J-Pole antennas for
2m-40m with
Wireman-cable
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The picture shows
the scheme of a J-Pole antenna. The high impedance feeding point of a l/2-wire
(L1) is matched from some KOhms to a low impedance with a
l/4
matching sector (L2). The point XX has an impedance of 50Ohm
for direct feed with a coax cable. XX is symmetrical, a choke or
balun could be useful to avoid sleeve waves on the screen of the coax. A
very simple method for the l/4-part
is to use a 450-Ohm-Wireman cable. I have built up
the antenna for 2m, 6m, 12m and 30m. The table gives the values for
experimenting with the other bands.
L1=0,471l
(Halfwave-Radiator) L2=0,223l (Wireman-cable)
Solder
the braid of the 50-Ohm-coax at the left X, the inner conductor to the right X.
XX about 5-10% of L2.
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The antenna can be mounted in several ways:
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The classic J-Pole with both sections mounted vertically.
Length 3/4-l,
only for the higher bands.
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It is no difference in the radiating conditions, if the l/4-part
is vertical or horizontal. The pattern is identical with a
vertical dipole. |
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Both parts horizontally mounted |
The "Zepp"-configuration |
The antennas were tested on 2m, 6m, 12m and 30m. The lengths for the bands
marked with "*" have not been tested, try with he given dimensions.
For other frequencies use the following fomulas for insulated 2mm-wires for L2.
Not-insulated wires need a longer L2-section.
L1=0,471l
(Halfwave-Radiator) L2=0,223l (Wireman-cable)
The
points X-X are 5-10% from the shorted part of the Wireman-cable (look for best
SWR).
For
the 50MHz-J-Pole look on the special page: 50MHz-Halfwave-Verticals
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Band
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l/2-
Wire
(insulated)
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l/4-
Wireman
V=0,905
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XX
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Fo
MHz
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SWR
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Bandwidth
SWR<1,5
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40m*
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20,02m
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9,46m
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73,0cm
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7,05
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-
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100KHz
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30m
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13,96m
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6,61m
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58,5cm
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10,12
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1,1
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150KHz
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20m*
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9,98m
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4,73m
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35,0cm
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14,15
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-
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200KHz
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17m*
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7,80m
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3,70m
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26,5cm
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18,1
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-
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250KHz
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15m*
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6,66m
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3,15m
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22,5cm
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21,2
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-
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300KHz
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12m
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5,67m
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2,67m
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18,5cm
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24,91
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1,0
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350KHz
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10m*
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4,96m
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2,45m
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15,5cm
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28,5
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-
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500KHz
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6m
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2,815m
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1,33m
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6,5cm
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50,15
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1,1
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1000KHz
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2m
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0,975m
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0,47cm
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3,5cm
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145,2
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1,0
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1500KHz
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The result of 10 Minutes work with the 12m-J-Pole, mounted on
a fishing rod:
