On Wed, Jun 10, 2020 at 08:58 AM, <gary.sewell@...> wrote:
My question is: what are the other points that look like
resonance,
Appearances can be deceiving. Those are points at which the phase _display_ is wrapping around from 180 degrees to -180 degrees or vice versa - think of them as anti-resonant points. The phase never actually approaches 0 degrees (resonance) at those frequencies.
and should I trim my antenna based on phase? If so which one?
Trimming based on minimum SWR in the center of the band should work well. Or, you can trim at the point of 0-degree phase crossover (the actual crossover in the center of your graph, not the two illusory ones on the left and right). These two frequencies (minimum SWR and zero-phase) will usually be quite close to one, if you're dealing with an antenna which is designed to offer a near-50-ohm impedance, so it won't matter too much which one you use.
Other people say "trim so that you have an acceptably-low SWR across the frequency range you are interested in" and don't worry as much about where the actual minimum falls.
