[hpsdr] "Taylor Corrected DDS"

[John B. Stephensen]

Yes, but its much better than the uncorrected output of a sine lookup ROM
and good enough for making small frequency adjustments when digitizing a
band-limited IF. Given that I'm getting more efficient at utilizing FPGA
resources and have extra block RAM now, I'll have to try what you describe.

73,

John
KD6OZH

----- Original Message ----- 
From: "Robert McGwier" <rwmcgwier at comcast.net>
To: "John B. Stephensen" <kd6ozh at comcast.net>
Cc: "Bob McGwier" <n4hy at idaccr.org>; <hpsdr at hpsdr.org>
Sent: Thursday, June 15, 2006 00:52 UTC
Subject: Re: [hpsdr] "Taylor Corrected DDS"


> John:
>
> Your way will be faster,  smaller, and will have much poorer
> performance.    The 2^12 * 2^8  will be "secants"  connecting the 2^20
> points on the circle as defined by the trig identities and the two
> tables.  The 2^12 linear interpolation will simple yield secants between
> the 2^12 points in the first table.   The 2^12 * 2^8 will be an exact
> match to the correct complex numbers on all 2^20 points.  The linear
> interpolation way will NEVER be on the correct value between the 2^12
> original points.   This will have significantly higher total harmonic
> distortion, spurs, etc.
>
> 73's
> Bob
> N4HY
>
>
>
> John B. Stephensen wrote:
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> > A simpler and smaller mechanism is to do linear interpolation between
the
> > points in a sine table.
> >
> > 73,
> >
> > John
> > KD6OZH
> >
> > ----- Original Message ----- 
> > From: "Bob McGwier" <n4hy at idaccr.org>
> > To: <hpsdr at hpsdr.org>
> > Sent: Wednesday, June 14, 2006 18:04 UTC
> > Subject: [hpsdr] "Taylor Corrected DDS"
> >
> >
> >
>
> -- 
> AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
> NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
> Laziness is the number one inspiration for ingenuity.  Guilty as charged!
>


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