Aerial launchs the importance of yuan of length
The length that you can discover to aerial emphasizes in the following introduction is 1/2 or 1/4 wavelengh, why? When the length because of aerial is incorrect, its impedance and design value are a lot of poorer, bring about emissive loss of efficiency. For example, the half wave idol that makes correctly extremely child the impedance of aerial is sex of 75 ohmic pure resistor, if its length halve, its impedance turns into 15-400j is ohmic, namely inductance of sex of 15 ohmic resistor, 400 ohmic capacitance. The resistor sex part of aerial impedance is significant to blasting off portion, and inductance part creates reflection wave only, energy feedback returns catapult. This one phenomenon is compared with standing wave commonly (SWR) description, standing wave comparing is more adjacent 1 better, wave of 1 delegates reflex is 0.
If need not cable of wire of make a present of, the inductance of aerial is usable and adscititious adjustable inductance or capacitance are sold, this calls of aerial match tuning. Of exemple of exemple as above shorten of the half occasionally extremely child aerial, the series connection inductance that can use a 400 ohmic inductance is sold go the sex appeal of 400 ohmic capacitance of aerial is fought, make aerial turns 15 ohm into pure resistor sex. But this asks the outputs amplifier impedance of catapult is less than 15 ohm at the same time, this has certain difficulty on circuit design, the frequency of aerial is wide also become very narrow.
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Electric wave is in the wavelengh in air is 300/f rice, among them F is emissive frequency (megahertz) , for example the wavelengh of 100 megahertz correspondence is 3 meters.
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Occasionally extremely child aerial
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| The half wave idol that the most commonly used antenna is central drive extremely child aerial, if pursue right,A place is shown. The method that make is: line of a blister copper (or copper pipe, aluminous canal, or the screen layer that uses coaxial cable) solder arrives on BNC electrical outlet. The length of blister copper line is 1/4 wavelengh about, namely 75/f rice, among them F is emissive frequency (megahertz) . The frequency that if you are unsure,you use, use 70cm. Such component needs two, b graph shows how to connect these two parts together. Line of above component blister copper should join with the center of BNC electrical outlet only, and the line of component blister copper below should join BNC crust.
Occasionally extremely child the former impedance of aerial is 75 ohm. As a result of occasionally extremely child two be semmetry partly (balance namely) , with coaxial cable (lopsided) the need when join has " 1:1Balance - lopsided transformer (Balun) " . The making way with this the simplest transformer is a cable circle a diameter about the 4-5 of 10-20cm circle.
Aerial should be perpendicular place, between cable and antenna should put apart at least 50cm sky is become.
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Use TV to pull stalk antenna to serve as FM idol extremely child aerial
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General dual role TV pulls stalk antenna to be able to use as FM half wave idol extremely child aerial is used. The Balun that this kind of antenna takes to be formed by high frequency transformer oneself commonly (the caddy that is like Zun Tu) , but should experiment beforehand this transformer whether the power that endures you to want to blast off (coil and magnetism core are not calorific can) . Another kind of Balun settles way is to use coaxial cable to regard make a present of as the line directly, its forgive diameter about the 4-5 of 10cm circle (consult above introduction) .
Aerial should be perpendicular place, every pull stalk to pull 75/f rice to grow, two pull stalk to should be become all the time line (pursue up A is same) , and should not be V form. Cable and antenna pull stalk not to answer parallel is stood by, and should put apart at least 50cm sky is become.
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