Production and test of double line J pole antennas, J-Pole Antenna
Keywords: double line J pole antenna production and testing
Double line J pole antenna production and test
The J-pole (J-POLLE) antenna is composed of a 1/2 wave transmit element (part A) and a 1/4 wave driver match (part B), which is equivalent to an even from the end drive The extreme antenna, because its conductor is a J, so it is called J poles. The picture is a J pole antenna (suitable for 30W or less, referred to as two-line J pole antenna) with 300 ohm television antenna flat line.
The two-line J pole antenna is easy to make, easy to carry, easy to hide. The following detailed description of its production steps:
Calculate the vacuum wavelength: l = 300 / fm, where F is the transmit frequency (MHz)
Calculate the lengths A, B, C: A = 0.5 * 0.94 * L, B = 0.25 * 0.87 * L, C = 0.053 * 0.87 * L. Here 0.94 and 0.87 are the wave speed factor of the flat feed. For example, for F = 93 MHz, A = 152 cm, A = 70 cm, A = 15cm.
The 300 ohmic TV antenna flat feeder of a long A + B + 1 cm was cut. Wipe the 1cm of the bottom end and insulate it, and the two core wires are welded together.
From the bottom of the bottom, a 5 mm long insulation stripper, the left wire is welded to the core wire of the 50 ohm coaxial cable, and the shielded wire of the coaxial feed line is welded. See the following figure C, D. (Adjust the impedance of the adjustable antenna of the length.)
From the bottom end, the left cable is cut off here 5mm, see below B.
Raise the coaxial cable to 4-5 circles of about 10 cm, fixed to c below, which constitutes Balun required for the antenna, see below C.
The top of the antenna is used with an insulated line to hang antenna for use, see the picture below.
The following figure is an example photo of the double line J pole antenna. A is the entire antenna hovered in the high-rise wall corner, B, C, D is the details of the antenna to enlarge the photo.
The two-line J pole antenna can be rolled as the following figure, which is easy to carry.
The important parameters describing the antenna efficiency are a standing wave ratio (SWR), the closer to the station, the better, 1.0 representing the reflected wave is zero, standing wave ratio. 1881.1.6 (corresponding to 5% power reflected back) is quite Ok, the standing wave ratio. 1882.2.5 (corresponding 20% power is reflected back), there is a danger of too large and burn the transmitter.
The standing wave ratio measures typically measures the output power and reflected power, and is therefore generally also referred to as a RF Power Meter. The figure below is a photo of a radio frequency meter; the TX terminal transmitter output, an ANT terminal antenna or a false load (down the chart) is a false load).
We use the devil No. 1 transmitter as a source, adjust its transmit power to 93MHz, will hold the two-line J pole antenna of the above method to stand in the basement (to reduce long-distance transmit power), change C The standing wave ratio of the antenna is measured. We also adjusted the transmitter's matching circuit to the maximum output power after changing C. The following makes our experimental results:
C (cm)
Output power (W)
Reflection power (W)
Standover
twenty four
4.8
1.7
3.8
twenty one
5.2
1.0
2.6
In
5.0
0.8
2.3
15
6.0
0.3
1.6
12
4.0
1.0
3.0
9
2.8
1.5
5.8
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