[TenTec] Noise Reduction Setting

[Gary Hoffman]

Yes, what was explained at the bottom is about right.

We did not have to have adaptive filters in the applications I used, because
the signal environment was always somewhat a given.  But you could adapt at
least a little by using some simple switching.


----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at storm.weather.net>
To: <tentec at contesting.com>
Sent: Friday, December 08, 2006 2:43 AM
Subject: Re: [TenTec] Noise Reduction Setting


> On Thu, 2006-12-07 at 20:24 -1000, Ken Brown wrote:
> > It's news to me that SAWs are processors. I would be more inclined to
> > believe that a SAW filter may be used in front of some type of dsp
> > processor.
> >
> > Last time I read about Surface Acoustic Wave devices they were basically
> > bandpass filters, that work similarly to Collins mechanical filters. The
> > electrical signal is converted into a mechanical signal using some type
> > of electromechanical transducer (like a piezoelectric device, or a
moving
> > coil device) and then propagated through some mechanically resonant
> > parts, later to be converted back to an electrical signal by another
> > electromechanical transducer. In the case of Collins mechanical filters
> > the signal travels as torsion in a rod, which has resonant disks
> > attached. In a SAW the signal travels as, you guessed it, a surface
> > acoustic wave, and the surface it travels across has some resonant
> > pieces either etched out or deposited upon it.
> >
> > I've probably got some of the details, or maybe even the whole concept,
> > wrong. I'd love to hear about it from someone who has a better, more
> > authoritative explanation of either mechanical filters or SAWs. Is a SAW
> > a processor? Or is it just another way to make a bandpass filter?
> >
> > DE N6KB
> > >  In the military applications for example, SAW processors (Surface
> > > Acoustic Wave) handle this nicely, as do various hard wired ASICS.
The
> > > latter are comparatively cheap.  Neither do much actual processing, as
the
> > > algorithm is pretty much hard wired in.
> > >
> > >
> SAW devices can do the autocorrelation process. Might be two input
> transducers, at different distances from the output transducer. The
> distance chosen to put a preferred frequency in phase, but noise out of
> phase. So it accomplishes the correlation function of adding the signal
> and a time delayed signal so that the repetitive signal adds, but the
> random noise doesn't add. Just its not adjustable for delay, and picking
> that delay is how the DSP adjusts the process to adapt.
> -- 
> 73, Jerry, K0CQ,
> All content copyright Dr. Gerald N. Johnson, electrical engineer
>
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