Re: Resonant Antenna


From: Bill Coleman (
Date: Wed Aug 22 2001 - 16:13:04 CDT

On 8/12/01 2:35 PM, Mike Branca at wrote:

>Also unless we are putting power into a resistor any antenna must be

A resistor is perfectly resonant at a large range of freuencies.

But, no, the ANTENNA need not be resonant. The Antenna SYSTEM often is,
because we typically use a tuner.

> The above described 100 foot antenna is resonant on 80 thru 10

The antenna isn't resonant, the antenna SYSTEM defined by the antenna,
feedline and the tuner IS. (Or is when the tuner is properly adjusted.

> One must understand that we are talking about an antenna system
>composed of the radiating element (100 foot of wire), the open wire feed
>line and the antenna tuner. The tuner simply supplies the missing L and C
>values that the feed line and antenna need to achieve resonance.

Specifically, to acheive a conjugate match -- which results in a resonant
condition (defined as an impedance Z with no imaginary component).

>compared to a dipole this shortened antenna is only slightly less efficient
>on 80 meters and comparable, in energy radiated, on the higher bands.
>The danger in such resonant Vs non resonant antenna discussion is for the
>new hams who are presented with the idea that somehow there is radiation
>magic in a specific length of antenna. Filling the discussion with a lot of
>math further confuses the subject. Its like asking which is bigger 12 or a

The key to maximizing antenna radiation is minimizing loss. Energy that
is not lost to heat MUST be radiated as a signal.

Some people confuse resonance with a low-loss condition. This is partly
true, particularly with coax-fed antennas, since complex impedances on
the coax lead to a lot more loss in the system.

But resonance is not a guarantee of low-loss. A dummy load is perfectly
resonant, but also perfectly lossy.

Bill Coleman, AA4LR, PP-ASEL Mail:
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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