make the 5W FM transmitter

veronica fm transmitter easily produced, stable performance, signal purity, without using specialized parts and ic, and a secondary test function in the absence of professional equipment to make your case easy to debug. It has two versions, 1 watt and 5 watts. 1 watt version for launch 3 km distance, the required power is 12-16v 200ma; 5-watt version for 8 km launch range, the required power is 12-16v 900ma. This article describes the 5-watt version.


The transmitter comes with a mixer, so you also fired from the cd and microphone audio signals. Transistor t1 is a microphone amplifier, variable resistors r1 and r2 adjust the volume (see section Debugging). Between the r8 and c21 oscillator, is to produce radio frequency signal components. Diode d1 is a so-called "varactor," the equivalent of an adjustable capacitor, which consists of the audio signal control, change the oscillator's oscillation frequency, played the role of frequency. c12, c13, and l1 determine the frequency of the oscillator. This oscillator is actually two inverting oscillator, each running around in 50mhz, when two signals combine, they become a 100mhz signal. Such circuits are much more stable than the single 100mhz oscillator. Oscillator signal from the t4, t6 zoom to 5w. T4 on the right in the circuit including the antenna impedance matching and low pass filtering. d2, d3, t5 auxiliary circuit is composed of debugging, it will sample the RF output signal to control LED d5, the output is high, d5 is also brighter.

The circuit itself does not bring stereo modulator, if you need to play stereo program, please refer to here to make stereo modulator.

Component List

r1 +2 10k adjustable
r3 820k
r4 4.7k
r5-7 220
r8 1.5k
r9 15k
r10 +11 1k
r12 33k
r13 +14 56
r15 +16 68k
r17 47
r18 270
r19 10
r20 22
r21 1.5k
r22 270
Capacitance: In addition to special assignments, the use of ceramic or mica capacitor.
c1, 2,7,
24,29 and 31 1n
c3-5, and 8 10u 16v electrolytic
c6, 18 and 30 220u 16v electrolytic
c9, 10 and 20 10n
c11 22p *
c12 47p *
c13 22p fine tuning
c14 and 15 15p *
c21, 25 and 26 65p fine-tuning
c22 100p
c23 15p
c24 33p
c27 1.8p
c28 5.6p
c32 and 34 47p
c33 22p
c35 and 38 1n
c36 220n
c37 100p
* C11, 12, 14 and 15 determine the oscillation frequency, it is best to use high-quality mica capacitors.
Coil: no skeleton with hollow type. To close around the wire diameter of 1mm or other rod in the cartridge, and then carefully stretched to the correct length, and to identify the two end coil shown in Figure 2.

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Figure 2a: coil around the correct method

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Figure 2b: l4, mrf237 pin
And antenna false load

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