Circuit based on another project with
transmitter 2n2218, posted on the blog. Power supply be 6 to 12V Battery or good quality power supply, is recommended during test and adjust use of 9 or 12V battery.
The coil should be obtained four winding turns of enameled wire 22 AWG air core self sustained and 1cm diameter. Also in this case we connect the antenna between the third and fourth loop because it ensures greater stability in the transmission.
The variable capacitor should be with maximum capacitance 30-50 pF.
If you prefer you can use an adjustable coil of this FM receiver and put a fixed capacitor of 4.7pF instead of CV.
The
antenna can be a telescopic 80cm, a piece of stiff wire or a specific antenna for FM transmitter. Must be connected at the point marked by Ant and the coil is connected via C2.
component List
Resistor’s 1/4 Watt 5%
R1 4.7k – Yellow, Purple, Red, Gold
R2 8.2K – Grey, Red, Red Gold
R3, R6 47k – Yellow, Purple, Orange, Gold
R4 220k – Red, Red, Yellow, Gold
R5 1K – Brown, Black, Red, Gold
R7 6.8K – Blue, Grey, Red, Gold
R8 47 – Yellow, Violet, Black, Gold
Capacitor
C1, C9 100nF – (104, .1, 0.1, or 100n) Ceramic capacitor
C2 10pF (10p) – Ceramic capacitor
C3, C7 10nF (103, 0.01, 10n)- Ceramic capacitor
C4 1µF/16V – Electrolytic Capacitor
C5, C11, C12 10µF/16V – Electrolytic Capacitor
C6 1nF (102, 1n)- Ceramic capacitor
C8 100µF/16V – Electrolytic Capacitor
C10 4.7p (4p7, 4.7p)- Ceramic capacitor
CV 3-30pF -Trimmer
Semiconductors
IC1 LM741P – Integrated circuit operational amplifier.
Q1 2N2218, 2N2219 or equivalent NPN Transistor
Connectors
IN Connector P2 – Audio Input
B Connector for connecting the battery 6-12 Volts
ANT Point to connect the antenna
Several
L Coil – See text.
MIC Electret microphone
P Trimpot 10k
S1 Switch for activate the microphone