FM Transmitter with Opamp
Circuit Of FM Transmitter with Opamp
Parts List:R1 4K7 R4 150K
R7 3K9 (2K7)
R2 4K7 R5 220R
R8 120R (82R)
R3 4K7 R6 4K7
All resistors except R8 are at least 0.25W rated. R8 is at least 0.5W rated
(the 0.6W metal film M-series from Maplin can be used for R1-R8).
C1 1n C4 22uF
C7 10n C10 1n
C2 4u7 C5 1n
C8 1n
C3 1n C6 10n
C9 33pF
VC1 5-60pF IC1 LM358
Q1 ZTX108
Notes:
L1 is 0.112uH (this tunes to the middle of the FM band, 98 MHz, with VC1 at its
centre value of 33pF). L1 is 5 turns of 22 swg enamelled copper wire close-wound
on a 5mm (3/16") diameter former. Alternatively, you can have a fixed 33pF cap
instead of VC1 and have L1 as an adjustable molded coil (eg UF64U from Maplin).
VC1 will give you a tuning range of 85 - 125 MHz, and a possible choice is the
Philips type polypropylene film trimmer (Maplin code WL72P). Two sets of
oscillator bias resistors are given, the ones in the brackets give about 20%
more RF power. Mike is our favourite Omnidirectional sub-mini electret (Maplin
code FS43W). Ant is a (lambda / 4) whip monopole (eg 76 cms of 22 swg copper
wire). Q1 is configured as a Clapp oscillator. Frequency modulation results from
the audio voltage changing the transistor's base-emitter capacitance.
Title: FM Transmitter with Opamp
electronic circuit
Source: unknown
Published on: 2006-01-15
Reads: 1323
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