[TenTec] 2.033

[Douglas Shock]

right on Gary...thanks for the insight!

On 5/3/06, Gary Hoffman <ghoffman at spacetech.com> wrote:
>
> I just meant that 15 kHz is a frequency in the audio range.  I know it is
> used as an IF frequency in the Orion.  The point was that the frequency is
> very low....low enough that DSP chips can process the data in the manner I
> indicated.
>
> I was talking about DSP Noise Reduction.  Bandwidth filters are another,
> simpler, thing.
>
> Gary
>
>
> ----- Original Message -----
> From: "Douglas Shock" <douglas.shock at gmail.com>
> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
> Sent: Wednesday, May 03, 2006 3:08 PM
> Subject: Re: [TenTec] 2.033
>
>
> > Gary,
> > you sure the dsp BW filtering is audio? Seems to me that it is in the
> 3rd
> if
> > at 14KhZ? Is my thinking wrong? Now if you are talking about NR then I
> agree
> > with you.
> >
> > And I agree with your expected DSP explanation...this is what I am
> > accustomed to.
> >
> > On 5/3/06, Gary Hoffman <ghoffman at spacetech.com> wrote:
> > >
> > > FWIW.....not ALL DSP just narrows bandwidth.
> > >
> > > The way it worked when I used to work with audio DSP systems in a
> previous
> > > life (and the IF of the Orion is at an audio frequency) is that each
> > > sample
> > > of the A to D converter is compared to those around it, and a
> correlation
> > > level is established.  (Excuse me that I've forgotten the correct
> > > technical
> > > language they used).  Speech and tones (like CW) are highly
> correlated,
> in
> > > that each sample tends to be relatively closely related to those that
> came
> > > before.  Random noise, of course, is not highly correlated.
> > >
> > > The noise is reduced by simply deleting those samples not correlated.
> > >
> > > Then the remainder go through D to A and come out as sound again.
> > >
> > > The NR reduction level control (or whatever its called) simply shifts
> how
> > > much correlation is required before a sample is either kept or
> > > rejected.  A
> > > higher setting requires more correlation before the sample is
> kept.  Of
> > > course if you turn it up too high, then too many samples are rejected,
> and
> > > you get weird sounding sound after you go back from Digital to Audio.
> > >
> > > Has nothing whatsoever to do with a bandwidth limiting filter.  That,
> of
> > > course, is another approach, which works to a certain degree
> also.  But
> > > not
> > > what a real DSP noise reducer does.
> > >
> > > Now....how much of each does the Orion do ?  That I cannot tell you,
> not
> > > being privvy to the design details.  Perhaps the folks at Ten Tec
> would
> > > like
> > > to tell us ?
> > >
> > > Note - years ago, when I did this, we could do it on the fly with a
> DSP
> > > processor.  I'm sure the processors they have now far outperform the
> ones
> > > we
> > > had then.  So, its doable, and practical, essentially with a single
> chip.
> > >
> > > 73 de Gary, AA2IZ
> > >
> > >
> > > ----- Original Message -----
> > > From: "Bill Tippett" <btippett at alum.mit.edu>
> > > To: <tentec at contesting.com>
> > > Sent: Wednesday, May 03, 2006 7:05 AM
> > > Subject: Re: [TenTec] 2.033
> > >
> > >
> > > > NQ5T:
> > > >
> > > >  >the one thing I'm absolutely certain of is that it
> > > > adds nothing to (S+N)/N ratio, and at any BW below
> > > > about 1000 Hz actually degrades it.
> > > >
> > > >          Just to clarify Orion's implementation
> > > > of DSP NR, I believe your statement is true for ANY
> > > > DSP rig with real-time processing (i.e the DSP is
> > > > achieving NR simply by BW reduction).  To do more
> > > > (e.g. JPL's image enhancements) requires reprocessing
> > > > the recorded signal many times with literally hours of
> > > > latency even using super-computers.
> > > >
> > > >          There is no free lunch and DSP is not magic,
> > > > despite what some manufacturers (notably not Ten-Tec)
> > > > would lead you to believe.
> > > >
> > > >                                  73,  Bill  W4ZV
> > > >
> > > > _______________________________________________
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> > > >
> > >
> > >
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