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Resonant vs Non-Resonant Antennas

Discussion in 'CB Antennas' started by Hamin' X, Aug 21, 2006.

  1. Hamin' X

    Hamin' X Active Member

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    Here is an excellent article on the subject.

    Antennas and Feedlines by W6WQC

    He puts it into much better words than I can. It's rather long, but well worth the read.



    Rich
     
  2. freecell

    freecell BANNED

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    <snip>

    "from all of this we see that there are TWO TYPES OF RESONANT WIRES: A wire that is PHYSICALLY a half wave long (or any number of 1/4 waves) and a wire that is a random (non-resonant) length but whose reactance component has been canceled or tuned out. Thus RESONANCE can be achieved by either of two means: physically pruning the wire (length) or ELECTRONICALLY TUNING IT. Whichever method is used, maximum current flows in both wires compared to the current that flows before the wire was pruned or the reactance tuned out."

    <snip>

    maximum current flows when X = 0.

    even the author of this article makes a small contribution to the confusion with careless comments like this:

    "This clearly says that an antenna is resonant when the reactance is eliminated. This is exactly what a tuner does when used with a random length wire. When the reactance is canceled, whether by pruning the wire or by the use of a tuner, (matching network, transmatch) the antenna is made resonant and current is maximized compared to the current that flows before the reactance is eliminated."

    some readers may equate his use of the word "eliminated" as there being no inductive or capacitive reactance present at all and this is not the case. in the third sentence he uses the word reactance again referring to it as *cancelled. this is correct as it describes exactly the quantities of each of the two different types of reactance. when *used as an intransitive verb: cancel, to neutralize one another; counterbalance: two opposing forces that cancelled out.

    Reactance (symbol X) is a measure of the opposition of capacitance and inductance ... The total reactance (X) is the difference between the two: X = XL - Xc ... it's clear to see that the only time that X = 0 is when values for both Xl and Xc are identical.

    even Maxwell concurs here as he recommends the use of line matching at the transmitter input to achieve basically the same results, only in this case the feedline and the antenna are adjusted for resonance as a single unit. again, "the purpose of resonating either the antenna or the system as a whole is simply to allow power to be fed to the antenna easily."

    otherwise an excellent article.
     

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