There are electronic circuits that eventually get famous and receive up names, this is the famous case of this FM transmitter is called Veronica. The circuit is simple, it is a clear FM transmitter that does not use integrated circuits and is known for its extreme frequency stability and an FM signal clean and.
The FM transmitter Veronica is originally designed to have an output of 1 Watt, but on the Internet you will find several variants of circuit, and powers that can reach 10 Wattse com circuito PLL oscillator. Let's present the unique design of the transmitter Veronica here, with RF output 1 Watt.
Veronica FM Transmitter
This version of the FM transmitter is equipped with a mini-mixer ( mixer ) so you do not need to use an external mixer. The mixer consists of transistor Q1 which amplifies the microphone signal prior to being combined with the signal coming from the input “cd-player” which can be an MP3 player device, iphod, pc, cell phone or any other music player device. R1 and R2 are potentiometers , and are they going to adjust the sound level of the inputs.
The RF oscillator Veronica “apparently” is complex, it goes from R8 to the C21. Varicap diode D1 is, C12, C13 and L1 are the oscillator components that will determine the frequency of the transmitter. Are actually two oscillators working in the frequency 50 MHz in phase opposition and the two signals are combined to form the FM radio signal at a frequency of 100MHz.
This type of circuit is that the oscillator becomes stable transmitter Veronica. Na etapa final T4, one 2N4427 transistor is an amplified RF signal that is easily reach 1Watt. The circuit also comes with a RF output meter which comprises D5 and T5, that will help the tuning and checking if the circuit is transmitting, the more the RF output is high, will be the brightest LED D5.
R1, R2 Potentiometer 10K
R5–7 + 19 220r
R10 + 11 1k
R13 + 14 56r
R15 + 16 68k
C1, C2,C 7, C16, C17, C19,C24, C29 and C31 of 1n
C3, C5 and C8 10uF Electrolytic 25 Volts
C6, C18 and C30 220uF Electrolytic 25 Volts
C9, C10 and C20 10n
C11 22p *
C12 47p *
C13 22p trimmer
C14 C15 * 15p
C21, C25 and C26 65p trimmer
C27 and C28 1.8p
D1 (VARICAP ) KV1310
D2 and D3 1N4148
T1 and T5 BC548
T2 and T3 BF494
In fact L1 is composed of 6 equal and separate coils that join the PCI, make sure that the 6 The coils are identical as possible, if they have many differences, the transmitter can generate a signal poor. The wire coil is in American Wire Gauge (AWG).
L1 – 6 coils 2 1mm turns of wire (18AWG) with 5 millimeters in diameter and length 5 mm with air core .
L2 – 3 1mm turns of wire (18AWG) with 7 diameter mm, length 7 mm with air core.
L3 – 4 1mm turns of wire (18AWG) with 5 diameter mm, length 7 mm with air core.
L4 – 6 1mm turns of wire (18AWG) with 5 diameter mm, length 10 mm with air core.
The RF shocks, H1 can be done with a resistor of 33K ohms, with an enameled wire 0,2 millimeters 1/2 m in length wrapped around the resistor and welded at its terminals. Already the diodine varicaps, D1 is a “dual varicap” (with cathodes front). But it is not a critical component, almost any varicap diode will serve. But changes to components such as diode varicap, you may need to reset the circuit, for this you can increase the value of C11.
Transmitter Mounting Veronica
The transmitter must be built on a printed circuit board fiber, components should be placed as close as possible the plate, with very short terminals and soldiers. T4 is spaced from the other components you need for a heat sink.
Below the layout of the printed circuit board FM transmitter Veronica.
Below the placement of components on the printed circuit board FM transmitter Veronica.
Below is a printed circuit board of the FM transmitter mounted Veronica.
Connections microphone and CD must be made with connectors 3,5 mm and output BNC connector antenna use . The FM transmitter should be mounted in a shielded metal box grounded circuit. You can make some small holes in the lid over, to guarantee the flow of air over the heat sink transistor.
The supply voltage is between 9 e 16Volts, wherein 16volts with the RF output power is 1 Watt and 12Volts is 600mW and 200mW is 9Volts. Use a good power supply or battery to prevent the emergence of noise and frequency variations.
An important part of the project is the antenna, it must have an antenna cable assembly and the same impedance, and that the transmitter is adapted. Generally this is the weakest part of the transmitter system, with a good antenna and cable you will surely send all the power from the transmitter to the air.
Already an antenna botched, an old cable, poorly soldered connections and system without “marriage” the transmission loss is large and this signal “unirradiated” back to the transistor causing its burning. This small yet powerful FM transmitter has an impedance which is usually between 50 or 75 ohms, that means that the antenna has an impedance of 75 Ohm cable also have to have that impedance.
Completion adjustments and FM transmitter
1 – To adjust any type of transmitter is recommended to use a dummy load, you can use a resistor pack or 47 ohms, 50 ohms ou 68 ohms (non-inductive) or you can do this dummy load up 10 Watts, remembering that our transmitter has only 1 Watts. In the case of using the resistor, solde-the output of the antenna, in parallel with the capacitor C26.
2- With a key place all trimmers capacitors in the center position, ie in the middle of its course.
3- Connect an audio signal to the CD input.
4- Apply power to the FM transmitter.
5- D5 LED should be lit slightly, if it remains unlit try adjusting C21, if that does not light up check the circuit if there are no errors. The transmitter will broadcast around 98MHz.
6 – With a screwdriver or adjustment, no metal or insulated cable, start tune C21, C 25 and C26 for maximum LED brightness. Repeat this alternating sequence.
7- After obtaining the best performance of the FM transmitter, you will make the tuning of the desired frequency, no trimmer C13. Do this carefully up or down (depends on how often you intend to use) until the LED dim, but not completely erase.
8- Then, re-adjust the other trimmers C21, C25 and C26 until the LED reaches the highest brightness again. Repeat items 7 and 8 until you reach the desired frequency.
9- Check with a radio receiver or frequency counter if you are transmitting the desired frequency.
10 – If you have trouble reaching the desired frequency, particularly the edges of the FM, try working the coil L1. Carefully, tighten trims add more loops to lower or increase the frequency spacing of the turns to climb the frequency. Make sure that the six coils are identical.
11- Do not be upset or disappointed if the FM transmitter does not work at the beginning, transmitters usually require a little patience, RF is somewhat critical and unforgiving beginners.
Modifications FM transmitter
The original output transistor FM Transmitter Veronica is a 2N4427que has an output of 1 Watt, but users who used the trasistor 2N2219A had a better outcome, with an output of 2 Watts. Better yet replace the transistor 2N3866, are 4 Watts output with a voltage of 15Volts.
Attention! This equipment is to be used within the restrictions due, equipment for broadcasting are restricted and prohibited. Read the disclaimer Site and do not forget that illegal telecommunication activities is an offense under Law 9.472/97, Article 183, ie make the transmitter and use are the same, therefore fall into the same offense against the law.
Art. 183. Clandestinely develop telecommunication activities: Pena – arrest of two to four years, increased by half if there is damage to third, and lots of R $ 10.000,00 (dez mil reais). Single Paragraph. The same penalty who, directly or indirectly, compete for crime. The Criminal Code also provides for the crime in Article 336.
This scheme presented here is VHF transmitter and should only be used for testing and educational purposes and never as pirate radio. If you want to start with something simpler, I suggest the Micro FM Transmitter( Spy Bug SMD) or Micro FM Transmitter (The Spy).[Source]