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Simple and Budget DIY - How to Make An FM Transmitter?
Are you reluctant to buy FM radio broadcast transmitters because of the high price and not familiar with the working principle? Why not DIY a simple and practical FM radio broadcast transmitter or FM transmitter first? This tutorial will give you a detailed introduction on how to make and assemble an working FM broadcast transmitter, whether you are amateur or veteran, with only a few minutes reading and a little material cost, you could learn how to make and assemble a simple and practical FM radio broadcast transmitter. Additionally, this tutorial can not only improves your hands-on ability but also saves you expensive equipment purchase and maintenance costs. Get ready on it!
Anyone can buy an FM antenna and start their own radio station. All one needs is the right equipment and, of course an FCC license, which is not to terribly difficult to obtain. If you have ever dreamed of owning your own radio station, it is as easy as finding an FM broadcast equipment distributor that specializes in antenna sales for radio broadcasting. FMUSER can make your dream come true. We specialize in radio broadcasting equipment, and we even help our customers obtain their FCC license if needed. We can even help you build your radio station. We have the lowest prices on all of the equipment you need for your radio broadcast. Contact FMUSER today!
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If you're looking for how to make an long-ranged FM transmitter antenna, please kindly visit this tutorial:
How to DIY your FM Radio Antenna|Homemade FM Antenna Basics&Tutorials
1. Things You Should Know before Getting Started
2. Creating a simple FM radio broadcast transmitter
3. How to Make A 5KM Long-Ranged FM Transmitter?
4. How to Make A Low Powered FM Transmitter?
5. How to Make A Very Simple FM transmitter?
6. How to make A Simple IPOD FM Transmitter?
Best Budget Low-power FM Radio Broadcast Trasnsmitter in 2021
1. Things you should know before getting started
Also read: What is the Difference between AM and FM?
Name |
Sample Graph |
Functions |
The Power Supply |
|
Providing an electrical signal to operate the transmitter. |
The Oscillator |
|
Creating the alternating current, a carrier wave, that the transmitter sends through the antenna. |
The Modulator |
|
Adding information to the carrier wave. In the case of FM (frequency modulation), the modulator either slightly increases or decreases the frequency of the carrier wave. |
TheAmplifier |
|
Increasing the power of of the wave. More powerful amplifiers allow for a larger broadcast area. |
The Antenna |
|
Converting the amplified signal to radio waves. |
People often call antennas aerial. For FM radio stations, antennas generally refer to FM radio broadcast antennas. There are two types of such antennas. They are installed on the transmitting end (corresponding to FM radio broadcast transmitter) and the receiving end ( FM radio receiver) Although they are installed in different geographical locations, they are similar in terms of their working principles.
Also read: How to DIY your FM Radio Antenna|Homemade FM Antenna Basics&Tutorials
Both the antenna at the transmitting end and the antenna at the receiving end act on radio waves. The main function of the antenna at the transmitting end is to receive and transmit the electrical signals generated by the FM radio broadcast transmitter and transmit them, while the receiving end antenna is responsible for receiving these radio waves. wave. It is worth mentioning that these radio waves can travel a considerable distance (even can be transmitted to outer space). Therefore, if you want to receive these radio waves transmitted over a long distance, the receiver must be very powerful, otherwise it is easy Cause various problems, such as noise interference problems.
To create a simple radio transmitter, what you want to do is create a rapidly changing electric current in a wire. You can do that by rapidly connecting and disconnecting a battery, like this:
When you connect the battery, the voltage in the wire is 1.5 volts, and when you disconnect it, the voltage is zero volts.
By connecting and disconnecting a battery quickly, you create a square wave that fluctuates between 0 and 1.5 volts.
* A sine wave fluctuates smoothly between, for example, 10 volts and -10 volts.
Information transfer
If you have a sine wave and a transmitter that is transmitting the sine wave into space with an antenna, you have a radio station. The only problem is that the sine wave doesn't contain any information. You need to modulate the wave in some way to encode information on it. There are three common ways to modulate a sine wave:
Frequency Modulation - FM radio stations and hundreds of other wireless technologies (including the sound portion of a TV signal, cordless phones, cell phones, etc.) use frequency modulation. The advantage to FM is that it is largely immune to static. In FM, the transmitter's sine wave frequency changes very slightly based on the information signal.
3. How to Make A 5KM Long-Ranged FM Transmitter?
Here we are presenting a long range FM transmitter that can cover a reasonable distance of 5 kilometers / 3 miles and beyond with a one watt RF power with full circuit details, bill of material and testing procedure. With 12 volt DC it will deliver 1 watt RF power. With Yagi antenna, looking like early days of TV antenna with aluminum pipes at both at transmitter and receiver end looking each other at line of sight distance, the range can be up to 5 km / 3 miles.
This FM transmitter has 3 RF stages.
A (VFO) Variable frequency Oscillator (30 mw) ,
Q3 has to be 2N3866 with a heat sink for proper range. However 2N 2219 can be used that will but compromise the range drastically
Also read: What is Low Pass Filter and how to build a Low Pass Filter?
Testing:
Initially use a simple 75CM single wire standing straight as antenna for getting a range of about 100-200 meters indoor. Similar length telescopic antenna is also OK for testing which will give only about 100-200 meters range . But never go longer than 79 CM antenna wire thinking that it will cover higher range. In fact if you do so the range will fall.
Frequency of the transmitter can be set with in 88 to 108 MHz FM band by adjusting the TR1 (Trimmer 1) of the VFO or by changing the spacing between the Coil L1.
NOTE:Don't try to test the unit in evening to night because at that time many powerful FM stations will be active. Test it only at day time. A few people have had trouble with this circuit if not soldered properly. The biggest problem is not knowing if it is even oscillating, since the frequency is outside the range of most simple oscilloscopes. One may require the use of an RF frequency counter which is very expensive. So, to know that it oscillates, and just have to find out at what frequency , the simplest way is to put a cell phone having FM radio ( or any FM radio) in search mode near your transmitter to hear some sound while you tap the microphone. Please note very near the transmitter will have several frequencies responding to the microphone and one will get confused. So go ,at least 30 meters away from the transmitter after initial test as above is verified. There the display gives only one frequency to which it gets best clear sound and all other frequencies giving hissing sound and that is the frequency the transmitter is operating. Adjust the trimmer TR1a very very very (about 1 degree) little clockwise or anticlockwise ,the transmission frequency will change .Then put the cell phone to search again and find the frequency. If it is very near a powerful transmitter you will not get the range. Change the frequency again to go towards 106 MHz where no commercial transmission usually takes place.
Transmission range is adjusted by TR2. For that use a multi meter in 250 mA DC current mode in series with the 12 volt supply and then adjust the trimmer TR2 while the current is maximum. Adjust the current to around 75 mA (at 12 Volt DC supplied by a good adaptor) or the peak current by trimmer 2 to say about 85 mA. From the peak while you turn clockwise current will fall or while you turn anti clockwise it will also fall. And that is the best position of TR2 for full power delivery to the antenna. Please note Q3, round metal body must be fully covered by the black heatsink supplied, without which it will get badly heated up and finally get burnt. In around 100mA at 12 volt it shall cover a good range and shall be warm but beyond that current though it may cover a longer range it shall get very badly heated up ,and is likely to fail.Initially try to touch the heatsink and feel the heat as warm only. If it gets heated up badly switch off and reduce the current.
Important Note:
The output is fed to a coaxial cable (generally used for cable TV ) which is nearly matched to the Yagi antenna (though 300 Ohms) impedance of 75 ohms by trimmer TR 2 of the tuned circuit for maximum power delivery to the load ie the Yagi / GP antenna. Transmitter should never be powered without the antenna (ie the load) in which case the total power forms a SWR standing wave ratio on the power transistor Q3 heating it up badly to result in failure.
Also read: What is VSWR and how to measure VSWR?
Notes
1. It is advisable to engage any electronics technician for soldering if one has no prior professional experience in soldering and component identifying. Any excess heating more than 2 seconds may damage the component. Use only 25 watt soldering iron. Placing right value of resistor is most important. Read the colors carefully to ascertain its value. If a multimeter is available , then better measure it in ohms / Kohms range. It may not give exact value. Plus or minus 10% is acceptable. Reading disk ceramic capacitors need expertise. Place them correctly. Please refer the image.
Here is the schematic, PC board pattern, and parts placement for a low powered FM transmitter. The range of the transmitter when running at 9V is about 300 feet. Running it from 12V increases the range to about 400 feet. This transmitter should not be used as a room or telephone bug.
|
|||
Schematic |
PC Board Layout and Parts Placement |
||
Part |
Total Qty |
Description |
Substitutions |
C1 |
1 |
0.001uf Disc Capacitor |
|
C2 |
1 |
5.6pf Disc Capacitor |
|
C3,C4 |
2 |
10uf Electrolytic Capacitor |
|
C5 |
1 |
C5 1 3-18pf Adjustable Cap |
|
R1 |
1 |
270 Ohm 1/8W Resistor |
270 Ohm 1/4W Resistor |
R2,R5,R6 |
3 |
4.7k 1/8W Resistor |
4.7K 1/4W Resistor |
R3 |
1 |
10k 1/8W Resistor |
10K 1/4W Resistor |
R4 |
1 |
100k 1/8W Resistor |
100K 1/4W Resistor |
Q1, Q2 |
2 |
2N2222A NPN Transistor |
2N3904, NTE123A |
L1, L2 |
2 |
5 Turn Air Core Coil |
|
MIC |
1 |
Electret Microphone |
|
MISC |
1 |
9V Battery Snap, PC Board, Wire For Antenna |
|
5. How to Make A Very Simple FM transmitter?
This sample test shows you how to build a very simple FM transmitter from thirteen components, a Printed Circuit Board (PCB) and a 9v battery. This project was designed to be mounted on a PCB, however you don’t have to. You could construct the project on Vero board (strip board) or any other 0.1” pitch style of project board. If you just want to experiment with this circuit, you don’t even need a board; you can just solder the component s together and let the completed project just rest on the work top. No matter which style you choose, try to keep all component leads nice and short. You could also make the PCB much smaller than the one shown here which is approx. 3 cm square. This is a good size to keep the unit small but nicer to work on for beginners. If you wanted to make one really small, you could use all SMT parts.
Also read: How to Eliminate Noise on AM and FM Receiver?
The value of capacitor C5 controls the transmission frequency range.
These are only approximate as frequency is determined by the L1 and the specification of the transistors, but these ranges were observed in the prototype unit. Also note that the closer the coil windings are, the lower the frequency will be. Just slightly compressing the coil dropped the transmission frequency by over 1 MHz.
The first think to do is wind and mount the coil. The coil is simply a length of 0.6mm / 22swg copper wire wound into a coil. Take a 10cm length of bare copper wire and wind it around a suitable former; the blade of a jewellers screwdriver or knitting needle is ideal.
Once the coil has been wound, leave it on the winding former for now so that it doesn’t get deformed whilst your mounting it. Pop each end of the coil into the correct PCB hole stretching the coil as needed so that its windings are evenly spaced. Turn over the PCB and solder in both ends of the coil.
Next mount the remaining components except the transistors, in any order that you feel most comfortable with.
When it comes time to solder on the microphone you need to be carfull. On the base of the mic there will be two solder pads. If you look closely, one of the pads should be connected to the case; this is the Negative.
You don’t need anything clever in the way of aerials for this transmitter. The longer the aerial wire is, the further the transmission range will be but for testing, just connect a 25cm length.
Ok, now for the tricky bit. Assuming you’ve connected everything together correctly, then depending on the transistors used, tolerance of the components, characteristics of your coil and position of the trimmer capacitor, when you connect the battery you will be transmitting audio somewhere on the FM band, probably between 80MHz and 150MHz.
Crushed coil to lower the frequency
Reducing the value of R4 will increase the drive to Q2 thus increasing the transmitter power output. However, if you reduce R4 too much you will shorten the life of the battery and may eventually destroy transistor Q2.
Components | Decription | Comments |
R1 |
2.2K 5% |
|
R2 | 1.2K 5% |
|
R3 | 100K 5% |
|
R4 | 560 ohms 5% |
|
C1 | 1UF |
|
C2 | 22PF |
|
C3 | 4.7NF |
|
C4 | 20PF Varcap |
|
C5 | 5.6PF | See text on picking a suitable value |
Q1 | Gen NPN | Or just about any small NPN transistor |
Q2 | Gen. NPN | Or just about any small NPN transistor |
MC1 | Elect. Mic |
|
L1 | See Text |
|
A1 | See Text |
|
BT1 | 9V Battery clip |
|
Also read: What is QAM: quadrature amplitude modulation
6. How to make A Simple IPOD FM Transmitter?
Things used in this project
1. TI SN74LS138N - 4 Input NAND gate Schmitt Trigger
Thanks to the approach given by Tony Van Roon tuning this FM Transmitter circuit is very easy compared to other circuits since it does not have an Inductor or a trimmer. To start with simply power on the circuit and connect the speaker to the circuit as shown in the circuit above. Now connect the iPod or any audio device to the 3.5 mm jack and play the music. You should be able to hear your audio through the speaker. If not the problem should be with your LM386 connections. If the audio can be heard, disconnect the speaker and proceed with the tuning process.
Use a Radio with tuner and start turning your knob to know at which frequency you oscillator is broadcasting. The best way is to check around 100 MHz as it would most likely work around this frequency. Keep your volume at your maximum and tune slowly till you can hear the song that is being played through your audio source.
1. If you hear a strange noise at a particular frequency and want to find to if this is your oscillator frequency. Simply turn off the circuit and turn in again, your radio should produce a crackling noise if the frequency is correct
2. Extend the antenna of your radio to its full length and place it close to the circuit initially
3. Change the operating voltage within 4.5 to 5 V to change the frequency at which you are broadcasting because sometimes your frequency might have clashed with another popular FM band.
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