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Old January 15th 04, 04:17 PM
Richard Harrison
 
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Roger wrote:
"Any special considerations?"

A dipole in the HF range using aluminum strip 10 inches wide and .006
inches thick has a small length to width ratio and that`s good for
bandwidth. The width is sufficient for good surface conduction and that
is good for efficiency.

Most data are for copper but aluminum is only 1.6X as resistive as
copper, so there is not much electrical difference in performance. .006
inch is sufficiently thick to prevent significant RF penetrationat at
HF, and if RF did penetrate it would not be detrimental.

Bandwidth of an antenna may be determined by acceptable directional
character or it may be determined by acceptable drivepoint impedance.

Ed Laport in "Radio Antenna Engineering" has made a "Free-Space Dipole
Characteristics" table for bandwidth as limited to the region where the
antenna`s reactance is less than its radiation resistance at resonance.

At 10 MHz, a dipole made of Roger`s aluminum strip would have an
equivalent length over diameter (L/D) of about 59.

From Laport`s Fig. 3.1 on page 248, a dipole of L/D of 200 would be
resonant at an electrical length of 168.3-degrees. Its 3 dB bandwidth is
11.2% and its 1 dB bandwidth is 5.6%. The aluminum strip dipole at 10
MHz has a smaller effective L/D and produces a wider bandwidth than any
shown in Laport`s table.

Consult "Radio Antenna Engineering" for more information.

Best regards, Richard Harrison, KB5WZI

 
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