Frequency modulation (FM) beamed is received is in last few years, especially a of last year popular topic, because,this is FM broadcasting relatively amplitude modulation (AM) broadcast acoustic quality good, fidelity strong, program abounds tall, interference rejection sex, the most crucial is cost cheap, now although digital news source cans be found everywhere, wait like CD, VCD, DVD, but cost is high, musical software is the expenditure with endless brushstroke, and the reception of FM broadcast is free, reason is right income not of abundant and those who want to enjoy music is a lot of have a fever for friend, listen to frequency modulation stereo (FM ST. ) broadcast is best choice undoubtedly. But have a fever to be gone after friendlily never-ending, reception station is more, jump over optionally big, but this locality broadcasting station is finite after all, this is the origin that frequency modulation receives remotely.
Oneself also are frequency modulation has a fever one of friend, hobby frequency modulation is received already had ten years, summed up a few experience. Advanced a few years " the electron signs up for " the article that went up to publish a few concerned frequency modulation to receive a respect in succession. After introducing American path strange car to use digital tuning radio especially, caused a national frequency modulation to receive heat, also get climate, favourable geographical position, support of the people at that time, the cause with increasing FM broadcasting of each district of value whole nation, make burned friend numerously to join this to receive train. However what the thing does not imagine like us is so simple, appeared such or in that way problem, at this late hour, return phone ring ceaseless, letter is quite much, enquire such as select material to me, receive, the problem of the respect such as maintenance, suffer the editor's agreement additionally, carry a pen again, high fidelity of systematic introduction frequency modulation is received, the concerned knowledge of select material respect, make broad frequency modulation receives lover to be able to achieve what one wishes, the dream that round frequency modulation has a fever.
A complete FM broadcasting receives a system to if graph １ place is shown,be comprised, include outdoor and indoor two much. The part outdoor includes aerial wearing and aerial amplifier; Indoor part includes frequency modulation tuner, result to put symphonious case. Frequency modulation receiver is mixed by FM high frequency head in put composition of stereo decipher circuit. Below tries to be elaborated in detail respectively.
One, aerial
Aerial is the family status that receives a system, it is the first station, without aerial, again good receiver also does not receive signal, without good antenna, receive also be impossible implementation remotely. To facilitate everybody understands, we receive contrast with TV, be being received to TV because of everybody is quite familiar, and they are congeneric frequency modulation is deferent. The design of frequency modulation antenna, be equal completely at TV antenna, if the demand is not high, can replace frequency modulation antenna with open aerial of 5 channel TV directly. Aerial has the following 3 index:
１ . The gain of gain antenna is a when use demonstrative antenna to receive signal ability main index, it is compare decision of two fields place by the deflection of aerial and around radiate. Deflection is smaller, the reception of aerial capability is stronger, the interference that gets other way is smaller, this namely why aerial should aim direction, ability receives the consideration of clear picture and audio. The around radiate of aerial is compared, it is to show aerial around receives those who believe mark strength to compare, this value is greater, explain aerial function jumps over beautiful. Main unit brace up child aerial, have two the biggest receive a range, namely around comparing is １ : １ , how to increase around comparing, make directional more acerb, best method is to increase director and reverser, why is this just used when signal is strong only namely individual brace up child, and the account that uses much uniter antenna when signal is weak. Theoretic, director is more, gain is taller, and reverser only can, but director is overmuch, can affect bandwidth, mechanical intensity is poor also, installation size is enormous, so frequency modulation paragraph aerial uses 3 unit antenna commonly, do not cross 5 unit at most.
2. Direction pursues it is to express what the signal place of different way has aerial is right receive ability, the meaning of it and deflection is different. In principle should make the signal direction of half Zhen Zitian line and broadcasting station launcher perpendicular, but receive far signal in fact, because transmission is changed somewhat, likely when receive somewhat deviation, answer to had better be a standard with receiving the result actually. Of course what we ask is a direction not only, ask 360 ° whole way is received however, this produced much direction and whole way antenna. In fact, in front individual brace up child it is much direction antenna, if will two pairs brace up child perpendicular combination, became crossed omnidirectional antenna, author of this kind of antenna also has introduced so, but because its efficiency is low, gain is small, reason is used in signal weak area is very not appropriate. Only way is used namely turn to aerial, it has taller gain already, have good directional plan again, it can undertake hanging down to close directly with the signal that comes from any direction, score the biggest gain, it can raise letter a confusion of voices to compare, eliminate adjacent frequency interference to be the same as frequency interference even, it is the optimal option that our frequency modulation receives lover.
3. Bandwidth it is a target that expresses to receive frequency of frequency modulation signal. Transmission bands is wider, state its receive broadcasting station more, the frequency limits of FM broadcasting of our country regulation is 87. 108 MH of 5 ～ ｚ , total bandwidth is 20 MH ｚ , still belong to tape antenna, among them
＿ of ＿ ＿ ＿
Is heart frequency ＝ √ λ 1? λ 2 ＝ 97. 4 MH ｚ , take 98 MH ｚ commonly, if deflection some frequency paragraph, for instance low paragraph (98 MH of 88 ～ ｚ ) or high frequency paragraph (108 MH of 98 ～ ｚ ) , when designing aerial, some carries OK and intended liability, master neatly.
Anyhow, receiving FM broadcasting is to the requirement of open aerial gain wants tall, have whole way to receive (if other direction does not have broadcasting station, also but directional receive) , use convenient. General gain of 3 unit antenna is 7 ｄ B, 5 unit antenna can amount to 11 ｄ B. The FM9901A that the author used last year antenna, it is the 3 unit and special antenna that domestic head home receives a design by FM broadcasting, use power source case, can control aerial all-around roll is received, the result is right. Because calculation of design antenna dimension is complex, the making dimension of antenna of 5 unit frequency modulation gives out only below, see a picture 2, contain reference for lover.
Material: The aluminium of 10 ｍ ｍ is in charge of use ∮ , make by the graph, copper pipe is better, the diameter has been jumped over greatly more, but amount to is made in the turn brace up the period of the day from 11 pm to 1 am uses arenaceous bead fill first full, bend next make, break off so not easily, and sinuosity is smooth. Intermediate usable and same material joins, but the attention must be mixed in director the midpoint of reverser. Usable also insulating material joins, all do not affect the result.
2, aerial amplifier
Amplifier is the essential component that FM over-distance Cheng receives, without it, over-distance Cheng receives be impossible implementation. Its action is the faint signal that receives aerial undertakes enlarge, compare in order to raise letter a confusion of voices. Additional, average span gets the antenna that receives remotely very tall, need line of very long make a present of to introduce indoor, this has certain loss, another action of amplifier offsets the loss that place of line of transmission make a present of brings namely.
A of aerial amplifier main index is gain. Popularly is told, gain is a few taller, output n is corresponding a few taller, but noise also increases subsequently, lose especially signal is more such, when inputting strong signal, output n is exorbitant can make receiver crosses carry on one's shoulder again lack fidelity, produce block phenomenon, accordingly gain wants proper, control in 30 ｄ B commonly, those who need an attention is not to want to regard amplifier as all-purpose weapon, seemed to have amplifier, all problems be readily solved, there still are a lot of complex reasons here (hind article general is narrated) . Because of frequency modulation paragraph bandwidth only 20 MH ｚ , belong to tape amplifier, want advanced course to join corresponding belt to connect filter only can.
The principle that chooses amplifier is tall gain, low noise, had better take AGC function. Inchoate product all is 2 class or high frequency dynatron constitutes 3 level, noise is big; Later period product uses transistor of one class low noise to increase on one level compositive enlarge circuit, the commonnest is the form of PC1651 of μ of 2 SC3358 ＋ , this kind of form is chosen by a lot of manufacturer place. In recent years better is the circuit of AT415 ＋ A08 with use function index better, the author thinks this is at present first-rate is combined, accord with low noise, tall gain choose a principle. The QG836 amplifier that the author ever introduced is this kind of form. Be like conditional, can choose effect of field of 2 class double bar to be in charge of the amplifier that form, it is divided have inferior noise, outside taller gain, still have very strong fight overload ability, should be outside dividing integrated circuit, schism best choice, double bar canal can choose the K73, model such as BF964.
Actually, as long as it is the amplifier that uses on TV, all can use at frequency modulation paragraph, need only will before class belt connects filter to change BPF of unifinication of frequency modulation appropriative can, its appearance is like capacitance of a ceramics, but 3 cite a base, namely input, ground, output, its action is 88 ～ the signal filter beyond 108 MH ｚ is dropped, and frequency modulation signal is straightway, rose effectively to believe comparing of a confusion of voices. If do not buy this, usable inductance, capacitance is combined, if pursue,3 are shown.
Tell everybody again a bit, before the author paragraph the high frequency head that time experimented to be received with Yu Weixing will did aerial amplifier to obtain very good result. The satellite is received on full screen of used metal of high frequency head prevents pluvial structure, its in-house mixer stage and this brace up class eliminate need not. Interior has effect of 3 level field to be in charge of the circuit of high frequency enlarge that make, its receive frequency for 3. 4 ～ 4. 2 GH ｚ , it is frequency modulation paragraph a few times, gain tall, effect is good. Although interior has syntonic circuit, but signal of frequency of microstrip inductance exchange will tell be equivalent to straight lead only, advanced course joins BPF is very good amplifier. Of course the author was to do a test merely just, time is not long, its stability still has need checking test.
3, join of system of the part outdoor and erect
Had fine day line, amplifier, it is very important also that its join.
１ . Of aerial wearing and amplifier deserve to receive will tell commonly, impedance of the input of amplifier, output all is 75 Ω , and amount to brace up child impedance is 300 Ω , must use 4: The impedance of １ matchs implement (the 300 ／ on usable television electrical outlet of 75 match implement substitute) try to match. If join directly, loss is increased, original very faint already signal, have a loss again, its signal not smaller, because this should take seriously very,match a question. Although half brace up child impedance is 75 Ω , but itself machinery intensity is poor, and also put in １ with the coaxial cable of 75 Ω : The balance of １ matchs a question. Transmission line need not line of compressed make a present of and because former loss is too big,line of the make a present of that use a circle is, reason chooses the 75 Ω coaxial cable with lesser loss, use commonly 75 - 3 model, with 75 - 5 better, of course cost is some higher also. Aerial amplifier is installed commonly below aerial wearing 30 ｃ ｍ is controlled, also have those who install unifinication to form, if FM9901 antenna is this kind of form, solved problem of the snow that prevent rain at the same time.
2. Be like receiver to the join of receiver from amplifier is odd whip telescopic antenna, receive the silk of the copper intermediate of coaxial line only, outer screen net is empty. If finished product tuner, have 75 commonly Ω with 300 Ω two groups of antenna input terminal, can receive the 75 Ω terminal that attributes crimp kind, match correctly only, ability obtains the biggest n to input.
Be like erect open aerial, raise aerial height as far as possible, it is prep above ground commonly 6 ｍ above, prep above housetop 3 ｍ above. But also be not it is good to jump over Gao Yue, too efficient fruit becomes possibly instead poor, answer to decide erect height according to receiving the result actually, if circumjacent object is tall without aerial, install lightning rod even, make its good ground connection, lest be struck by lightning.
Many reader incoming telegrams will case inquiry: According to introducing some model it is good that aerial or amplifier receive the result, but use actually why to improve not quite, or the effect is poorer instead. Should say: Equipment is good, but also be of relative to character, this is concerned with use method, can might as well check looks up systematic join to whether have a problem. Next, the stand or fall that receives the result still has very big concern with surroundings, be like the height of launcher antenna, emissive power volume and the building all round are waited a moment, cannot treat as the same. Tell commonly, a mountainous area reception wants difference than Campagna, exceed especially receive remotely. Move aerial position sometimes a few meters, try a few dot erect more, the likelihood has very big difference. If can use open aerial to receive good broadcast, need not add amplifier again, amplifier is used undeserved when, it is source of a noise; Some is received remotely to achieve, use two amplifier to string together receive rise, must notice two amplifier are apart from 2 ｍ at least at this moment, have certain attenuation even, succeed very hard otherwise.
Oneself are located in Heilongjiang a mountainous area (north latitude 44. 7 ° , the east longitude 128. 2 ° ) , ever cooperated rare opportunity or machine of the Milky Way to get a few broadcasting station with crossed omnidirectional antenna. The effect is like Harbin goodly the 3rd broadcast that visit a station, the 8th of Changchun, the 4th of Jilin city, the others all is desk of circumjacent county town. But the literary like and other places of Beijing, Anhui, Wuhan, Hubei, Jiangsu, Zhejiang stage of other, still the foreign broadcasting station such as Korea, Japan, Russia belongs to over-distance Cheng to receive, this kind of stage is impossible that long-term stability is received, because the reflection of ionosphere and reflection place are formed, its field is strong ignore big ignore small, a little while unusually stable, clear, a little while noise rise from all directions, till disappear. Common law is: It is good that morning and evening receives the result, the summer is close friends than winter.
4, FM high frequency head
The sensitivity of frequency modulation receiver basically is decided by high frequency head, it is the first station of receiver. Usually, schism those who assemble is better than integrated circuit, two integrated circuit compare sheet again piece circuit is close friends. Be like the CXA1238 with common market, CXA1019, TEA5711 to wait all is odd a circuit of reception of a radio, collect is Gao Fang, medium put, demodulation (even result put) at an organic whole, because circuit is squeezed on a chip, certainly will accepts or reject somewhat. And odd a circuit of frequency modulation head, if TA7358, LA1185 is circuit of head of special frequency modulation etc, reason consistency is better, sensitivity is taller, it includes Gao Fang commonly, this brace up, mixing 3 parts, with circuit of head of appropriative frequency modulation so Jiashangzhong puts demodulation circuit, should be better combination, if common TA7358 ＋ TA8132, heart gives birth to PL757,wait. Schism assembly frequency modulation head is inchoate all be dynatron circuit, one level is put high, one class frequency conversion, better those who have independence this brace up. If change Gao Fang dynatron into field effect to be in charge of, criterion noise is reduced greatly, gain also can raise a few decibel. If want to increase gain further, it is insufficient that sheet relies on to increase the number that puts level high (because noise is right now big also) , must use tape tuning circuit, increase a return that choose frequency again before putting level high namely, such not only increased gain, and raised interference rejection ability and alternative, so advanced frequency modulation head is used 3 move even alterable electric capacity the stage, like radio of the frequency modulation on the car high frequency head all uses this to plant 3 move even alterable capacitance or inductance the stage, gao Fang uses effect of odd bar field to be in charge of, have independent Ben Zhenhe mixing, this namely why the reason with the taller than common radio sensitivity radio on the car. Can refer to our newspaper about circuit of car reception of a radio 1991 bound edition appendix. The sensitivity of high frequency head is the V that use μ comes denotive, accomplish the sensitivity of V of ≤ １ μ commonly, namely perfectly index.
About digital tuner (report is harmonious) , the alterable capacitance that just is an air station changed transfiguration diode, change the tension that is increased on diode, its capacitance also is changed subsequently. Such leave out the electric capacity with larger volume and complex drawing machine form, and can join key to accuse, remote control, went to the lavatory a lot of. The receiver of electric tuning contains liquid crystal commonly (or fluorescent) indication screen, use at showing the information such as sign of wave band, frequency, time, stereo, station, make receive be clear at a glance. Digital tuner also falls from hundreds of yuan now to just a little 100 yuan, frequency modulation receives lover to had better use tuner of this kind of number, especially preferential the high frequency head that chooses 3 transfiguration diode to assemble, but also do not think every counts word tuner sensitivity all tall, just be to use go to the lavatory. The American path strange car that introduced last year uses radio and homebred the Milky Way 883 A tuner all is used tape tuning high frequency head, sensitivity is very so tall, do not have goods to be able to be offerred at present regrettablly only. The author is in our newspaper this year the 10th period ever introduced two high-powered frequency modulation high frequency head, all be brand-new Japan is installed formerly, tuning of report of tuning of enlarge of effect of independent screen, field, tape is special have a fever first, its special place depends on cent paragraph receive, frequency limits VL: 150 MH of 70 ～ 176 ～ of of ｚ , VH 223 MH ｚ ; U paragraph: 770 MH of 475 ～ ｚ ; Outside dividing the frequency modulation wave band that can receive a standard, still can receive TV the audio of 3 channel above, include major supplementary channel, the very outstanding frequency modulation broadband that is rare receives a head.
Additionally the author recommends the circuit with a very superior performance again, see a picture 4, contain reference for lover. This is a schism adds compositive FM high frequency head, advantage of its collect both is a suit: After using effect of field of one class double bar to provide harmonious amplitude, FM is entered after network of classics choosing frequency again high frequency head is special integrated circuit AN7254, undertake Gao Fang, mixing outputs intermediate frequency 10. Signal of 7 MH ｚ , via 10. After the filter of 7 MH ｚ enters the week in frequency modulation to choose frequency further, enter integrated circuit to have one class beforehand in put, output pure intermediate frequency from ⑨ foot, again via 10. Evacuation of wave of filter of 7 MH ｚ is entered in put demodulation. Through above simple flow is narrated visible, 10. The intermediate frequency signal of 7 MH ｚ passed wave of 3 class filter, it may be said is pure and pure, its alternative, sensitivity all very outstanding; More god-given is AN7254 is divided outside having groovy function, its ⑧ foot still outputs voltage of Gao Fang AGC, the 2nd grid that adjusting control double bar is in charge of, in order to achieve the goal that automata puts gain high, avoid tall sensitivity to encounter the block appearance that strong signal place brings. The author thinks: The FM that this is a best show is high frequency head circuit.
|
|
5, had sensitivity tall before class is high frequency first, explain only had the capacity that receives over-distance Cheng weak signal. And how to come out demodulation of intermediate frequency signal, reductive into sound, achieve high fidelity, be very important and often uncared-for measure. This part circuit by in put, composition of circuit of decipher of demodulation, stereo, accessary and harmonious directive and stereo directive reach circuit of switch of odd ／ double sound. Main technique index has: Gain is put in, had jumped over higher; Harmonic is lack fidelity, lower better; Believe comparing of a confusion of voices, had jumped over higher; Stereo depart is spent, had jumped over higher. This part circuit basically is formed by integrated circuit, commonly used circuit has CX - A1238, TEA5711, TA8127, TA8132. These circuit, should input only 10. The intermediate frequency signal of 7 MH ｚ , the stereo frequency signal that can have right-and-left track is outputted, and these a few circuit all can deserve to receive AM circuit, periphery element is little, suit oneself to start work make, two circuit of other, demodulation is put in be like, output odd track signal only, enter sheet even piece decipher circuit, not as simple as still, and performance is steady.
The author recommends the M51535 circuit of 3 water chestnut of Japanese, applied circuit graph sees a picture 5. This is the sheet that this see function index is best up to now piece demodulation circuit, especially the choice of periphery component, all use cordial: CBB capacitance, Hei Jingang electroanalysises, village cropland ceramics, TDK10. 7 M. Try out makes clear, hue of the sound after demodulation is become pretty good, coronal with high fidelity absolutely not exaggerative. This makes I think of: Acoustics rub of chance become the order of the day today, why not the FM tuner high fidelity you phonic source rub one rub? Expenditure is not much, the likelihood thinks the results that be less than of purpose! The technical index of this circuit is: Harmonic is lack fidelity 0. A confusion of voices of 5 ％ , letter compares depart of 72 ｄ B, stereo to spend 45 ｄ B, visible function not common. But only stereo is indicated and indicate without tuning, and the above-listed all has tuning and stereo directive a few times. In addition, the stereo broadcast noise that receives weak signal is bigger. Nevertheless this circuit interior has automatic switch circuit, usable also hand uses switch direct switch arrives odd track position, turned clear odd track into broadcast at this moment. Its principle was to reduce bandwidth, rose to believe comparing of a confusion of voices, because broadcasting station frequency is the carrier wave frequency that points to it, its fluctuation still has the webbing signal of ｚ of 200 ｋ H, reason two stages are removed 0. 4 MH ｚ just won't produce interference, bandwidth of odd track broadcast is ｚ of 200 ｋ H, stereo bandwidth is ｚ of 400 ｋ H. Actually, when receiving broadcast, as a result of this locality stage little, span is very big, generate interference impossibly, and just is in when receiving a lot of far broadcasting station, have adjacent frequency inevitably or disturb with frequency, besides relying on aerial direction to eliminate, should be in 0. When interval of 3 MH ｚ produces interference, can use two 10. Series connection of filter of pottery and porcelain of intermediate frequency of 7 MH ｚ is used, in order to restrain adjacent frequency interference, can obtain better result commonly. Had better use one level right now beforehand in put make up for 10. The insertion of 7 MH ｚ loss, specific can refer to our newspaper bound edition is relevant 1997 article.
The configuration that puts about sound box and result already did not belong to the limits of article discussion, but reception frequency modulation program still has noise, can use result those who put fall circuit of a confusion of voices, assemble with LM1894 commonly, it has very good inhibition to FM broadcast noise, also can establish ties use, fall effect of a confusion of voices is double, be like result put without this circuit, might as well in be being added in tuner directly, make a magic figures drawn by Taoist priests to invoke or expel spirits and bring good or ill fortune actually high fidelity tuner. Combination of a gold recommends below: 3 unit remote control change direction take aerial amplifier TV of ＋ of special antenna of the FM outdoor uses MITSUMI of ＋ of remote control board stereo decipher is put in M51535 of ＋ of head of frequency modulation of three wave band board ＋ LM1894 falls circuit of a confusion of voices, totle drilling cost makes an appointment with 320 yuan. This covers combination, it may be said tuner of FM of a super tall acute whole wave band, it can store reach 90 broadcasting station, realize 70 ～ the frequency modulation signal of 770 MH ｚ is received, choose a stage to operate everything by the remote controller. Structure of head of frequency of stage high of triple wave of rice of rice at present and color television are high frequency the head is very similar, use the TV that imposes outfit remote control directly so flexible of remote control board is used, very convenient (be like leave out remote control board, but managing cost, but the hand is harmonious too gave or take a lot of trouble, must use tuning of potentiometer of appropriative much circle) . If add a TA7630 again board, so even size of sound of on any account, balance, volume also can remote control; If add one report to move AM package again, (receive frequency 0. 6 MH of １ ～ ｚ ) , can listen to the amplitude modulation broadcasting station of long, medium, shortwave again, of course cost raised accordingly again, but after all a minute of money a minute of goods, as a whole, sexual price is compared still is very tall.
Above is a bit experience that combines his to receive experience to write down. If your condition is better, can receive the broadcasting station program with deferent satellite, it also is frequency modulation is made, its acoustic quality amounts to CD level, but cannot use common radio demodulation, however appropriative satellite receiver. At present a １ . The imitate of 5 ｍ covers a station only 449 yuan, word of one a cycle of songs in a traditional opera is covered also only more than 1000 yuan, before comparing a few years of petty gain are much, its receive the result very stable, do not suffer any interference, 24 hours round-the-clock broadcast. At present imitate is covered ten when use audio subcarrier to convey central platforms that reach a province can be gotten in the station broadcast (partial program needs decipher of Li Yin decoder) , and the number covers a station, 449 broadcast can be received on 2 satellites of Asian only, include bandstand of partial foreign country, it is stereo for the most part, its acoustic quality is quite good. Domestic program all is centered on satellite of date of Xin Nuo １ now, although image is added close, but broadcast is open still, among them broadcasting station of central people broadcast 7, １ of China International broadcasting station is covered, the 3rd central literary frequency modulation is stereo, the broadcast that visit a station more than 30, and receive this satellite signal to need only 0. 6 meters of antenna, it is national all-pervading village village opens a project. We can see approximate DVD picture not only, return the audio that can hear CD level and broadcast, crucial signal is very stable. Of course, also have satellite of broadcast of frequency of special Yu Yin -- Asian star, already launched the success that decide a dot now, but receiver is too expensive, we are consumed at all at present do not rise. Original figure receiver is to use those who watch digitlization TV program, and we use it when the radio now, it seems that waste one's talent on a petty job, but as receive broadcast of high quality frequency, also can yet be regarded as a kind of better attempt.
|
Our other product:
