On 2/21/2024 8:54 PM, K9MA wrote:
Polarity is just a simple case of 180 degrees out of phase.
Only at a single frequency.
But Phase has meaning only at a single frequency. A network will have a
different phase shift for every frequency.
A length of transmission line will be 180 degrees at only one frequency.
If I want to drive two antennas 180 degrees out of phase for their
entire bandwidth, the only way to do that is to reverse the polarity of
one of them. If I add a half-wavelength to one at the center of their
operating range, they will be 180 degrees out of phase at that
frequency, but +/- some number of degrees as I move away from that
frequency. If they are relatively broadband antennas, that can change
their pattern enough to matter!
73, Jim K9YC
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