Are primes brighter and sharper than wide open zooms
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October 5th 05, 05:05 AM
external usenet poster
(DoN. Nichols) wrote:
According to Floyd Davidson :
Here is the technical definition of "continious wave", according
to the FTC 1037C Standards, available at
continuous wave (cw): A wave of constant amplitude and
Clearly it means a transmission that is neither amplitude,
frequency, nor phase modulated. Any such modulation necessarily
must cause a discontinuity in the wave. The only thing you can
do is turn it on and off... which is called radio telegraphy!
Well ... to *my* mind, even keying (turning on and off) is a
form of amplitude modulation -- a rather extreme one at 100% modulation.
Except that it is *not*.
And it is certainly causing a discontinuity in the wave.
If the wave is *not there*, it just doesn't exist and has no
characteristics. When it is there, it is not being modulated.
Turning it on and off may well produce some modulation effects,
but that "modulation" is not being used to pass information, and
in fact is a form of distortion that actually interferes with
the information rather than enabling it.
Of course when we get down to practical implementations, in
almost all cases we do have to treat c.w. as if it a modulation,
mostly in order to "shape" the distortion products in ways to
reduce the effects.
While the difference may not be obvious even at typical
c.w. speeds, and might be very hard to see at higher speeds...
think about such things as the very slow speeds often used for
such things as the original moon bounce work, or for breaking
path distance records at microwave frequencies. Circumstances
where a "dash" might be 10 or 20 seconds in length.
Ukpeagvik (Barrow, Alaska)