Two Stage Fm Transmitter

This Kit is a strong two step, 9V FM transmitter (Tx) delay a ramble of up to 1 kilometer in the known. It uses an RF transistor in its output step. Distance of transmission is critically relative on the unoccupied Conditions (in a architecture or out on the known), symbol of aerial used (separate wire or dipole), unoccupied voltage (12V is meliorate than 6V) and if the circumference is telling for consummation execution. The kit is constrained on a separate-sided printed circumference board (PCB). It has a silk protect plaster on top to aid rendering.On the infer tclose is a weld mask to succor in welding. Protel Autotrax and Schematic were used to delineation the board. ASSEMBLY INSTRUCTIONS Components may be acquired to the PCB in any adjust. It is usually easier to add the developed culmination components original then receipts to the taller components. The electret microphone should be inserted delay the pin united to the metal instance united to the indirect reprove (that is, to the infer or nothing voltage bprescribe of the circumference. ) This is remarkable delay a '-' wonder at the MIC on the circumference board printed plaster.To secure meacertain all the resistors must be inserted established up on one end. Be scrupulous to get the transistors environing the improve way. Note three summits: - the two 100n capacitors on the PCB own 0. 2" and 0. 1" spacing. We own put in components delay the improve spacing for tranquility of rendering. - we own replete prewound, pre-soldered enamel 6 alter & 8 alter wire twists. The legs should weld quickly to the pads of the PCB. However, pay eespecial study to the weld knee in instance all the enamel has not been ejectd. You may own to weld off or mark off prefer enamel from the ends of the two enamelled twists. a combination (or tap) is required from the intermediate of the L1 tinned copper wire twist to the pad remarkable TAP direct to the twist. Weld a ingredient of wire to the top of the intermediate alter as shown on the plaster. Then weld the other end to the pad quickly direct to the L1 twist. Open out the twists of L1 environing 1 mm asunder. Make certain none of the loops of the twist are tender the loop direct to it. CIRCUIT DESCRIPTION The circumference is basically a radio quantity (RF) oscillator that operates environing 100 MHz. Audio excusable up and amplified by the electret microphone is fed into the audio amplifier step built environing the original transistor.Output from the collector is fed into the low of the remedy transistor wclose it modulates the sonorous quantity of the tank circumference (L1 twist and the red adjustcap) by diversifying the combination capacitance of the transistor. Combination capacitance is a administration of the virtual variety applied to the low of the transistor T2. The tank circumference is united in a Hartley oscillator circumference. The terminal step built environing T3 amplifies the output RF wonderal. Let us observe at the separate blocks of the circumference prefer closely: The electret microphone: an electret is a burningly full dielectric.It is made by heating a ceramic symbolical, placing it in a magnetic opportunity and then allowing it to propitious conjuncture stationary in the magnetic opportunity. It is the electrostatic equiponderant of a burning magnet. In the electret microphone a slice of this symbolical is used as sever of the dielectric of a capacitor in which the diaphram of the microphone forms one dish. Sound prescertain agitates one of its dishs. The motion of the dish transmutes the capacitance. The electret capacitor is united to an FET amplifier. These microphones are mean, own excusable sensitivity, a extensive quantity reply and a very low require.First annotation step: this is a trutination self-biasing vile emitter amplifier. The 22n capacitor isolates the microphone from the low voltage of the transistor and barely allows alternating exoteric wonderals to ignoring. Oscillator step: full transmitter insufficiencys an oscillator to originate the RF conveyance waves. The tank circumference, the transistor and the feedback capacitor are the oscillator circumference close. An input wonderal is not insufficiencyed to stay the vibration. The feedback wonderal makes the low-emitter exoteric of the transistor diversify at the sonorous quantity.This causes the emitter-collector exoteric to diversify at the corresponding quantity. This wonderal fed to the aerial and radiated as radio waves. The call 'tank' circumference comes from the ability of the LC circumference to hoard disembodiment for vibrations. In a guileless LC circumference (one delay no hindrance) disembodiment cannot be past. (In an AC netexertion barely the resistive elements succeed expend electrical disembodiment. The guilelessly reactive elements, the C and the L, true hoard disembodiment to be returned to the classification after. ) Note that the tank circumference does not fluster true by having a DC virtual put abutting it. Confident feedback must be granted. Adexact Cap.The slots inbprescribe the adexact cap are outlined affect the chief of an arrow. The consummation capacitance estimate is when the arrow is in noticeable to the 12 o'clock composition. A 180o alter brings the adjustcap estimate to its partiality rated estimate. Delay trialation you succeed be able to raise up a board of entirety capacitance estimate (recall to add in the 10pF) to FM quantity. You can as-well transmute the quantity by altering the meacertain betwixt the twists of L1. Open out the L1 twist extensive asunder. The 10pF ceramic capacitor in analogous delay the red adexact cap succeed qualify you to air the Tx in the 98 MHz to 105 MHz ramble of the reciprocationable FM knot.If you use a preferable estimate (for copy, 27pF) you succeed agitate the quantity down towards the other end of the FM knot. This end generally has prefer reciprocationable stations in it. Terminal Annotation Stage: this RF step adds annotation to the RF wonderal. It insufficiencys an RF transistor to Kit 32. TWO STAGE FM TRANSMITTER do this efficiently. We use a Zetex ZTX320. L2 (an RFC radio quantity gag) and the 10p capacitor in analogous delay it are delineationed to imcouple harmonics from the circumference. Output energy from this step succeed be consummation when it is aird to fluster at the corresponding quantity as the anterior step.This can be executed delay the peaking circumference granted and picturesquely partially beneath. A mean (10pF) coupling capacitor on the aerial is optional to minimise the cheerfuls of the aerial capacitance on the terminal step LC circumference. (We own not used one in this circumference. ) Dipole Antenna. Greater ramble from the transmitter can be obtained by replacing the half-wave antenna (the extension of wire environing 160cm hanker) delay a dipole antenna. This is basically two wires fixed to two summits in the circumference which are bolstered 180o out of feature delay each other.Two such summits are the antenna summit and the confident reprove (the +9V trail. ) You can trial by trenchant the antanna wire in half, leaving half welded into the antenna summit and welding the otherhalf to the +9V pad. Summit the two wires in repugnant directions. Unoccupied Voltage. Output energy is as-well growthd by using a preferable unoccupied voltage. 9V is meliorate than 6V. The consummation unoccupied voltage for this Kit is resolute by the ZTX320. This is 15V but if you try this then the estimates of some hindrances succeed own to transmute. You can trial delay this.WHAT TO DO IF IT DOES NOT WORK Poor welding is the most affectly infer that the circumference does not exertion. Obstruct all weld knees scrupulously subordinate a cheerful unencumbered. Direct obstruct that all components are in their improve comcompose on the PCB. Did you add the combination from the intermediate of twist L1 to the pad remarkable TAP? Obstruct that the leads of the two twists L2 and L3 are not dry knees. Use a multimeter to obstruct this. Obstruct that you own not accidently formed a weld combination betwixt two pads which are direct to each other. Did you alter the switch 'on'.Check that you did not intertransmute the 4K7 delay the 47K resistors. Is the ZTX320 environing the improve way and in the T3 composition. Own you unquestionably open out the twists of L1? Some community own told us that each end of L1 should be bias aggravate and true environing tender the PCB. They as-well said that L3 should be open assubordinate a shabby. See us at http://kitsrus. com COMPONENTS Resistors, 5%, 1/4W: 100R brown ebon brown 470R yellow violet brown 4K7 yellow violet red 22K red red oramble 39K oramble unblemished oramble 47K yellow violet oramble 1M brown ebon exposed 1 1 1 1 1 2 1 Capacitors: Adexact cap 5-20pF, red 1 5. pF ceramic 1 10p ceramic 2 47pF ceramic 3 1nF ceramic 1 20nF or 22nF ceramic 2 100nF monoblock 2 RF transistor ZTX320 1 Mean wonderal transistor BC547 2 6 alter tinned copper twist 1 6 alter enamelled twist 1 8 alter enamelled twist 1 9V battery break 1 Electret microphone 1 PCB-mounted SPDT switch 1 Antenna wire 1. 6m k32 PCB 1 Peaking circumference 1 packet of components Kit 32. TWO STAGE FM TRANSMITTER Peaking Circuit. Kit 32. The tank circumference - twist L3 and the 47pF capacitor - insufficiencys to be aird in adtrue to get consummation energy output. It has to be aird to tally the quantity of the oscillator step 10pF cap, mutable capacitor and tapped L1 twist.The output “peaks” as the tank circumference is aird to tally the oscillator quantity. This peak can be measured on a multimeter. A peaking circumference (shown beneath) is barely an RF undeceiver that uses diodes to assault a capacitor. The voltage abutting the capacitor is measured using a voltmeter set to a low voltage ramble (2 or 20V). The circumference can be assembled delayout the insufficiency of a PCB. Barely weld the components quickly to each other. The output (abutting C2) should be united quickly to the voltmeter input using banana plugs or a couple of article clips bias to outline.The input to the peaking circumference is welded to the antenna wire cavity on the PCB, using a 5cm (2”) extension of wire. Switch the voltmeter to the 2V or 20V DC ramble. To air the tank circumference, barely agitate the alters of the tank twist L3 prefer assubordinate or closer unitedly until the lection on the voltmeter is a consummation. Note that the lection succeed be inferior conjuncture you are tender the twist. You succeed approximately unquestionably furnish that the twist alters own to be open very far assubordinate delay the developed alter at each end of the twist approximately tender the PCB. Once the output is a consummation, reagitate the peaking circumference and add the antenna.If you transmute the oscillator quantity by affecting the adjustcap then you succeed insufficiency to reiterate the peaking proceeding in adtrue to get consummation energy output. Want Prefer Range? You can get prefer ramble as a commerce off abutting inheritance by: • imcouple R5 to 100R • imcouple R7 to 47R • incrtranquility C7 to 470pFor a criticism of Kit 32 and abundant other FM transmitter kits on todays bargain see: http://members. tripod. com/~transmitters/begin. htm To discover the embracing system subsequently the exercise of two step Fm Tx see: http://www. csn. ul. ie/~francis/fyp_report/