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Because FM broadcasting content is rich, acoustic quality good, frequency is noisy the upper limit that the frequency frequency of the FM broadcasting with wide, good quality answers can amount to 15000Hz, especially FM stereo beamed appears, more accept masses favour, so numerous acoustics has a fever friend regards a kind of burgeoning news source as FM broadcasting. Although a lot of users are using a few top class FM tuner, but the letter that receives broadcasting station when place is miscellaneous than the adjacent, reception under the radio when sensitivity, the frequency signal of output cannot achieve the result of high fidelity, do not close even. The field compelled outdoor is normally more powerful than indoor field 15 decibel above, made erect open aerial relatively indoor aerial has " congenital advantage " , together with outdoor can the antenna of tall gain much unit with erect larger volume, when establishing FM-HiFi system so, want to choose ideal frequency modulation receiver not only, aerial also is cannot the part of oversight.
The FMA9901A receving antenna that article place introduces is the open aerial that is used technically at all sorts of FM tuner, since this antenna came out 1999 oneself, got domestic numerous FM broadcasting listens to lover reputably. This antenna by FM broadcasting special antenna is worn, amplifier of tall gain antenna, change the 5 much such as box of 16 meters of electric machinery, coaxial lines, power source to place composition.
Antenna of FMA9901A FM broadcasting uses amount to formula half brace up child model 3 unit antenna are worn, receive central frequency to be 100MHz, zhen Zicai is used eletroplate hollow aluminium is in charge of the 8mm after processing. The graph is the real measure that this antenna wears, for making reference.
Amplifier is magnified by circuit of FM filter wave, low noise circuit of dynatron, commutate, change control to circuit place composition. Graph the 2 principles that are this antenna amplifier pursue, signal is received by aerial after coming down, via impedance transformer B1 finishs 300 Ω - the impedance commutation of 75 Ω , input loop L1, L2, C1, comprise T respectively with C2, C3, L3 model low connect and connect filter high, make whole amplifier transmission bands is restricted to be between 80MHz-110MHz, divide the VHF signal beyond FM with filter, increase the interference rejection capacity of amplifier. The signal that receives as a result of aerial loses by force differ, lack fidelity to do not make the output n of amplifier exceeds n of the biggest output, together with amplifier is miscellaneous to the letter cannot undertake effective enlarge than extremely low faint signal, the NEC3356 that uses a low a confusion of voices only so (function is the same as 3358) microwave provides signal amplitude, connect filter output high via what C5, C6, L4 comprises, l6, C13 comprises circuit of depart of frequency of on any account, 12V is straight (hand in) shed voltage to add aerial amplifier through L6 (electric machinery) , as a result of the action of C13, 12V is straight (hand in) shed voltage to won't enter frequency modulation receiver, coupling of C13 of classics of frequency modulation signal enters frequency modulation receiver, because L6 has the effect with high frequency block, so frequency modulation signal won't enter power source.
Above antenna is worn and amplifier comprised tall gain sheet only direction is received, for can all-around tall gain is received, this antenna still installed steering gear, electric machinery uses electric machinery of synchronism of 12V communication permanent magnetism, exterior rotate speed is 4 turn / cent, torsional be more than 4 kilograms, the fault rate inside 1 year under 2% , because use job of low voltage small electric current, the 75 Ω coaxial that so electric machinery uses report and frequency modulation signal to all be in 14 meters with report, amplifier is transmitted on the line, make an operation very safe and convenient, need to press only K, d3 of turn light indicator shines, the alternating current of 12V is opposite through C12 electric machinery power supply, electric machinery M begins the work, interference won't generate to broadcast when rotating.
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