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 še danes!

Delitev je skrb!

If you're looking for how to make an long-ranged FM transmitter antenna, please kindly visit this tutorial:

Kako narediti svojo FM radijsko anteno ｜ Osnove in vaje o domačih FM antenah

vsebina

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

>>Poizvedi zdaj

1. Things you should know before getting started

Kaj je frekvenca modulacije (FM)?

Frequency modulation is a technique or a process of encoding information on a particular signal (analogue or digital) by varying the carrier wave frequency in accordance with the frequency of the modulating signal. As we know, a modulating signal is nothing but information or message that has to be transmitted after being converted into an electronic signal...>> Več

Preberite tudi: Kakšna je razlika med AM in FM?

How Does an FM Transmitter Work?

FM radio broadcast transmitter is one of the most important equipment required in radio broadcasting. Its function is to obtain sound and broadcast the sound to various receivers in a certain area through an antenna (the coverage of the broadcasting area is affected by many factors, Such as the installation position of the transmitting antenna, the weather or the power of the FM radio broadcast transmitter, etc.)

The process of transmitting sound information (radio broadcasting) seems simple, but in fact it is the result of the coordination of different components in the FM radio broadcast transmitter

The following are typical FM radio broadcast transmitter working components and their working principles:

Ime	Sample Graph	funkcije
Napajanje		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.
Antena		Converting the amplified signal to radio waves.

Kako deluje antena FM?

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.

Preberite tudi: Kako narediti svojo FM radijsko anteno ｜ Osnove in vaje o domačih FM antenah

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.

In practical applications, the broadcast information (such as various songs, commercials, etc.) that we receive through various devices, such as radios, is actually the radio wave signal sent by the broadcast station on the transmitting end.

After the broadcasting station records the information that needs to be broadcast through a certain device (this equipment is usually a microphone), the FM radio broadcast transmitter will convert the broadcast information into electrical energy, and then the electrical energy of the broadcast information will continue to surge through the FM antenna, and the Increase the signal strength or increase the power during the surge. During this period, the electrons in the electric current that surge back and forth across the length of the antenna to create electromagnetic radiation (radio waves), and will transmit data at the speed of light, and then These radio waves will be captured by the antennas of other receivers and converted, and finally the radio wave signals are converted from electric current into sound and data to be received by the listener.

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2. Creating a simple FM radio broadcast transmitter

FMUSER explained in detail the definition of FM, the working principle of FM radio transmitter and FM receiver in the first part. In this part, FMUSER will provide several methods for making simple FM transmitters for your reference.

Make your own FM transmitter

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 better way is to create a continuously varying electric current in a wire. The simplest (and smoothest) form of a continuously varying wave is a sine wave like the one shown below:

* A sine wave fluctuates smoothly between, for example, 10 volts and -10 volts.

By creating a sine wave and running it through a wire, you create a simple radio transmitter. It is extremely easy to create a sine wave with just a few electronic components -- a capacitor and an inductor can create the sine wave, and a couple of transistors can amplify the wave into a powerful signal. By sending that signal to an antenna, you can transmit the sine wave into space.

Preberite tudi: Najboljših 9 najboljših oddajnikov radijskih oddajnikov, dobaviteljev in proizvajalcev s Kitajske / ZDA / Evrope v letu 2021

Prenos informacij

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:

Pulse Modulation - In PM, you simply turn the sine wave on and off. This is an easy way to send Morse code. PM is not that common, but one good example of it is the radio system that sends signals to radio-controlled clocks in the United States. One PM transmitter is able to cover the entire United States!

Amplitude Modulation - Both AM radio stations and the picture part of a TV signal use amplitude modulation to encode information. In amplitude modulation, the amplitude of the sine wave (its peak-to-peak voltage) changes. So, for example, the sine wave produced by a person's voice is overlaid onto the transmitter's sine wave to vary its amplitude.

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.

Once you modulate a sine wave with information, you can transmit the information!

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3. How to Make A 5KM Long-Ranged FM Transmitter?

Tukaj predstavljamo FM oddajnik dolgega dosega, ki lahko pokriva razumno razdaljo 5 kilometrov / 3 milj in več z enojno vatno RF močjo s podrobnostmi polnega kroga, materialom in postopkom testiranja. Z 12 voltom DC bo dobil 1 watt RF moč. Z Yagi anteno, ki je videti kot zgodnje dni TV antene z aluminijastimi cevmi na obeh oddajnikih in sprejemnikih, ki gledata drug na drugega na liniji pogleda, je lahko območje do 5 km / 3 milj.

Ta FM oddajnik ima stopnje 3 RF.

A (VFO) Oscilator spremenljive frekvence (30 mw),

Stopnja gonilnika razreda C (150 mw) kot medpomnilnik in

Končni RF ojačevalnik moči razreda C (1 Watt)

V bistvu mora vsak FM oddajnik imeti napetostno kontroliran oscilator (VCO). To je visokofrekvenčni oscilator, katerega izhodna frekvenca se spreminja glede na napetost, uporabljeno na določeni kontrolni točki. To je oscilator s spremenljivo frekvenco (VFO). Q1 s pripadajočimi komponentami iz VFO. Izhod VFO se prenese na Q2. Q2 kot vmesni pomnilnik ne nalaga VFO, temveč samo ojača moč. Ta izhod se napaja v končni RF ojačevalnik moči Q3, katerega izhod napaja uglašeno vezje. Na oskrbovalni progi se uporablja več kondenzatorjev C 4,8,9,10 za HF filtracijo. Če se transmistor VFO Q1 neposredno napaja z mikrofonom na svoji bazi, postane vezje FM oddajnika.

Paket Q2 mora biti tipa "TO 92-B" (nekoliko večji od paketa BC547) in ne preprost za 92, ki je nekoliko manjši (enako kot paket BC547). Poleg tega upoštevajte, da so konfiguracije pinov za te vrste 2 različne. V primeru, da je uporabljen paket TO92, povečajte vrednost R7 na 56 ohms 1 / 2 watt, ki ne bo vžgala. Toda ta paket TO92 lahko vpliva na obseg

Q3 mora biti 2N3866 s hladilnikom za ustrezno območje. Vendar pa je mogoče uporabiti 2N 2219, ki bo drastično ogrozil razpon

Preberite tudi: Kaj je nizkoprepustni filter in kako zgraditi nizkoprepustni filter?

Testiranje:

Najprej uporabite preprosto enojno žico 75CM, ki stoji ravno kot antena, da dobite vrsto merilnikov 100-200 v zaprtih prostorih. Teleskopska antena podobne dolžine je prav tako primerna za testiranje, kar bo dalo le približno merilno območje 100-200. Ampak nikoli ne gredo dlje kot 79 CM antene žice misli, da bo pokrival višji razpon. V bistvu, če boste to storili, bo obseg padel.

Frekvenco oddajnika lahko nastavite s frekvenčnim pasom 88 na 108 MHz, tako da prilagodite TR1 (Trimmer 1) VFO ali spremenite razmik med tuljavo L1.

Prilagoditev frekvence:

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.

The distance adjustment, after connecting a Yagi or GP antenna:

Območje prenosa se prilagodi s TR2. Za to uporabite več merilnikov v enosmernem načinu 250 mA v seriji z napajanjem 12 in nastavite trimer TR2, medtem ko je tok največji. Prilagodite tok okoli 75 mA (pri 12 Volt DC, ki ga napaja dober adapter) ali maksimalni tok s trimerjem 2 in povejte o 85 mA. Od vrha, medtem ko obračate v smeri urinega kazalca, bo tok padel ali pa, ko se obračate proti smeri urinega kazalca, bo tudi padel. In to je najboljši položaj TR2-a za popolno napajanje antene. Prosimo, upoštevajte Q3, okroglo kovinsko ohišje mora biti popolnoma pokrito s črnim hladilnikom, brez katerega se bo slabo segrevalo in končno sežgalo. V okrog 100mA na 12 volt mora pokrivati dober razpon in biti topel, vendar onkraj tega trenutnega, čeprav lahko pokriva daljše območje, se mora zelo slabo segreti in verjetno ne bo uspel. ogrejte samo kot toplo. Če se segreje slabo se izklopi in zmanjša tok.

Pomembno opozorilo:

(Ne uporabljajte kovinskega izvijača. Za uporabo kot izvijač morate uporabiti majhen kovinski kovinski predmet, ki ne uporablja železa - to ne bo spremenilo frekvence, ko boste roko obrnili blizu ali stran od obrezovalnika, ki se običajno dogaja v kovinski Vmesnik ali aluminijasti izvijač z izoliranim vrhom.

Za dolge razdalje uporabljajte Yagi anteno

Izhod se napaja na koaksialni kabel (ki se običajno uporablja za kabelsko televizijo), ki je skoraj usklajen z anteno Yagi (čeprav je 300 ohm) impedanca 75 ohmov s trimerjem TR 2 nastavljenega vezja za največjo moč dobave tovora, tj. / GP antena. Oddajnika ne smete nikoli napajati brez antene (tj. Obremenitve), v tem primeru skupna moč ustvari razmerje stoječih valov SWR na močnostnem tranzistorju Q3, ki ga močno segreje, da povzroči okvaro.

Preberite tudi: Kaj je VSWR in kako izmeriti VSWR?

Opombe

1. Priporočljivo je, da za spajkanje vključite katerega koli elektronika, če nimate predhodnih strokovnih izkušenj s spajkanjem in identifikacijo komponent. Prekomerno ogrevanje, ki traja več kot 2 sekund, lahko poškoduje komponento. Uporabljajte samo spajkalnik 25 watt. Najpomembnejše je dajanje prave vrednosti upora. Previdno preberite barve, da ugotovite njeno vrednost. Če je na voljo multimeter, ga bolje izmerite v ohmih / Kohms območju. Ne sme dati točne vrednosti. Plus ali minus 10% je sprejemljivo. Za branje diskovnih keramičnih kondenzatorjev je potrebno strokovno znanje. Postavite jih pravilno. Oglejte si sliko.

2. Nekatere sestavine so se na svojih nogah nakopičile zaradi oksidacije zaradi shranjevanja. Pred spajanjem jih morate temeljito očistiti, da odstranite umazanijo z nožem. Kovinski tranzistor kot primer, kot je viden v paketu. Bolje očistite vse sestavne dele, tudi če na njih ni umazanije.

3. Če zatiči trimerja ne gredo v luknje, poskusite rahlo narediti luknje na tiskanem vezju večje s kakšno ostro iglo.

4. Pred montažo na tiskano vezje montirajte črni hladilnik na kovinski tranzistor.

5. Spajka odrežemo kos uporovnih nog na mikrofon in jih spajamo na PCB s pravilno polarnostjo. Telo je -ve.

6. Noge tranzistorjev vzdržujte najmanj 5 mm nad tiskanim vezjem in vse uporovne noge in tuljave v položaju spanja čim bližje tiskani plošči. Kondenzatorji kot običajno stojijo, vendar noge prilepite čim krajše na ploščo.

7. Tuljave so super emajlirane. Ne bodite pod vtisom, da so baker. Njihove konice je treba temeljito očistiti, da se emajl z nožem pred spajanjem odstrani.

8. Mora sprejeti prisluškovanje iz tuljave ne 1, po 1 zavoj s praskanjem z nožem emajla na točki in nato uporabite vsak kos kosov bakrene žice upora (ne železne žice) za spajkanje in priključite konec žice na luknjo na PCB.

9. L3 in L4 morata biti med seboj 90 stopinj.

10. Čiščenje umazanije in rje na nogah, kot je bilo pojasnjeno, je zelo pomembno. Vsi tehniki to vedo. Začetnik mora to razumeti. V nasprotnem primeru te komponente nikoli ne ujamejo.

11. Lahko uporabi baterijo 9 volta tako, da spajkamo rdečo do + ve in črno do -ve. Za uporabo na 12 volt DC vtičnica je 3 zatiči. Center pin je 12v + in drugi 2 zatiči so za 12 volt-ve. Enako povežite z majhnimi kosi žice. Red +, Black -ve do DC vtičnice.

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4. How to Make A Low Powered FM Transmitter?

Tukaj je shema, PC vzorec krovu, in postavitev delov za nizko powered FM oddajnik. Razpon oddajnika, ko teče na 9V je približno 300 metrov. To poteka od 12V povečuje obseg približno 400 noge. Ta oddajnik se ne sme uporabljati kot sobe ali telefonsko bug.


shematski		PC Board Postavitev in deli umestitev
Del	Total Qty	Opis	Zamenjave
C1	1	0.001uf Disc Capacitor
C2	1	5.6pf Disc Capacitor
C3, C4	2	10uf elektrolitski kondenzator
C5	1	C5 1 3-18pf Adjustable Cap
R1	1	270 1 Ohm / 8W upor	270 1 Ohm / 4W upor
R2, R5, R6	3	4.7k 1 / 8W upor	4.7K 1 / 4W upor
R3	1	10k 1 / 8W upor	10K 1 / 4W upor
R4	1	100k 1 / 8W upor	100K 1 / 4W upor
Q1, Q2	2	2N2222A NPN Transistor	2N3904, NTE123A
L1, L2	2	5 Turn Air temeljnega Coil
MIC	1	Electret mikrofon
MISC	1	9V baterije Snap, PC Board, žice za anteno

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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.

Preberite tudi: Kako odpraviti hrup na AM in FM sprejemniku?

Selecting the operating frequency range

The value of capacitor C5 controls the transmission frequency range.

In the UK, domestic FM radio receivers cover from around 88 - 108MHz.

The following table shows an approximate frequency range that can be expected for different values of C5.

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.

C5 Value Lower Freq. Upper Freq.

5pf 130MHz 180MHz

10pf 115MHz 152MHz

22pf 106MHz 124MHz

47pf 89MHz 97MHz

100pf 73MHz 75MHz

Note:Different makes of capacitors will give different frequencies.

I personally picked a frequency that was outside of domestic FM receives so that I wouldn't bother anybody; and nobody else can "tune-in" by accident. However, if you don't have a communications receiver then you will have to pick a frequency range that you can receive with your FM radio equipment.

Winding the coil

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.

You will need between 4 to 6 turns and you may have to experiment here. 6 turns gave my prototype a transmission frequency of around 120MHz. A coil with fewer turns should reduce the frequency.

Mounting the coil on the board

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.

The above three images show how the coil centre-tap wire is made and then fixed to the coil.

Solder the centre-tap wire to the approximate centre position of the coil. When it’s secure, turn over the PCB and solder the wire to the track and trim off the excess wire.

Solder the remaining components

Next mount the remaining components except the transistors, in any order that you feel most comfortable with.

Lastly, you need to mount the transistors Q1 & Q2, and you need to be VERY carful that you insert them the correct way. Depending on which transistors you use, you may have to bend some of the legs around each other. If you need to do this, make sure that they don’t touch each other.

Now solder in the wires from the 9 volt battery clip making sure you get the positive and negative the correct way around.

Connecting the microphone

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.

If you connect the mic the wrong way around it won't work and you will probably damage it.

Notice above C1 in figure 6, there is a small link wire - LNK.

This allows power to be applied to the microphone via R1. If you decide to not use this type of mic or to connect the transmitter to another audio source, you should remove this link.

Completed FM transmitter

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.

Make sure that the other end of the aerial doesn’t come into contact with anything; that includes any part of the circuit or anything that may be earthed.

When you’re done, you should end up with something that looks like the picture on the left.

First tests FM receiver showing 119.9 MHz

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.

Place your FM transmitter near an FM radio and SLOWLY start to tune from one end of the band to the other. As you tune the radio with one hand, keep gently tapping the microphone on the transmitter with the other hand. At some point you should hopefully start to hear the tapping. When tuning you need to experiment to find the exact frequency. When you find the frequency, make a note of it and keep going a bit further. Sometimes you can find a stronger signal a little further down the dial.

Those using a communications receiver or scanner should select WFM or Wide FM if available.

Changing the transmission frequency

Crushed coil to lower the frequency

With the component values specified, both my trial units popped up at around the same frequency.

I then “crushed” the coil slightly; almost certainly one or more of the turns are now shorting together (see fig.10) and this immediatly lowered the transmission frequency.

Frequency has dropped to around 110.9 MHz

When tuning the transmitter don't touch any part of the circuit as you will cause the output frequency to drift around.

Now the microphone used has a built in audio amplifier (see Figure 7) and I kid you not, it can hear an ant blowing its nose at 50 meters. If you just speak softly close up into the microphone it will probably sound distorted because you will over load the input.

The PCB was designed using DipTrace PCB software and there is a free version of this product available for download that can be used to modify / print the foil. You will find the original PCB foil for download at the end of this article.

One question this is often asked is "what's the transmission range?".

The problem with attempting to answer this question is that it depends on so many external factors including, number and density of obstacles between the transmitter and receiver, sensitivity of the receiver, the quantity and strength of other transmissions on or around the chosen wavelength that can overload the receiver, and the size of transmitting and receiving aerials. As a rough guide, assuming that a clear part of the frequency spectrum can be located and a nice long aerial is connected to the receiver, I've had around 250 meters in the city or built up area with a one Meter wire aerial on the transmitter, but a fair bit more distance out in the open of it it's used up high.

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.

Sestavni deli	Razkritje	Komentarji
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

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Preberite tudi: Kaj je QAM: kvadraturna amplitudna modulacija

6. How to make A Simple IPOD FM Transmitter?

Things used in this project

Hardware components

1. TI SN74LS138N - 4 Input NAND gate Schmitt Trigger

2. LM386 –Audio Amplifier

3. LM7805

4. Speaker-For testing puposes!

5. Capacitors

Naslednji diagram vezja prikazuje vezje oddajnika FM in potrebne električne in elektronske komponente za to vezje je napajanje 9V, upor, kondenzator, trimmer kondenzator, induktor, mikrofon, oddajnik in antena. Upoštevajmo mikrofon, da razumemo zvočne signale, znotraj mikrofona pa je prisotna kapacitivna tipala. Proizvaja se od vibracij do spremembe zračnega tlaka in izmeničnega signala.

In our circuit, the Audio Signal is given by a phone or IPod instead of a microphone. The Pre-Amplification is done using the LM386 Audio Amplifier IC. The 74LS138 along with 22pf capacitor acts as a Tank circuit which produces a strong carrier frequency and modulate it with our amplified audio signal like the 0.1 uH inductor. We do not have a RF-Amplifier in our circuit, but it can be added if you need to achieve a higher range.

it can be built on a breadboard or soldered to a Perf board. The complete circuit can be powered using a 9 V Battery. If you are using an adaptor to power it make sure you add filter capacitor to reduce the noise from switching. The circuit uses an LM386 Audio amplifier which acts as an Pre-Amplifier, this IC amplified the audio signals from the audio device and feeds it to the Oscillating circuit.

The Oscillating circuit should have an Inductor and a Capacitor. In our project the IC 74LS13 which is a 4-Input NAND gate Schmitt Trigger is designed to oscillate at 3rd order Harmonics which is around 100 MHz. A filter capacitor across the power rails of the IC is very important to make it working.

The 3.5 mm Audio Jack has three terminals in which are for channel L, channel R and Ground. We short the channel pins so that it becomes mono channel as shown in picture below and connect it to pin 3 and ground is connected to pin 2 of LM386.

Tuning into right frequency

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.

You Can Try the Following if You Hit A Wall

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.

4. (Totally optional) If you have a variable capacitor of range 0-22 pf you can replace the 22 pf cap with this trimmer and try changing its values.

Once you find out at which frequency you are working you can position the antenna in the right direction and enjoy your broadcasted music. Hope you got the project working.

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