Model the characteristic of aerial:
J antenna calls Polack aerial again, its characteristic is radiation angle of elevation low and have certain gain, efficiency is 1/4 GP antenna is duple. J antenna the part above is radiation paragraph, the part of below is to match paragraph. The impedance that adjusts good J antenna is pure block 50 Europe, can join with 50 Ω coaxial cable directly. As a result of its draw materials is made easily simple, got the jubilation of a lot of HAM.
See a picture one:
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Feed nods receive a standard:
The core line of 50 Ω coaxial cable receives point of long side feed, cortical receive point of short edge feed.
The adjustment of standing wave:
The effect that J antenna SWR suffers an environment is bigger, the place that feed chooses is installing the position actually to adjust with standing wave watch.
J antenna calculates: Http://www.packetradio.com/jpol.htm
Use the departmental measure of software calculative J antenna according to the graph: (Rice)
Frequency A B C D
7.0500 30.480 10.116 0.994 0.951
14.175 15.161 5.032 0.494 0.472
21.400 10.040 3.331 0.326 0.314
28.200 7.620 2.530 0.250 0.238
29.600 7.260 2.411 0.238 0.226
50.000 4.298 1.426 0.140 0.134
145.00 1.481 0.491 0.049 0.046
435.00 0.494 0.165 0.015 0.015
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Of J antenna all sorts of is out of shape:
Graph 2: V/U double paragraph of J antenna by Chan Pin paragraph J antenna develops and come, the feed pattern that double Duan Pi matchs is finished by cable of coaxial of two paragraphs of 50 Ω . 0.7 meters paragraph a paragraph of cable that grows with 1024mm, 2 meters paragraph a paragraph of cable that grows with 340mm, join closes a road to T form implement hind, introduce with 50 Ω cable indoor.
Graph 3: The J that line of 300 Europe make a present of does antenna, draw materials is easy, facilitate carry. Also apply to short wave band likewise.
Graph 4: Amount to brace up child J antenna, amount to share increased half can increase gain. If increase half to be about to add directly,turn over photograph coil, after amount to comes over, shortened already length rose to oppose photograph action again. Conception is clever!
Graph 5: 0.7 meters of amount to brace up child J antenna, the making data of UHF antenna.
Graph 6: 5/8 J antenna, the principle pursues together 4, it is feed method differs only.
Graph 7: Super J antenna, the principle pursues together 4, just match with hairpin replaced turn over photograph coil.
Graph 8: Adjustable the J of SWR antenna, the screw that uses department of 1/4 Duan Ding adjusts standing wave, convenient.
Graph 9: J combination function of 8 wood antenna and the YAGI of 3 unit are similar, it is feed manner varies somewhat only. Still one is plant is to will gather up leather antenna is put in radiation brace up child place, of make it gather up Pi Bamu antenna, principle very much the same. But lost complete to characteristic. Each takes what he needs.
Anyhow J antenna still has a lot of forms, still also be in constant change. Hope draw inferences about other cases from one instance adds authority ceaselessly, innovation goes the Chinese's antenna.
Note: (text material all comes from Internet) BD1HP
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