![]() I have had some first hand experience of this problem. Body capacitance is equivalent to a 200pF capacitor shunted to earth, damping all oscillations. One final point, don't hold the circuit in your hand and try to speak. Although RF circuits are best constructed on a PCB, you can get away with veroboard, keep all leads short, and break tracks at appropriate points. Lengths of wire greater than 2 feet may damp oscillations and not allow the circuit to work. Actual range on my prototype tuned from 70MHz to around 120MHz. The tuning slug is adjusted to tune the transmitter. UF68Y and consists of 7 turns on a quarter inch plastic former with a tuning slug. The coil L1 was again from Maplin, part no. It is a two terminal ECM, but ordinary dynamic mic inserts can also be used, simply omit the front 10k resistor. I have used an ECM Mic insert from Maplin Electronics, order code FS43W. Both the transistor used here is general purpose 2N3904 transistor. ![]() The LC tank circuit (C4, L1) provides the base carrier oscillator. The 2nd transistor used in the circuit which is Q4 is the RF amplifier. The first transistor Q1 is an audio amplifier for the electret microphone. In this two transistor FM transmitter, a pre-amplifier is added which is formed by the Q2 transistor in the schematic below. Although not strictly RF transistors, they still give good results. The following shows the schematic diagram of the FM transmitter. I am sure you get the idea… Or you are able to just lightly tap the microphone whilst looking for the location with the signal in your receiver.I have used a pair of BC548 transistors in this circuit. I put this clock by the microphone which picks up the loud tick-tock. I use an old mechanical alarm clock (you realize, with these two big bells on it). To find the signal in your receiver, make certain there’s a signal coming into the microphone, otherwise the circuit will not work. Only in case you intend to use this circuit outside the house you might wish to choose much more temperature stable capacitors. Use any capacitor you’ve laying around, but NO electrolytic or tantalum caps. But generally almost nothing vital right here. The default for the capacitors kind is ceramic, preferably the npo 1% (low noise) kind or equivalent. It ought to be about 1/2 the power supply voltage (about 4 or 5volts). In the event you determine to substitute transistors with something similar you currently have, it possibly needed alter the collector voltage of Q1 by altering the value of R2 or R3 (because you change transistors, it changes this bias on the base of Q1). A little bit testing and patience might be in order.Īlmost all of the components values aren’t crucial, so you are able to attempt adjusting them to see what occurs. Then, using a non-conductive/non-metallic trimmer tool, fine-tune this capacitor to find the clearest reception. Set your FM radio for a clear, black spot in the lower end of the band (88MHz). ![]() The antenna is nothing more than a piece of 12″ wire or a piece of piano wire from 6″ to 12″. C2/C3 are electrolytic or can be tantalum types. C1/C4 and C5/C6 are ceramic capacitors, preferably NPO (low noise) types. To get a bit of tuning out of the coil you could put a 4-40pF trimmer capacitor (optional) parallel over the 1 uH coil, L1. C7 = 4-40pF trimmer cap (optional, see text)
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |