PLL FM Transmitter

type="html">Dual-speed PLL designed for wideband FM transmitter.

Power supply: 8-15 V stabilized, 40 mA
Frequency range: 82,5-108 MHz
Step frequency: 100 kHz
RF input voltage range: 10-500 mV
RF input impedance: 135 ohm

Parts list:
C1, C12 - 2,2 nF (ceramic)
C2, C9 - 10 nF (ceramic)
C3 - 47 uF (electrolytic)
C4 - 10 uF (tantalum)
C5 - 0,47 uF (electrolytic)
C6, C11 - 100 nF (ceramic)
C7 - 1 nF (ceramic)
C8 - 220 uF (electrolytic)
C10 - 22 pF (ceramic)

R1 - 1k
R2 - 4k7
R3, R4, R5, R7 - 10k
R6 - 1k (optional)
R8 - 47k (optional, see below)

IC1 - SAA1057
IC2 - PIC16F84 (programmed) + socket
IC3 - 78L05
X1 - 4 MHz crystal
D1 - LED diode (optional)
Tl1 - button (optional)
jumpers or DIP switches

Software for the IC2:
pll16f84.asm, pll16f84.hex. Oscillator type: RC, watchdog: ON.

Jumpers/DIP switches setting: see project documentation or download user-friendly program!


The Tl1 button resets the unit. Press it after frequency set. The unit provides a reset on power-up, so you don't need to use the button.
The D1 LED indicates the tuning cycle is done (after one second from reset). It's not needed to use it and the R6 resistor.
The R8 resistor provides a minimal voltage of about 2 V on the PLL output. Use this resistor if the transmitter's oscillator doesn't work if the tunning voltage is below this value (mainly after power-up). Place the resistor over the R3.


* Output of the PLL should not be directly loaded with big capacities (over about 0,3 uF). The PLL loop may be unstable. This applies to some unknown transmitters.

Download Project Documentation

RF Power Amplifier for iPOD Stereo FM transmitters 1W

type="html">The schematic show you a RF amplifier with very high gain. The feeding RF signal enter C9 to transistor Q1 which has a self biased working point. The gain and working point is set with the two resistors R1 and R2. FB1, C5, C6 works as filter for rejecting RF to power line. Q1 has a gain about 15dBm. The output signal can be found a the collector which then enter a second amplifier stage Q2. This stage also has a self biased working point. The gain is set by the resistors R3//R4 and R5//R6.

Why do I have 2 parallel resistors like that?
It is because I want to be able to change the gain of the amplifier. On the PCB below you will see that I only have 2 pads for the resistors. When I want to resistors I solder the two resistors R5 and R6 on top of each other and the same with R3 and R4.

I advice you to start building without R3 and R5 and test the unit. If you want you can then add R3 and R5 later to obtain max gain of this stage.
Q2 has a gain of 12 dBm. FB2, C7, C8 works as filter for rejecting RF to power line.

The last amplifier stage is based around the transistor 2N3866. This transistor has low input impedance.
I match it by using 2 capacitors (C11, C12) and the inductor L1 to about 50 ohm. The transistor has an output impedance match, (C13, C14, and L3) to get best performance for an 50-75 ohm antenna.

# The inductor L1 is made by a wire 2 turns with 5mm diameter.
# The inductor L2 is made by a wire 7-9 turns with 6.5mm diameter.
# The inductor L3 is made by a wire 4 turns with 6.5mm diameter.

L4 is a Axial Lead Bead, which reject RF very good and has low resistance. You can use almost any choke or large inductor for L4, it is not a critical component.
The FM transmitter require 2 AAA batteries and consume about 38mA.
To get rid of batteries, I have added a voltage regulator IC1, to the PCB which deliver 3.3V to the FM transmitter unit.

The PCB is mirrored because the printed side should be faced down the board during UV exposure.
To the right you will find a pic showing the assembly of all components on the same board.
This is how the real board should look when you are going to solder the components.
It is a board made for surface mounted components, so the copper is on the top layer.

Grey area is copper and each component is draw in different colours all to make it easy to identify for you.
The scale of the pdf is 1:1 and the picture at right is magnified with 4 times.
Click on the picture to enlarge it.

Remember that the case of the Q3 is the collector and has direct connection to +12V DC.
This case must NOT come in contact with the ground plane (GND) or any order parts of the PCB.
At the right photo below, you can see that I have soldered Q3, 3-5mm above the ground plane.

Preparing BCP for transistor Q3:
The picture below show a vertical cut through the PCB.
Here you can see the Top side which has the strip line connections to all the parts and to the transistor legs Base and Collector.
You can also see the ground plane on the other side of the PCB.
After I have drilled the thin hole for the transistor legs, I use second larger drill (3mm), and drill a little bit into the ground plane.

The larger 3mm drill remove the copper around the hole and you will have no electric contact between the ground plane and the legs of the transistor.
The procedure must be done for both the Base-leg and the Collector-leg. Since the Emitter-leg is already connected to ground, this hole doesn't need to be modified.
As you see of the picture below, the transistor leg is connected (soldered) to the pad, but the leg has no connection to the ground plane.

Soldering and testing:
The soldering of this unit is pretty basic.
Connect all parts and make sure you have no soldering bridges on the PCB. soldering wick and rosin are good tools to have handy while soldering.
When testing the amplifier I advice you to use a 50 ohm dummy resistor as load or a proper antenna (more info about antenna below).
Make sure you use a non-inductive resistor. Before you switch on power you should set the variable capacitors C13 to max capacitance and C14 to min capacitance.

DC testing:
To make sure that both transistors Q1 and Q2 has good working point I advice you to measure the DC voltage at the junction R1 - FB1 and R4 - FB2.
I measured with NO input RF signal:

DC volt FB1 = 3.7 to 3.9 V
DC Volt FB2 = 7.1 to 7.4 V

Now your unit is ready to be tuned for best performance!

Download : Project Documentation External Antenna

AM25 - Professional AM Transmitter Kit

type="html">Synthesized Professional Quality for your AM Station!

* Fully synthesized, no frequency drift!
* Ideal for schools
* Microprocessor controlled
* Strappable for higher power output where regulations permit
* Includes AC power adapter and case set

Run your own AM radio station!
The AM25 operates anywhere within the standard AM broadcast band, and is easily set to any clear channel in your area. The design is similar to that of a commercial radio transmitter, so you'll learn how the "big guys" operate. It is widely used by school - standard output is 100 mW, with range up to 1/4 mile, but is jumper setable for higher output where regulations allow. Broadcast frequency is easily set with dip-switches and is stable without drifting. The transmitter accepts line level input from CD players, tape decks, etc. Includes case & knob set & AC power supply.
Note: The AM25 is a do-it-yourself learning kit that you assemble. The end user is responsible for complying with all FCC rules & regulations within the US, or any regulations of their respective governing body.

Download AM25 Manual Kit Visit Page

AM1C - Entry Level AM Radio Transmitter Kit

type="html">#1 Scouting Project For Years

* Tunes entire 550 to 1600 KHz AM band
* Operates on 9 to 12 VDC, includes case set
* Standard line level input with RCA phono jack
* 100 mW output. Range up to 1/4 mile under optimum conditions

The AM1 is a great first kit, and a fine low power AM broadcaster for the hobbyist on a budget. It's a great way to learn the basics of AM broadcast technology, not to mention basic soldering and component identification (if you're a beginner!) The transmitter can be tuned to broadcast anywhere in the AM band (550 to 1600 kHz). Setting frequency is simple - tune a nearby AM radio to the desired frequency, then adjust the AM1 coil to match the radio. With 100 mW of output power, range can be up to 1/4 mile. The AM1 has been used by Scout camps, churches, schools, and other organizations to provide easy and low cost communications.

Note: The AM1C is a do-it-yourself learning kit that you assemble. The end user is responsible for complying with all FCC rules & regulations within the US, or any regulations of their respective governing body.

Download AM1C Manual
Visit Page

FM Transmitter With 9 Volt Battery

type="html">This new FM Transmitter Kit can transmit over 900 feet in the open depending on aerial used with 9 volt battery. The tank oscillator coil is built into the circuit board, and has been tinkered with to give the best distance and stability for it's size. The battery supply rails have been well tied together with respect to radio frequencies.

The tracks are also thicker making the fm transmitter circuit a single ‘solid’ block eliminating RF currents in different parts of the circuit. This also means the battery no longer has RF on it which makes the whole unit a lot more frequency stable. Can be tuned anywhere in FM band.

* L: 1-3/4" W: 7/8" H: 1/2"
* Requires 9 Volt Battery
* Transmission frequency is user selectable.
* Transmitter can be listened to on any FM radio.

Download kit manual for complete details, including schematic and theory of operation. Visit Page

Wide Band Synthesised FM Transmitter

type="html">Phase-Locked Loop (PLL) based crystal-locked wide band synthesised FM transmitter delivering a high quality, stable 10mW output. Accepts both MIC audio signal (10mV) and LINE input (1v p-p) for example hi-fi, CD, audio mixer (like kit 1052) or computer sound card.

The Radio Frequency (RF) output circuitry includes a three-pole filter for reduction of harmonics and other spurious signals. The spurious output signal level is better than -40dBc (0.0001 times the power of the wanted signal level), which makes the project suitable for driving an external power amplifier.

It delivers up to 10milliwatts of RF power to the antenna which can be a simple single wire about 74cm long (or open dipole or ground plane). Output power can be boosted to 250mW when used with our FM Power Amplifier.

Ideal project for the beginner who wants to get started in the fascinating world of FM broadcasting. See documentation link below for full details.

The transmitter is powered from a 12v supply, but it will operate from 9 Volts to 16 Volts. Please note that most standard DC mains adaptors are unsuitable for powering FM transmitters as they introduce an intolerable level of mains hum.

Download Manual 1 2 with Schematic and parts list. visit page

FM Telephone Transmitter

type="html">This miniature transmitter attaches in series to your telephone line, transmits the conversation to an FM receiver. Tune to a clear spot in the FM band of your radio. Completely parasitic; i.e. uses the power from the telephone line and needs no battery. The circuit might be used to share or record conversations, but not intended for illegal use.


* L: 1-3/4" W: 3/4" H: 1/2"
* Powered by phone line.
* Uses phone line for antenna.
* Transmission frequency is user selectable.
* Transmission can be listened to on any FM radio.
* Includes alligator clips for easy connection to phone line.

Download Manual for complete details, including schematic and theory of operation. Visit page.

Square Wave Oscillator 1Hz - 100KHz

type="html">A square wave generator is one of those pieces of equipment that has many uses in the workshop yet few hobbyists actually have. This simple kit, based on the popular 555 timer IC, generates six preset frequencies from 1Hz to 100khz. It has a wide operating voltage range and even provides visual indication of the output.

Easy-to-build kit generates six square waves of 1Hz, 10Hz, 100Hz, 1KHz, 10KHz & 100KHz output frequency using the onboard jumper selectors.

Ideal for the DIY test bench or school teaching project.

The kit is constructed on a single-sided printed circuit board (PCB). The PCB measures 78 x 50mm and will mount on a small Plastix “Jiffy” box. Protel Autotrax & Schematic were used to design the PCB.

Download User manual with schematic. Visit page.

Audio Frequency Function Generator 20Hz - 20KHz

type="html">This is an AF function generation covering the frequencies between 25-25,000 Hz in three bands. It has sine, square and triangular saw tooth outputs and has sufficient output to drive any amplifier and low distortion to be useful in high precision measurements.

Freq. response:... 25-25,000 Hz (three ranges A, B, C)
Range A:..25-250 Hz
Range B:..250-2500Hz
Range C:..2500-25,000 Hz
Distortion:..0.5 % (Max.)
Output voltage:..10 V pp Sine & Triangular
16 V pp Square wave
Output impedance:... 600 ohm

How it Works
The frequency generator uses an IC the TL082 which is a dual op-amp to produce the basic
waveforms. The first of the two op -amps in the IC is used as an oscillator the frequency of
which can be set by means of the potentiometer P2 and its range depends on the value of the
capacitor C3 and is selected by means of S1. The trimmer P1 is used to adjust the duty cycle
of the oscillator. The second op-amp is an integrator which converts the triangular wave form
that is produced by the oscillator to a square one. P4 is used to adjust the amplitude of the
signal. P3 is used to adjust the amplitude of the triangular waveform.

The signal from the output of the oscillator is taken to the circuit built around the two transistors to be converted from triangular to sinusoidal. The two trimmers P5 and P6 are used to adjust the shape of the positive and negative portions of the signal for the best symmetry a nd minimum distortion and P7 is the potentiometer which adjusts the output level for this waveform. As you see the circuit consists of fairly basic building blocks with independent adjustments for every one of them which makes a very versatile and easy to operate instrument. The power supply is also incorporated on the circuit board and you only have to connect 24 VAC across the rectifier bridge to make the circuit work.

Download User Manual
with schematic. Visit page.

High Gain TV Antenna Boosters

type="html">This is a small, broad band, signal Antenna boosters which covers the frequencies from 40 to 900 MHz. These frequencies include TV in VHF and UHF and also the radio broadcasting frequencies in the 88 - 108 MHz FM band. It is connected between the antenna and the input of your receiver and boosts the signals by up to 20 dB, thus making it possible to receive even the weakest signals.

Technical Specifications
Frequency range: 40-860 MHz
Signal gain: 15-22 dB
Input/output impedance: 75 Ohm
Working voltage: 9-18V DC
Power Supply: 9V battery
Board Dimensions: 41x55mm
Board Connections Solder Posts

How The Antenna Booster Works

The circuit is built around a single transistor a UHF low signal device, the BFW 92. This transistor can operate in frequencies as high as 1.6 GHz, and has a gain of 23 dB. The signal from the antenna is applied to the input of the circuit and through C5 is fed to the base of the transistor. It is amplified and from the collector of the BFW 92 through C2 and C1 is taken to the input of the radio or TV receiver.

The circuit operates off a small 9 V battery which, because of the very low power
consumption of the circuit, is going to last for a very long time.

Download User Manual with schematic. Visit page