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| J pole child (J-Pole) aerial blasts off by wave of a 1/2 yuan (part of right graph A) match with drive of wave of a 1/4 implement (part of right graph B) form, it is equal in value at from extreme drive occasionally extremely aerial, because of its conductor shows J model, reason calls J pole child. Right graph is the J that with antenna of 300 ohmic TV line of flat make a present of makes extremely child aerial (apply to 30W the following, abbreviation crewel J extremely child aerial) .
Crewel J extremely child aerial has make easily, facilitate carry, facilitate conceal wait for a characteristic. Introduce its to make move in detail below:
- Computational vacuum wavelengh: L=300/f rice, among them F is emissive frequency (megahertz)
- Computational length A, B, C: A=0.5*0.94*L, b=0.25*0.87*L, c=0.053*0.87*L. Here 0.94 with the coefficient of 0.87 velocity of wave that are line of flat make a present of. For example, to F=93MHz, a=152cm, a=70cm, a=15cm.
- The line of flat make a present of of antenna of 300 ohmic TV that cuts A+B+1cm of one end length. Will among them the 1cm that the bottom carries shucks insulation, be together solder of two core line.
- From the bottom upright upgrade measures C, 5mm a paragraph of long insulation shucks, the core line of on left line solder 50 ohmic and coaxial cable, the screen line of line of coaxial make a present of on right string solder, see figure below C, D. (adjust length C adjustable the impedance of aerial. )
- From the bottom upright upgrade measures B, 5mm of clipping of left line herein, see figure below B.
- Diameter of forgive of will coaxial cable about the 4-5 of 10cm circle, fixed it is under C, formed the Balun that aerial place needs so, see figure below C.
- With insulation line fasten in the top of aerial a crocodile is placed, use pensile antenna, see figure below A.
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| Next graphs are crewel J extremely child the example photograph of aerial. A is pensile the aerial whole in high-rise corner, b, C, D is the detail enlarge photograph of concerned antenna. |
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| Crewel J extremely child aerial can furl like following graphs come, facilitate carry. |
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The important parameter that describes aerial efficiency is standing wave comparing (SWR) , standing wave comparing is more adjacent 1 better; Wave of 1 delegates reflex is 0, standing wave compares <1.6 (corresponding the power of 5% is reflexed to come back) had comparatived, standing wave is compared > 2.5 (corresponding the power of 20% is reflexed to come back) when the risk that has emissive power is too great and burned-out emitter.
Standing wave outputs power than can measuring a watch commonly at the same time (Forward Power) with reflection power (Reflected Power) , because this is general,call radio frequency dynamometer again (RF Power Meter) . Next graphs are the photograph of dynamometer of a kind of radio frequency; The TX termination catapult of backside is outputted, ANT termination antenna or false load (what next graphs receive is false load) .
We use behead demon a catapult makes signal source, its emissive power moves 93MHz, the crewel J that will abstain by above method extremely child aerial stands hang in basement (in order to reduce remote emissive power) , the length that changes C measures the standing wave of aerial to compare. After changing C we also adjust a distribution road of catapult to make its output power the greatest at the same time. Make below our experimental result:
| C (cm) |
Output power (W) |
Reflex power (W) |
Standing wave comparing |
| 24 |
4.8 |
1.7 |
3.8 |
| 21 |
5.2 |
1.0 |
2.6 |
| 18 |
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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