The following posts explains how to build a simple to build FM stereo transmitter circuit using IC BA1404.
About the IC BA1404
An exceptional stereo audio FM wireless transmitter circuit is presented below.
The circuit relies upon the IC BA1404 from ROHM Semiconductors.
BA1404 is a monolithic FM stereo modulator which includes integrated stereo modulator, FM modulator, RF amplifier circuitry.
The FM modulator could be controlled from 76 to 108MHz and power source for the circuit could be nearly anything between one.25 to three volts.
Circuit Description
In the circuit R7, C16, C14 and R6, C15, C13 makes the pre-emphasis system for the right and left stations respectively.
This is achieved for complementing the frequency response of the FM transmitter with the FM receiver.
Inductor L1 and capacitor C5 is employed to fix the oscillator frequency. Group C9,C10, R4,R5 enhances the station splitting up.
38kHz crystal X1 is linked between pins 5 and 6 of the IC. Composite stereo reception is formed by the stereo modulator circuit employing the 38kHz quartz regulated frequency.
Construct the circuit on a high quality PCB.
Operating the circuit from a battery pack minimizes disturbances.
Work with an 80 cm copper cable as antenna.
For L1 try to make three turns of 0.5mm dia enamelled copper wire on a 5mm dia ferrite core.
Stereo FM Transmitter Circuit Diagram
Solomon says
Hello Sir, I Like This Circuit, And I Want To Construct It, But I Have Some Questions To Ask
1. For Instance If I Dont Get 38khz Crystal Oscillator, Can I Generate 38khz From 555 Timer And Feed It To The Circuit? And Can It Work Normal Like For Crystal Oscillator?
2. Can It Be Modified By Adding Press Botton For Scanning Or Selecting The Frequency?
3. Can We Add A Power Indicator Led To It?
4. Can It Be Modified By Adding Sound Indicator Circuit To It?
Swag says
Solomon, we use crystal to ensure extremely stable frequency which cannot be achieved using ICs like 555, so it might not work.
You may have to refer the datasheet of the IC to learn if any modifications may be possible or not externally.
Music level indicator can be added at the output side of the circuit
Sunirnay Chatterjee says
i made a BA1404 Stereo FM Transmitter but unable to found stereo FM receiver circuit . Please help me as soon as possible.
Swag says
you can use your mobile phone’s FM radio…
Carlo Cruz says
Can I connect this circuit to the TV output Audio RCA connectors
Swagatam says
it's for radio FM range….won't work for TV I guess…
Carlo Cruz says
Hello i got this IC but I used a different circuit and its not working out as expected in the first place how do I know the value of the frequency that is being transmitted?
Swagatam says
Hello, It would be difficult for me to troubleshot without practically checking it…
you can check the frequency by capturing the transmission on any standard FM radio and then checking the frequency level on the tuning calibration of the radio.
utkarsh verma says
though i would suggest creating an LCR meter using arduino..It is an easy build and helps to find transmission frequency.
Carlo Cruz says
What is the software for doing the simulation BA1404?
utkarsh verma says
Checked it…The datasheet didn't help much….
Swagatam says
try a longer antenna.
utkarsh verma says
Currently using a 1.5m long one.
Swagatam says
that's quite long and sufficient…not sure, there could some other hidden issue somewhere
Swagatam says
OK, good, thanks for updating the info
utkarsh verma says
Made this as you instructed….still not getting a clear reception and the audio transmission isn't recognizable. What should I do?
Swagatam says
check the datasheet of the IC and see if there's any refinements to be done.
utkarsh verma says
You said 5 turns initially, if I don't get correct transmission, should I increase or decrease the number of turns?
Swagatam says
you will have to experiment with the turns because the original IC datasheet has not informed about the exact number of turns for the coil
utkarsh verma says
ok……
utkarsh verma says
Wait then i'm sending the link to ground fill pcb pdf and the silkscreen too….
This is the link to the shared folder on google drive:
https://drive.google.com/drive/folders/0B-5jjw-tjYplaGJuVjN5cGUxOWc?usp=sharing
Swagatam says
yes that looks OK to me.
utkarsh verma says
I have neither a ferrite core nor a variable inductor. Please post a way to use a static inductor with a 2-18pf variable capacitor.
Swagatam says
…ferrite cored inductor is a must for the explained design
utkarsh verma says
ok…made this circuit…but getting too much static. What do you think is the culprit?
utkarsh verma says
Wait. I just found a 5mm ferrite core. But since I don't have 0.5mm copper wire. Would you please tell me the improvised version of this coil for SWG22 wire. I can make air core coils according to given values but I don't know how ferrite cores change the inductance value so please tell me how to make a coil with 5mm ferrite core using SWG22..Hope this will eliminate the static caused by my circuit.
utkarsh verma says
Please tell me how make this inductor for 22SWG as 0.5mm copper wire isn't available in my city. SWG22 is 0.711mm wide. I have salvaged a 5mm ferrite core. How many turns should I make to use it as an inductor in this circuit?
Swagatam says
0.5mm is not critical you can use any other gauge thicker than that….
use 5 turns initially
Swagatam says
to prevent noise use PCB with grounded tracks
Swagatam says
yes it must be ground filled type or "copper pour" type PCB to enahnce stability.
sorry I cannot check your PCB if it's posted in some other electronic website.
you can post in some free image hosting site, and send the link here
dairo oluwadamilare says
Can this circuit transmit up to 2km? I also want to design mobile Phone call jammer can u pls upload the circuit or show me the link to mobile call jammer circuit. Thanks
utkarsh verma says
is crystal resonator necessary??
Rushi Palkar says
how to adjust frequency???
Swagatam says
by altering C6
Anonymous says
Thanks for this circuit, u are simply the best. Pls i don't really understand where to get the 38kHz crystal. Pls tell if there is any other name for the 38kHz so that i can tell them when i go in search of it in electronic/electrical shops for easier understanding.
Swagatam says
Thanks so much, please view these pic, the device looks like this:
http://radiohobbystore.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/3/8/38khz-crystal-stereo-coder.jpg
http://store.rf-modules.com/product.php?id_product=93
Rajib.digi says
At First Thanks for this Circuit,
Where the switch position by which The FM modulator could be controlled from 76 to 108MHz.
Rajib
Swagatam says
thanks! there's no switch for it, L1 and C5 can be adjusted for transmitting the required frequency