Two Stage Fm Transmitter

This Kit is a strong two rank, 9V FM transmitter (Tx) delay a stroll of up to 1 kilometer in the unconcealed. It uses an RF transistor in its output rank. Distance of transmission is critically relying on the uncounted Conditions (in a fabric or out on the unconcealed), character of aerial used (unique wire or dipole), uncounted voltage (12V is emend than 6V) and if the circumference is keen for climax act. The kit is fabricated on a unique-sided printed circumference consultation (PCB). It has a silk harbor coat on top to aid fabric.On the accountfruit thither is a condense mask to acceleration in condenseing. Protel Autotrax and Schematic were used to plan the consultation. ASSEMBLY INSTRUCTIONS Components may be added to the PCB in any direct. It is usually easier to add the lowest top components primitive then avail to the taller components. The electret microphone should be inserted delay the pin aapprove to the metal subject aapprove to the disclaiming reprove (that is, to the account or nothing voltage bprescribe of the circumference. ) This is notefficacious delay a '-' proof at the MIC on the circumference consultation printed coat.To economize extension all the resistors must be inserted established up on one end. Be regardful to get the transistors environing the emend way. Note three sharp-ends: - the two 100n capacitors on the PCB feel 0. 2" and 0. 1" spacing. We feel put in components delay the emend spacing for repose of fabric. - we feel gifted prewound, pre-soldered enamel 6 hinge & 8 hinge wire spirals. The legs should condense undeviatingly to the pads of the PCB. However, pay appropriate care to the condense alliance in subject all the enamel has not been abstractd. You may feel to condense off or grate off exalt enamel from the ends of the two enamelled spirals. a union (or tap) is required from the intermediate of the L1 tinned copper wire spiral to the pad notefficacious TAP present to the spiral. Condense a share of wire to the top of the intermediate hinge as shown on the coat. Then condense the other end to the pad instantly present to the L1 spiral. Disperse out the spirals of L1 environing 1 mm partially. Make trusting none of the loops of the spiral are pathetic the loop present to it. CIRCUIT DESCRIPTION The circumference is basically a radio abundance (RF) oscillator that operates environing 100 MHz. Audio choice up and amplified by the electret microphone is fed into the audio amplifier rank built environing the primitive transistor.Output from the collector is fed into the disingenuous of the cooperate transistor whither it modulates the sharp abundance of the tank circumference (L1 spiral and the red clipcap) by altering the alliance capacitance of the transistor. Alliance capacitance is a administration of the possible estrangement applied to the disingenuous of the transistor T2. The tank circumference is aapprove in a Hartley oscillator circumference. The decisive rank built environing T3 amplifies the output RF proofal. Let us observe at the specific blocks of the circumference exalt closely: The electret microphone: an electret is a steadyly entrustd dielectric.It is made by heating a ceramic representative, placing it in a magnetic scope and then allowing it to hopeful conjuncture quiescent in the magnetic scope. It is the electrostatic equipollent of a steady magnet. In the electret microphone a hunch of this representative is used as keep-akeep-secret of the dielectric of a capacitor in which the diaphram of the microphone forms one mess. Sound prestrusting propels one of its messs. The propel of the mess qualifys the capacitance. The electret capacitor is aapprove to an FET amplifier. These microphones are mean, feel palliefficacious sensitivity, a remote abundance confutation and a very low require.First annotation rank: this is a trutination self-biasing vulgar emitter amplifier. The 22n capacitor isolates the microphone from the disingenuous voltage of the transistor and solely allows alternating ordinary proofals to ignoring. Oscillator rank: integral transmitter deficiencys an oscillator to produce the RF carriage waves. The tank circumference, the transistor and the feedback capacitor are the oscillator circumference hither. An input proofal is not deficiencyed to maintain the oscillation. The feedback proofal makes the disingenuous-emitter ordinary of the transistor alter at the sharp abundance.This causes the emitter-collector ordinary to alter at the identical abundance. This proofal fed to the aerial and radiated as radio waves. The designate 'tank' circumference comes from the piiveness of the LC circumference to hoard earnestness for oscillations. In a guileless LC circumference (one delay no opposition) earnestness cannot be lost. (In an AC netfruit solely the resistive elements earn scatter electrical earnestness. The guilelessly reactive elements, the C and the L, true hoard earnestness to be returned to the rule posterior. ) Note that the tank circumference does not excite true by having a DC possible put despite it. Actual feedback must be supposing. Clip Cap.The slots inbprescribe the clip cap are patternd approve the guide of an arrow. The climax capacitance rate is when the arrow is in peaked to the 12 o'clock composition. A 180o hinge brings the clipcap rate to its restriction rated rate. Delay assumption you earn be efficacious to raise up a tefficacious of whole capacitance rate (mind to add in the 10pF) to FM abundance. You can as-well qualify the abundance by altering the extension betwixt the spirals of L1. Disperse out the L1 spiral remote partially. The 10pF ceramic capacitor in equidistant delay the red clip cap earn enefficacious you to melody the Tx in the 98 MHz to 105 MHz stroll of the wholesale FM knot.If you use a amend rate (for stance, 27pF) you earn propel the abundance down towards the other end of the FM knot. This end generally has exalt wholesale stations in it. Decisive Annotation Stage: this RF rank adds annotation to the RF proofal. It deficiencys an RF transistor to Kit 32. TWO STAGE FM TRANSMITTER do this efficiently. We use a Zetex ZTX320. L2 (an RFC radio abundance stifle) and the 10p capacitor in equidistant delay it are planed to refer harmonics from the circumference. Output piiveness from this rank earn be climax when it is melodyd to excite at the identical abundance as the preceding rank.This can be produced delay the peaking circumference supposing and feeling partially underneath. A mean (10pF) coupling capacitor on the aerial is optional to minimise the pi of the aerial capacitance on the decisive rank LC circumference. (We feel not used one in this circumference. ) Dipole Antenna. Greater stroll from the transmitter can be obtained by replacing the half-wave antenna (the extension of wire environing 160cm crave) delay a dipole antenna. This is basically two wires fixed to two sharp-ends in the circumference which are unsettled 180o out of deportment delay each other.Two such sharp-ends are the antenna sharp-end and the actual reprove (the +9V footprint. ) You can trial by sardonic the antanna wire in half, leaving half condenseed into the antenna sharp-end and condenseing the otherhalf to the +9V pad. Sharp-end the two wires in facing directions. Uncounted Voltage. Output piiveness is as-well extensiond by using a amend uncounted voltage. 9V is emend than 6V. The climax uncounted voltage for this Kit is decided by the ZTX320. This is 15V but if you try this then the rates of some oppositions earn feel to qualify. You can trial delay this.WHAT TO DO IF IT DOES NOT WORK Poor condenseing is the most approvely discuss that the circumference does not fruit. Bridle all condense alliances regardfully underneathneath a good-natured-natured unweighty. Present bridle that all components are in their emend comcompose on the PCB. Did you add the union from the intermediate of spiral L1 to the pad notefficacious TAP? Bridle that the leads of the two spirals L2 and L3 are not dry alliances. Use a multimeter to bridle this. Bridle that you feel not accidently formed a condense union betwixt two pads which are present to each other. Did you hinge the switch 'on'.Check that you did not interqualify the 4K7 delay the 47K resistors. Is the ZTX320 environing the emend way and in the T3 composition. Feel you truly disperse out the spirals of L1? Some race feel told us that each end of L1 should be leaning balance and true environing pathetic the PCB. They as-well said that L3 should be disperse partially a mean. 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 ostroll 39K ostroll unspotted ostroll 47K yellow violet ostroll 1M brown ebon bleak 1 1 1 1 1 2 1 Capacitors: Clip 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 proofal transistor BC547 2 6 hinge tinned copper spiral 1 6 hinge enamelled spiral 1 8 hinge enamelled spiral 1 9V battery split 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 - spiral L3 and the 47pF capacitor - deficiencys to be melodyd in direct to get climax piiveness output. It has to be melodyd to two the abundance of the oscillator rank 10pF cap, variefficacious capacitor and tapped L1 spiral.The output “peaks” as the tank circumference is melodyd to two the oscillator abundance. This peak can be measured on a multimeter. A peaking circumference (shown underneath) is barely an RF guide that uses diodes to entrust a capacitor. The voltage despite the capacitor is measured using a voltmeter set to a low voltage stroll (2 or 20V). The circumference can be assembled delayout the deficiency of a PCB. Barely condense the components undeviatingly to each other. The output (despite C2) should be aapprove undeviatingly to the voltmeter input using banana plugs or a two of monograph clips leaning to pattern.The input to the peaking circumference is condenseed to the antenna wire hole on the PCB, using a 5cm (2”) extension of wire. Switch the voltmeter to the 2V or 20V DC stroll. To melody the tank circumference, barely propel the hinges of the tank spiral L3 exalt partially or closer coincidently until the balbutiation on the voltmeter is a climax. Note that the balbutiation earn be inferior conjuncture you are pathetic the spiral. You earn approximately unquestionably discover that the spiral hinges feel to be disperse very far partially delay the latest hinge at each end of the spiral approximately pathetic the PCB. Once the output is a climax, repropel the peaking circumference and conjoin the antenna.If you qualify the oscillator abundance by melting the clipcap then you earn deficiency to relate the peaking act in direct to get climax piiveness output. Want Exalt Range? You can get exalt stroll as a dealing off opposite steffectiveness by: • refer R5 to 100R • refer R7 to 47R • incrrepose C7 to 470pFor a criticism of Kit 32 and manifold other FM transmitter kits on todays dispense see: http://members. tripod. com/~transmitters/begin. htm To peruse the ample assumption astern the agency of two rank Fm Tx see: http://www. csn. ul. ie/~francis/fyp_report/