion of Ten-Tec Equipment'" <tentec@contesting.com>
Sent: Saturday, December 09, 2006 10:34 AM
Subject: Re: [TenTec] Noise Reduction Setting
> > Allow me to propose a test of the difference between
> > autocorrelation and a narrow filter as the noise reduction
> > process. Check a frequency with multiple weak signals, maybe
> > a multiple tone HF data link. Note that if the NR works it
> > enhances all the signals to noise while a narrow tracking
> > filter would enhance only ONE of those signals.
>
> Actually, not necessarily.
>
> Autocorrelation (and also the cross correlation matrix) IS used in one
form
> or another in establishing the error term between the de-noising filter's
> output and the desired output (the denoised signal).
>
> Most typical adaptive noise reduction algorithms (LMS, leaky LMS, steepest
> descent, LRS, pick one) implement an adaptive Wiener filter. It can be an
> IIR filter, or an FIR filter, but most usually an FIR form filter of some
> number of taps (driven by acceptable processing delays, signal/noise
> characteristics, whatever).
>
> The gain of a Wiener filter at any particular frequency is a function
> (roughly) of the SNR at that frequency (this is a power spectrum ratio,
not
> the usual SNR). So if the SNR is high, the gain fo the filter is high
> (relatively), and if the SNR is low, the gain is low.
>
> As a result, the Frequency Domain characteristic of a Wiener filter
> operating on a signal with multiple spectral peaks (RTTY, SSB, for
example)
> is a filter response that broadly follows the signal spectrum. For
example,
> the Wiener response to a two-tone RTTY signal (depending on adaptions
rates,
> and number of taps in the FIR filter, whether the noise is really Gaussian
> and stationary, all that "etc" stuff) may look more or less like a
2-humped
> thing. The response to a voice signal is going to be something that
> generally has a "bandpass"-like characteristic around the major formants.
> (By the way, this was quite visible in the v1.xx Orion output spectrum).
> You can look at it as "notching" those spectral ranges that contain only
> noise and no signal, or as a bandpass around major signal spectral ranges
> ... Or something. It doesn't really matter since the effect is the same.
>
> I think we're all really on the same wavelength here, but using different
> vocabulary or talking about time-domain vs. frequency-domain, and just
> talking around each other. Of course none of this says anything about the
> actual filter construction in the Orion (or Yaesu or Icom) radios since I
> don't think any of us has had the privilege of seeing the filter
formulation
> or the code or the MATLAB simulation or whatever.
>
> The reference for these comments, in the event anyone cares, is "Adaptive
> Digital Signal Processing and Noise Reduction", Saeed V. Vaseghi, Third
Ed.
> Chapter's 6,7.
>
> Grant/NQ5T
>
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>
>
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