Mini FM Transmitter 2

This miniature transmitter is easy to construct and it’s transmissions can be picked up on any standard FM radio. It has a range of up to 1/4-mile (400 meters) or more, depending on the line-of-sight, obstructions by large buildings, etc. It is great for room monitoring, baby listening, nature research, etc.
L1 is 8 to 10 turns of 22 gauge hookup wire close wound around a non-conductive 1/4-inch diamter form, such as a pencil.
C4 is a small, screw-adjustable, trimmer capacitor.
Set your FM radio for a clear, black space in the lower end of the band (88MHz). Then, with a non-metallic/non-conductive trimmer tool, adjust this capacitor for the clearest reception. A little experimenting and patience may be in order.
Most of the parts values are not critical, so you can try adjusting them to see what happens.
If you decide to substitute transistors with something similar you already have, it maybe necessary adjust the collector voltage of Q1 by changing the value of R2 or R3 (because you change transistors, it changes this bias on the base of Q1). It should be about 1/2 the supply voltage (about 4 or 5v).

Parts List
R1,R4,R6 = 10K, C1,C2 = 0.1uF,  Q1,Q2 = 2N3904
R2 = 1M, C3 = 0.01uF, L1 = 0.1uH
R3 = 100K, C4 = 4-40pF
R5 = 100 ohm, C5 = 4.7pF
R7 = 1K

http://www.uoguelph.ca/~antoon/circ/fmt1.htm

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This entry was posted on Thursday, April 16th, 2009 at 7:13 pm and is filed under Frequency, Transmitter/Receiver. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.