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Is it true that for a half wave dipole, cancelling out reactance using for example a gamma match does not make the antenna resonant at all, but rather just cancels out the reactance of what is actually a non-resonant antenna which has an impedance when fed from the center of 73 + j43 ohms ?

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An strictly half-wave dipole isn't resonant. As you say, it has an impedance around 73+j43 ohms. Since the reactance is non-zero, it is by definition not resonant.

Any manner of matching devices could be added to the antenna, and considered as a whole, they would make a resonant system. But that's not what people usually mean when they say "resonant antenna".

Instead, the antenna can be made just a little shorter. At slightly less than a half-wavelength the reactance drops to zero and the antenna becomes resonant, no matching device required.

In practice this is almost always done, so unless writing in a context where very strict language is required, a "half-wave dipole" really means "a dipole of approximately a half-wave, adjusted to achieve resonance."

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  • $\begingroup$ thanks now i understand that part, any chance of answering the other questions in this question ? $\endgroup$ – Andrew Dec 10 '19 at 5:44
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    $\begingroup$ Maybe try asking fewer, more coherent questions now that the misconception has been cleared up? $\endgroup$ – Phil Frost - W8II Dec 10 '19 at 5:46
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    $\begingroup$ RE: Instead, the antenna can be made just a little shorter. At slightly less than a half-wavelength the reactance drops to zero and the antenna becomes resonant, no matching device required. — However that shorter radiating length also has less radiation resistance. According to John Kraus in ANTENNAS... (3rd Ed), it drops to about 65 Ω, which, without a matching device would produce an SWR of about 1.15:1 to a 75 Ω transmission line connected across its feedpoint terminals., $\endgroup$ – Richard Fry Dec 10 '19 at 12:13
  • $\begingroup$ @RichardFry Are you saying an SWR of 1.15 requires a matching device? In any amateur application, I think not... $\endgroup$ – Phil Frost - W8II Dec 10 '19 at 21:10

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