The radio equipment of deferent information needs any support electromagnetic wave aerial. Aerial is one kind turns can implement. When blast off, it changes the high frequency electric current of catapult into dimensional electromagnetic wave. When receiving, it sends receiver the electromagnetic wave changeover that intercepts and capture from the space into high frequency electric current again. The introduces radio to send and receive device culmination line principle with simple text and make. Whip antenna is pocket ultrashort radio, receive with blast off common pay aerial. But those who consider use environment is different, general the antenna that this machine matchs to have two kinds of different type is offerred choose. One kind is antenna of 1/4 wavelengh whip, another kind is small-sized screw antenna. Antenna of 1/4 wavelengh whip is one kind tenders by the common pull rod of knaggy composition line. The high frequency electric current that gives out with catapult is pulled open to produce resonance when the job. Theoretic, the length of antenna of the whip when resonance should be syntonic frequency 1/4 what grow relative to Ying Bo. But, because electromagnetic wave is in,the transmission speed in metallic lever is compared a bit small in air, the wavelengh that electromagnetic wave transmits on metallic lever is corresponding also a bit short, incident flogs the length of aerial wants to compare 1/4 wavelengh actually slightly some shorter. This shortens coefficient and working frequency, metallic shank diameter is concerned. Working frequency is tall, metallic shank diameter is big, shorten the value is great also. This telescopic antenna is average diameterBe 4. 5 centimeters, shorten coefficient is 0. 97, 1/4 wavelengh multiplies the central frequency that takes broadcasting station job to shorten with this coefficient is actual antenna length. Screw antenna screw antenna is a kind of new-style miniaturization communication antenna, it is particularly applicable to the pocket radio that uses in mobile communication. Because length is １ rice,much antenna grew really to pocket machine some, bring inconvenience to the person that use, use inadequate security around high-pressured electrical wiring especially. Designed total length technically to be less than telescopic antenna for this machine for this the small-sized screw antenna of 1/3. This kind of antenna already began to wait for a respect to win
application in communication and TV at present. Here focal point is weak formula of principle of the structure that talks ab
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out it, job, computation and the method that make. Structure: The span circumnutate with press metallic lead certain becomes gyroidal state, use insulating material to raise the axial direction of lever edge helix to prop up coil, of helix, the output of end and catapult carries join, open a way of other one aspect of the matter, made screw antenna. The product is to use diametical １ . 2 millimeter carbon steel silk, circle into average diameter to be １ on common lathe centimeter helix a certain number of circles, use sectional the heat that is wintersweet shape shapes polypropylene core lever raises drive out to rise. Be in charge of with fourth board balata outside helix sealed in case rainwater overflows corrode. Working principle: Small-sized screw antenna is system of a slow wave. Electromagnetic wave spends ｕ to compare the rate in air in the transmission involuntary discharge of urine on helix axial direction (it is C of velocity of light approximately) a lot of smaller, wavelengh is so corresponding also a lot of shorter, try to distinguish for as corresponding as working frequency wavelengh, be called the wavelengh in corkscrewed yarn " guide wavelengh " . By the graph １ can show its principle. Can think electromagnetic wave is along the metal corkscrewed yarn circles those who make direction travel with C of velocity of light approximately roughly now, when circling circuit to arrive at ｂ to nod from ａ dot along corkscrewed yarn when electromagnetic wave, the run that wave of actual electrify magnetism took S only on the axial of helix (pitch) , develop group of this one helix into the right-angled triangle on plane, criterion the transmission speed C that bevel edge represents corkscrewed yarn of electromagnetic wave edge, short orthogonal edge represents the transmission speed ｕ of axial of helix of electromagnetic wave edge. By the geometrical relation of the right-angled triangle ψ of ｎ of ｉ of ｓ of · of ｕ ＝ C is knowable (ψ horn is helix tangent and horizontal included angle) , because of ψ of ｓ ｉ ｎ < １ , so always ｕ is less than C of velocity of light, reason corkscrewed yarn is a slow wave system, it can decelerate the transmission speed of electromagnetic wave. Be like a screw antenna also make it resonance is in the antenna of 1/4 wavelengh, so it should be resonance is in of 1/4 " guide wavelengh " on, consequently the geometrical length gauge of screw antenna calculates formula: The length of screw antenna is equal to 1/4 " guide wavelengh " . "Guide wavelengh " concern with ｆ of frequency of S of spiral diameter D, pitch, job. There is very complex maths concern between them, be like screw antenna ｈ " D, at the same time D compares working wavelengh again a lot of smaller, can press the similar formula of the face has consideration: Computational Shi Yinggen occupies use condition, ｈ of D of diameter of appropriate of helix of make choice of, length (it is an unit with rice) , working frequency ｆ is decided by central frequency (with ' megahertz ' for the unit) , calculation of the form on the basis gives corresponding helix to encircle several N, of course the ｈ of make choice of should be compared D is a lot of bigger (10 times above) , circle the length that makes helix place use metallic wire to be able to press type calculates: D of π of · of ｌ ＝ N (2) the exemple is consistent and pocket frequency of machine center work is taken for 72. 7 MH ｚ , helix is smooth draw out ｍ of ｃ of １ of diametical D ＝ , hope antenna dimension does not exceed 25 ｃ ｍ , press (１ ) form calculation always encircles number for 79. 2, by (2) form calculation place is made an appointment with with lead length 2. 5 meters. Amateur makes the whip antenna that deserves to use with afore-mentioned pocket radio usable wall is large for 0. The thin copper pipe of 2 millimeter is self-restrained, tubal external diameter is in 7 millimeter of 5 ～ is advisable, length １ rice. If external diameter is some thicker, its length but slightly short 2 ～ 3 centimeters. The output of head and one catapult of copper pipe carries join, one diameter can be gotten in this the alveolus of 2 millimeter, from which derivative solder line and catapult are linked together, the plastic toothpaste of similar of usable caliber size builds the other one aspect of the matter of copper pipe seal, if have the telescopic antenna that length comparatives, can substitute. If the external diameter of telescopic antenna is thick, aerial length is OK still a bit a few shorter, if do not have a condition really, can be １ with length. 5 meters plastic skin lead will replace whip antenna. Of screw antenna make: Corkscrewed yarn can use appropriate means 0. 8 ～ １ . The enamel-insulated wire of 5 ｍ ｍ is circled make. The quality of work of enamel-insulated wire is not great to the function influence of screw antenna, between helix because voltage is not tall, use low strength commonly enamel-insulated wire of oil radical sex can. Those who require an attention is, the span between helix should keep consistent and be equal to design value. It is when working frequency 72. When 7 MH ｚ , pitch S is 3 millimeter, circle 80 rounds in all. Circle when making, but preexistence is with span on the metallic lever that a diameter controls for 9 millimeter 2. 5 millimeter is circled 85 rounds, the spring back of corkscrewed yarn considers after been circle, basically OK and contented center is apart from the requirement that is 3 millimeter, cut off redundant pen number again. The corkscrewed yarn that has circled raises drive out marvellous drive out to live with insulation, canal of division of hollow and club of the oxygen that be like annulus, organic glass club, electrical engineering model or fine bamboo lever. The aluminous silk that corkscrewed yarn returns usable diameter similar is circled make, aluminous nevertheless silk relatively cupreous silk is hard, spring back is big also, begin to circle when making, the center is apart from appropriate to obtain a little bit smaller, like 2. 2 millimeter is controlled, 3 millimeter is achieved through plastic after been circle, most above half helix comes back to be in a turn to tear open to the centre of a circle, rely on to prop up a club to withstand, see a picture 2. Can use thermoplastic bushing or thin rubber bushing cover the antenna that has made it is better to rise, corkscrewed yarn gets outside force and be out of shape in case. Screw antenna should with overall match ground job, make energy all blast off go out, or send the energy that receives into receiver entirely.
It is certain to flog aerial and screw antenna ministry have directional, center most in the energy on some a few direction namely, the result that receive or projects is best. When be being used so, can rotate aerial in order to achieve optimal communication result. Communicate actually the effect makes clear, when this machine deserves to grow whip antenna with １ rice, can level the land in 5 kilometer communicate reliably inside limits, the distance communicates to be 3 ～ when distributing line of helix die young 4 kilometer. It is OK also to receive afore-mentioned principles and computational formula the aerial parameter that draw gives the radio telemetering that works to go up in other frequency, remote control to send and receive equipment. In principle also can be used at TV, FM broadcasting to receive wait for radio device to go up.
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