At 15:07 2004-02-25 -0800, you wrote:
>
>--- Walter Knapp <> wrote:
>> From: "Rich Peet" <>
>> >
>> > The things that I am fighting myself with here are:
>> > 1. Is it agreed that the size of the focal globe changes with
>> > frequency?
>>
>> I'm not so sure but what the focal globe idea is not misleading or at
>>
>> least misused. In my visualization of things, if it exists as a
>> useful
>> concept, then it's size is not frequency dependent. It's dependent
>> primarily on how well the dish conforms to a ideal parabola, and how
>> far
>> off axis we are including in the 'globe'.
>
>I may be wrong, but I think the size of the globe must be frequency
>dependent. I believe this is true especially if you have an ideal
>parabolic reflector.
>
>As you move a given distance from the absolute point of focus, this
>distance is a larger phase difference for shorter wavelengths than it
>is for longer wavelengths. This phase difference at the off focus
>position is one mechanism that would give rise to interference or
>cancelation rather than the addition of pressure as occurs at the
>absolute focus (because the arrival at focus is in phase from all dish
>reflecting points).
>bret
>
It also go along with practical experiments which I have made.
Klas.
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
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