On Fri, 22 Jan 2010 20:16:59 -0800, jimlux wrote:
>If you have a time delay between the two antennas (as opposed to a phase
>shift), then the time delay sets the angle, frequency independent. Since
>most folks use a hunk o' coax for the phasing, then you're good to go.
Actually, the coax provides a TIME offset, NOT phase shift. There is a
resulting phase shift from a TIME offset, that is proportional to
frequency.
>If you're using phase reversing (e.g. in phase, out of phase) then it
>doesn't work as well.
When you reverse the wires in a system, you are not changing PHASE, you
are changing the POLARITY. When you reverse the polarity, there is NO
change in time (or delay) or phase, but you invert the waveform, and the
signal is complex (fundamental plus harmonics, or carrier with
sidebands), the signal is inverted at ALL FREQUENCIES.
Phase is a continuously valued function, and is related to delay by
angular frequency. If you add DELAY (with coax, for example) the phase
shift is proportional to frequency. For example, if the phase of the
fundamental is shifted by 45 degrees, the second harmonic will be shifted
by 90 degrees, the third harmonic by 135 degrees, and so on.
BTW -- the guy who hammered at the pro audio world to make us understand
and clarify our concepts of polarity, time, and phase, was the late Dick
Heyser, who worked at JPL in space communications. When he died, he was
chair of the AES Standards Committee Working Group on Polarity and
President Elect of the AES.
Why is this important? In the simplest example, causing two antennas to
be out of polarity (by reversing their feeds) makes them cancel at ALL
frequencies, not only one (assuming they are identical). Think about
this in the context of a broadband signal! Everything we deal with in
audio is a broadband signal, which is part of why Dick hammered us about
understanding these fundamental concepts.
73,
Jim Brown K9YC
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