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1 Watt FM Transmitter Amplifier
This is a 1 Watt FM Transmitter amplifier with a good design that
can be used to amplify a RF signal in the 88 108 MHz band. It is
very sensitive if you use good RF power amplifier transistors,
trimmers and coils. It has a power amplification factor of 9 to 12
dB (9 to 15 times). At an input power of 0.1W the output will be 1W.
You must choose T1 transistor depending on applied voltage. If you
have a 12V power supply then use transistors like: 2N4427, KT920A,
KT934A, KT904, BLX65, 2SC1970, BLY87. At 18 to 24V power supply you
must use transistors like: 2N3866, 2N3553, KT922A, BLY91, BLX92A.
You may use 2N2219 at 12V but you will get an output power of 0.4W
maximum.
Calibration of the 1 watt fm power amp
Do not connect any RF source, just apply the power supply and
measure the voltage at point 1. Adjust R3 until you measure 0.7V.
Replace the antenna with 2 x 100 Ω 0.5W resistors in parallel at the
RF output. Now connect the rf signal that you need to amplify and
connect this RF Probe to the output.
Slowly adjust C1 in order to get the highest voltage value on the rf
probe. Now adjust R3 again to get 0.7 V at point 1. Now adjust C5
and C6 for maximum output voltage (must be between 12V to 18V).
Check the temperature of T1′s heatsink, if it is ok turn off the
power supply, disconnect the 2 resistors of 100 Ω and connect the
antenna (keep the probe connected). Apply the power and now adjust
again C1, C5 and C6 for maximum voltage indication on the probe.
You may use an ampermeter in order to check the current flow through
T1. This must not exceed 150mA at 12V and 100mA at 24V or the
transistor will burn. L2 and L3 coils must have an angle of 90
degrees between them. Dont use the 1W rf fm amplifier if you find
that you tv set is jammed and the laws of your country does not
allow the use of FM transmitters. |
