---------------------------------------------------------------------- This is a simple FM wireless microphone. It will transmit about a mile. ___ ______________________________________________________________ \|/ ___ ) | | | | | | | --- ) R ___ R R | ----- |_||__| C10 ) L1 4 --- C3 5 7 | --- || | ) | | | | ___ C6 ----- B1 C1 ------- | | | | --- --- 9VDC |_____ | | C9 __R6__ ---- | | | \ Q1 | | | | | | | | | \|______|_______|__|(__| Q2 | R | | | ___ /| | | |( \ | C5 8 | | | C2 --- / BF199 | | \|___|__|(___| _+_ | | |____V R | /| |( | --- | o | 2 ___ / BC183C | | C7 | \ | | C4 --- V | | | \ S1 R | | |_______ MIC / \ | | \ 1 | | | | \_/ | | O | | | R _+_ | | | | | | | 3 --- C8 | | | | | | | | | | | | | --------------------------------------------------------------- R1 = 100 ohms C1 = 1.5 pf NPO ONLY Q1 = BF199, ECG 229, R2, R4 = 10K ohms C2 = 100 pF, NPO ONLY 2N5179 or eq. R3 = 1K ohms C3, C4 = 330 pF NPO Q2 = BC183C, ECG123AP R5, R7 = 47K ohms C5, C9 = .1 uF 2N4401 or eq. R8 = 4.7K ohms C6 = .001 uF NPO ONLY L1 = approx. 1 uH M1 = electret mike C7 = 22 uF electrolytic S1 = SPST switch B1 = 9V battery C8 = 6.8 uF electrolytic C10 = 10 - 40 pF trimmer capacitor. The coil L1 is so small that in the PC board version of this, it's just a coil etched on the board with traces. I think I breadboarded it with about four or five turns of bell wire around a pencil and that made about the right value. You tune the sucker with the adjustable cap C10. If I remember, the transistors are garden variety ones, though I think Q1 was reasonably high frequency. I was feeding in a signal other than an electret microphone. This is neat to use with a cheapo FM walkman-type radio for cheap telemetry. (We were actually going to build a device to transmit strain gauge signals from someone's teeth over a whole day's time, and it was to be small enough to be relatively unnoticed INSIDE THEIR MOUTH the whole time. Never did get the O.K. to proceed with that one. Working for university research gets pretty strange sometimes.)