On Fri, 2006-03-17 at 14:30 -0600, Grant Youngman wrote:
> > I'd prefer it the way it was done for almost a century, and
> > it worked that way in V1, so it's clearly a degradation.
>
> I'd offer the following recent paper by Dallas Lankford as interesting
> reading. While it addresses specifically AM distortion caused by fading,
> there are some other useful points. If you're not into formulae, scan for
> the conclusions peppered throughout the document.
>
> One of those, in particular, is that (approximated to the 2nd harmonic),
> distortion in a square law detector is actually lower when a steady state AM
> signal is tuned to remove most of one sideband than when the carrier is
> centered in the passband. Centered, the percent harmonic distorion is
> approximately 6.25*m**2 and shifted to remove most of one sideband it is
> approximately 1.5625*m**2, where m is the modulation index.
>
> This doesn't exactly "rest the case" because measured results were somewhat
> different (for reasons the author may still be investigating), but the paper
> does rightly point out that there are more serious forms of distortion to
> worry about than that which might be caused in a real radio from shifting
> the passband. The benefits of "offset tuning" an AM signal to reduce fading
> distortion is pretty well known to serious SWLers.
>
> Maybe it's something worth measuring.
>
> The paper can be found here -- http://tinyurl.com/fxp6a
>
> Grant/NQ5T
>
>
When the detector is seeing a volt or two of signal, its way above the
square law region.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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