500mW PLL FM Transmitter 88-108MHz
500mW PLL FM Transmitter 88-108MHz


500mW PLL FM Transmitter 88-108MHz


This PLL transmitter is controlled and the frequency is very stable and can be programmed digitally. Transmitter will work 88-108 MHz and output power up to 500mW. With a small change can set the frequency of 50-150 MHz. The output power is often set to several watts with transistors. So therefore I decided to build a simple transmitter with great performances. The frequency of this transmitter can easily be changed by software and space / compress air coil. This transmitter is the oscillator colpitts. Oscillator is a VCO (voltage controlled oscillator) which is set by the PLL circuit and PIC micro controller. This oscillator is called the Colpitts oscillator and voltage controlled to achieve the FM (frequency modulation) and PLL control.

T1 must be HF transistors to work well, but in this case I use a cheap and common BC817 transistor. LC tank oscillator needs to oscillate properly.
In this case the LC tank consists of L1 with the C1, C2, C3, and varicap BB139.
Coil parallel to the C1 and C2 in series. The same with the varicap and C3.
You may think that L is parallel to the [(C1 / / C2) + (Varicap / / C3)]
C3 will determine the value range VCO. Large value of C3 will be broader in the range VCO can be.
PLL and Microcontroller
Oscillator is made to work as a “Voltage Controlled Oscillator” VCO.
To control the frequency synthesizer circuit LMX 2306 has been added. The PLL circuit has a pickup coil (L2) is connected to pin 6.
This coil should be placed close to the coil L1 to take some of the energy oscillates.
The LMX2306 PLL in to use this frequency to adjust and lock the VCO to the desired frequency.
Systems also need to set the external reference crystal. In this case I use 12.8 MHz.
Pin 2 of MX2306 you will find the PLL filter to form a VM that is set voltage of the VCO.
The PLL tries to arrange so that the oscillator frequency Fout kept locked to the desired frequency.
The desired frequency programmed into the PIC EEPROM and clocked into the synthesizer (LMX2306) at power up.
I will below explain how to program the EEPROM to different frequencies.
In the pin14 of your synthesizer control output. In this output you will find a reference frequency for testing.
(I must warn you that the signal is not symmetrical in form. Pulsa positive only a few microseconds, so you will be hard to see on the oscilloscope.) I solved by connecting it to 74HC4020 (14-stage Binary Counter) to input pin 10 Hours. In Q0 (pin 9) you will have a symmetrical square wave with a frequency half since the circuit is a table. In Q1 pin 7 will be divided by 4, see data sheet for more information.
LF input
You want to send audio must be connected to the audio input (left schematic).
Will affect the signal and thus modulate the FM varicap RF carrier frequency.

A potentiometer P1 was added to adjust the depth of modulation (FM Wide or Narrow FM). You may have to play a bit with a value of P1 because it tends to modulate the lot. You may need to add the 500k – 1M potentiometer only. You test and find out for himself.

Buffer stage
Here you find other HF transistors and work in the class C.
Resistor R1 and resistor Re2 regulate the flow of DC. In this case I find that 9.1k will give a good output power and thus equal to 150. If you want to increase the power should be lower Re2. You can add another 150 ohm resistor in parallel.
In the table below I’ll show the output power with different voltages and resistor values of Re2.
I advice you to not run the transmitter with a high output power. Transistor I use is small and tends to be hot.
I advice you to run the unit from the 0 – to 200mW. At the transistor will 500mW pain …* smiles *
At the output you will find a network T. This “filter” will match the transmitter to the antenna impedance output stage.
You have two variables 60pF capacitors to tune the transmitter for best performance.
The antenna I use I a 1 / 4 wave whip antenna (wire) about 75cm long.
Smaller antenna types, but not so good performance as a dipole.
With a dipole you will be more long distance transmitter.
How long can I pass?
It is a very difficult question because the environment affects the transmission distance is very much.
In a city environment with concrete buildings transmitter will send maybe 200m.
I will send a proposed open 2000m.
I did the test and filed with 70mW output power into a “bad” whip antenna is placed in the room I can send 200-300m to a park without a problem.

Accurate LC Meter Capacitance Inductance Meter with 16F628 and LCD
Volt Ampere Meter with 16F876 Microcontroller and LCD display
Accurate LC Meter

Build your own Accurate LC Meter (Capacitance Inductance Meter) and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils and inductors. LC Meter can measure inductances starting from 10nH - 1000nH, 1uH - 1000uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging as well as reset switch and produces very accurate and stable readings.
PIC Volt Ampere Meter

Volt Ampere Meter measures voltage of 0-70V or 0-500V with 100mV resolution and current consumption 0-10A or more with 10mA resolution. The meter is a perfect addition to any power supply, battery chargers and other electronic projects where voltage and current must be monitored. The meter uses PIC16F876A microcontroller with 16x2 backlighted LCD.

50MHz 60MHz Frequency Meter / Counter with 16F628 & LCD
1Hz - 2MHz XR2206 Function Generator
60MHz Frequency Meter / Counter

Frequency Meter / Counter measures frequency from 10Hz to 60MHz with 10Hz resolution. It is a very useful bench test equipment for testing and finding out the frequency of various devices with unknown frequency such as oscillators, radio receivers, transmitters, function generators, crystals, etc.
1Hz - 2MHz XR2206 Function Generator

1Hz - 2MHz XR2206 Function Generator produces high quality sine, square and triangle waveforms of high-stability and accuracy. The output waveforms can be both amplitude and frequency modulated. Output of 1Hz - 2MHz XR2206 Function Generator can be connected directly to 60MHz Counter for setting precise frequency output.

BA1404 HI-FI Stereo FM Transmitter
USB IO Board PIC18F2455 / PIC18F2550
BA1404 HI-FI Stereo FM Transmitter

Be "On Air" with your own radio station! BA1404 HI-FI Stereo FM Transmitter broadcasts high quality stereo signal in 88MHz - 108MHz FM band. It can be connected to any type of stereo audio source such as iPod, Computer, Laptop, CD Player, Walkman, Television, Satellite Receiver, Tape Deck or other stereo system to transmit stereo sound with excellent clarity throughout your home, office, yard or camp ground.
USB IO Board

USB IO Board is a tiny spectacular little development board / parallel port replacement featuring PIC18F2455/PIC18F2550 microcontroller. USB IO Board is compatible with Windows / Mac OSX / Linux computers. When attached to Windows IO board will show up as RS232 COM port. You can control 16 individual microcontroller I/O pins by sending simple serial commands. USB IO Board is self-powered by USB port and can provide up to 500mA for electronic projects. USB IO Board is breadboard compatible.

ESR Meter / Transistor Tester Kit
Audiophile Headphone Amplifier Kit
ESR Meter / Capacitance / Inductance / Transistor Tester Kit

ESR Meter kit is an amazing multimeter that measures ESR values, capacitance (100pF - 20,000uF), inductance, resistance (0.1 Ohm - 20 MOhm), tests many different types of transistors such as NPN, PNP, FETs, MOSFETs, Thyristors, SCRs, Triacs and many types of diodes. It also analyzes transistor's characteristics such as voltage and gain. It is an irreplaceable tool for troubleshooting and repairing electronic equipment by determining performance and health of electrolytic capacitors. Unlike other ESR Meters that only measure ESR value this one measures capacitor's ESR value as well as its capacitance all at the same time.
Audiophile Headphone Amplifier Kit

Audiophile headphone amplifier kit includes high quality audio grade components such as Burr Brown OPA2134 opamp, ALPS volume control potentiometer, Ti TLE2426 rail splitter, Ultra-Low ESR 220uF/25V Panasonic FM filtering capacitors, High quality WIMA input and decoupling capacitors and Vishay Dale resistors. 8-DIP machined IC socket allows to swap OPA2134 with many other dual opamp chips such as OPA2132, OPA2227, OPA2228, dual OPA132, OPA627, etc. Headphone amplifier is small enough to fit in Altoids tin box, and thanks to low power consumption may be supplied from a single 9V battery.

Arduino Prototype Kit
RF Remote Control 433MHz Four Channel
Arduino Prototype Kit

Arduino Prototype is a spectacular development board fully compatible with Arduino Pro. It's breadboard compatible so it can be plugged into a breadboard for quick prototyping, and it has VCC & GND power pins available on both sides of PCB. It's small, power efficient, yet customizable through onboard 2 x 7 perfboard that can be used for connecting various sensors and connectors. Arduino Prototype uses all standard through-hole components for easy construction, two of which are hidden underneath IC socket. Board features 28-PIN DIP IC socket, user replaceable ATmega328 microcontroller flashed with Arduino bootloader, 16MHz crystal resonator and a reset switch. It has 14 digital input/output pins (0-13) of which 6 can be used as PWM outputs and 6 analog inputs (A0-A5). Arduino sketches are uploaded through any USB-Serial adapter connected to 6-PIN ICSP female header. Board is supplied by 2-5V voltage and may be powered by a battery such as Lithium Ion cell, two AA cells, external power supply or USB power adapter.
200m 4-Channel 433MHz Wireless RF Remote Control

Having the ability to control various appliances inside or outside of your house wirelessly is a huge convenience, and can make your life much easier and fun. RF remote control provides long range of up to 200m / 650ft and can find many uses for controlling different devices, and it works even through the walls. You can control lights, fans, AC system, computer, printer, amplifier, robots, garage door, security systems, motor-driven curtains, motorized window blinds, door locks, sprinklers, motorized projection screens and anything else you can think of.

Electronics-DIY.com © 2002-2024. All Rights Reserved.