How
can I make a Dipole Antenna?
Antenna Construction
The Dipole Antenna is a 72 ohm
(approximately) bi-directional antenna and is made by attaching (i.e. soldering
or other secure electrical connection) two (2) wires, equal in length, to
the feed line as shown below:
Length of Dipole Wire Antenna (B
Length)
The physical length of a resonant dipole antenna is shorter
than a half wavelength in free space. Therefore, the physical length of a
dipole must be made approximately 5% shorter than that value calculated from
the free-space wavelength equation. A half wavelength antenna in free-space
has the following length:
λ (1/2 wavelength antenna in
Feet) = 492 / Frequency (Mhz)
A half wavelength (Length B) antenna with 5% reduction in
length has the following length:
λ (1/2 wavelength antenna in
Feet) = 468 / Frequency (Mhz)
Example:
Calculation for a 20 meter or
14.200 Mhz (14,200,000 hertz) antenna is as follows:
λ (1/2 wavelength antenna in
Feet) = 468 / Frequency (Mhz)
λ (1/2 wavelength antenna in
Feet) = 468 / 14.2
λ (1/2 wavelength antenna in
Feet) = 32.96' or 32' 11.5" (.96 x 12")
So if B = 32.96', then A=
32.96' x 0.5 or 16.48'
Pre-Calculated
Dipole Wire Antenna Lengths
Here are pre-calculated lengths for fabricating a half wave
dipole antenna. Take the B Wire Length dimension and cut it in half creating
two equal half lengths known as A.
|
Band in Meters |
CW Band |
SSB Band |
|
B Wire Length |
Frequency (MHz) |
B Wire Length |
Frequency (MHz) |
|
160 |
256' 5" |
1.832 |
256' 5" |
1.832 |
|
75/80 |
128' 3" |
3.510 |
120' 0" |
3.800 |
|
40 |
65' 11" |
7.025 |
64' 7" |
7.200 |
|
20 |
33' 2" |
14.025 |
32' 9" |
14.200 |
|
15 |
22' 1" |
21.025 |
21' 11" |
21.300 |
|
10 |
16' 7" |
28.025 |
16' 1" |
28.450 |
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Installing a Dipole Antenna
The Dipole Antenna is a bi-directional antenna. This means
you can receive or transmit a signal much stronger in two directions (both
sides) and weaker off both ends as shown below. Therefore, you need to make
sure the sides of the antenna are in the direction you want to
receive/transmit the loudest.
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