> Why don't hams place the LP filter between the Xcvr and
Probably because it won't help reduce TVI. It's virtually
always a waste of a filter.
> way, the amount of harmonics reaching the Amp will be
> rendering their output levels relatively the same, if not
lower, than if
> the LP filter was AFTER the Amp.
The amp won't amplify harmonics anyway if it is properly
We have to remember what causes harmonics. Harmonics are
caused by fractional cycle non-linearity or distortion, NOT
by gain compression or envelope non-linearity. The effect
causing splatter is entirely different than the effect
The waveshape over every RF cycle before filtering causes
harmonics. Most PA's conduuct over a fraction of the RF
cycle, and have a large portion of each RF cycle where the
slope of the sine wave is changed to something other than a
perfect sine wave. Many PA's actually only have just over
180 degrees of linear conduction in each RF cycle, so they
generate strong harmonics.
The very same PA can have a very good transfer function.
Output power can track input power closely, so the Pa will
have good envelope linearity and low splatter or IM
If a low-pass between the exciter and PA helps things, it
means the exciter or PA is poorly shielded or very poorly
designed or constructed.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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