Instructables
Picture of Hacking  FM Transmitter
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In this instructable i am going to shed light on a FM transmitter i had purchased from ebay a month ago. After purchasing this gadget i was happy for a couple of days until i found out that there was some discrepancy in this gadget. Firstly i found out that the Gadget was powered by AAA batteries which didn't lasted longer. Secondly most important the range that it was covering was very much shameful. Like about 100 feet in open space and if you were inside a building about 50 feet. Therefore i thought of doing something. After some research and gaining some inputs from Google. I found out that no such description were given for the particular model, as it was a Chinese made. 
But indeed i got some information about the gadget. Therefore i would like to share with Instructable.

My primary Objectives would be as Follows:-

1. The power source should be compromised.
2. It should be capable of adapting with both the adapter as well as with the batteries.

3. The ease of access should be incorporated like it should have the ability to get along with any of the multimedia device.
4. Could be carried along while travelling.
5. Finally the most important objective, the range should well be increased to about more than the regular given specification.
 
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ivmilicevic10 days ago
Is it possible to add line output to cheap fm transmitter, to use as mp3 player in DIY amplifier?
achaudhury992 months ago

I have a FM Transmitter Zebronics Vivo which uses a KST-6705T board. I have added its image. There are similar products from other brands which I feel may use same board. Links to these products from ebay follows. There are some nice videos in youtube which shows how to use them. Links follows. Its transmitter
Frequency is FM86MHZ.

Is it possible to increase the transmission range of this transmitter. Is it possible to change the transmitter frequency to some other for eg. 89MHz, so that I can tune my mobile phone to 89MHz and receive the signal transmitted from this transmitter.

5 in 1 Wireless Headphone

KST-670B-2 (MH2001)

http://lihigh.en.made-in-china.com/product/gMyQjNFJQsVX/China-5-in-1-Wireless-Headphone-KST-670B-2-MH2001-.html

Zebronics Vivo Wireless Headphone:

http://www.snapdeal.com/product/zebronics-vivo-wireless-headphone-fm/569973818?utm_source=earth_feed&utm_campaign=12_851&utm_medium=10183600

Zebronics Airwalk Diamond Series Headphone

http://www.amazon.in/Zebronics-Airwalk-Diamond-Series-Headphone/dp/B009Z7F8Y2?tag=googinhydr18418-21

Intex Wireless Roaming Over-Ear Headphone

http://www.amazon.in/Intex-Wireless-Roaming-Over-Ear-Headphone/dp/B00D6EG7FO?tag=googinhydr18418-21

You tube How to use videos:

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CDsQtwIwAA&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DgZK_4swXWRU&ei=K0P8U9GVGoHJuASmwYGIBw&usg=AFQjCNG163iYbZYk7lUhxzqACRgkZpZ0TA

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0CEEQtwIwAQ&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DOieDRaL9sfY&ei=K0P8U9GVGoHJuASmwYGIBw&usg=AFQjCNGBiv6YiriPoy8_aWdBeOycsLfVkg

Circuit Front.jpgProduct.jpgCircuit Back.jpg
ilovemoarK2 months ago

It killed mine (or I did not assemble properly) but this is very smart and creative!

samander8 months ago
Raikut, what is the range of this hack? Thanks in advance.
123mohan1 year ago
http://www.fmuser.org/

please visit this link.....for low power FM transmitter .... you love it..

mohan
Hi,

I have one similiar. I 've found that if you have a 35mm jack extension the signal improves with less interference. Save opening one up.
raikut (author)  microsurfer1 year ago
The range may extend if you add an extension as the wire itself will act as an antenna, but you would not get enough range as predicted, it may increase to couple of more feet, but not more than that, if you add an external antenna, than you will see the difference, so go ahead and try, you will be amazed by the range the antenna will offer you
phmanzano1 year ago
Thanks!
I finally hacked my FM transmitter with the help of this tutorial but found some differences on my model, see http://www.instructables.com/id/Alternative-Hack-for-FM-transmitter/ for details (wire antenna, hidden screws, bypass, ...). Hope this helps too. Since there's no FCC rules here I welcome better hack to improve my range :-)
poofrabbit1 year ago
Hey congratulations on being a finalist in the hack it contest! Good luck to you!
rbucher1 year ago
Is it possible to hack this one click here? I am only getting around 50 feet and would like to get more distance.
raikut (author)  rbucher1 year ago
I was not able to see the physical transmitter you have in the link you provided. What is the model of transmitter you have?
rcs-al2 years ago
From what I see on your pic, the piece you remove from the antenna circuit is not a resistor, maybe a capacitor or a coil.
raikut (author)  rcs-al2 years ago
Yes it is a Capacitor. You are right. But i have tested it as if you remove it and add an external antenna along with a small 107pF ceramic capacitor in between the antenna and the ground, the RF signal is much more concentrated between the antenna.
wa7jos raikut2 years ago
Increasing the power output of this device would be a violation of FCC rules.
These devices are limited to 100mw so as not to interfere with licensed operators.
If your modified device causes interference, you may get a nasty visit from the FCC, who can levy a fine of up to $10,000 PER DAY!
chrwei wa7jos2 years ago
Since raikut ins't in the US this may or many not apply directly.

As always, when dealing with licensed frequencies, be familiar with your local laws.
The FCC has jurisdiction over radio frequencies. No local laws apply, as far as I know. Not that they couldn't stop & hold someone & then inform the FCC I guess. Do you know something that I don't?
The FCC is local to the USA, but not to India, or Brazil, or the UK. Local doesn't always mean "the distance you can throw a rock".
True & India might be different as far as local governments having some jurisdiction over radio frequency usage. raikut would have to tell us that.
raikut (author)  PhilKE3FL2 years ago
Here in India, it is not like in the US.
The FM frequency spectrum is not much occupied at the place where i live. There are only 5 stations and one only broadcast in the morning.Therefore in total there are only 4 FM radio stations in Siliguri (QTH) And more or less there is no harm in transmitting on other free frequency. I had the urgency to make this hack because i had already told that my workplace is situated at a basement and there aren't any FM frequency penetrating, there fore i can use it here without any problem as it will not stray out from my workplace.
And yes, indeed here in India we do have regulations and guidelines that has to be followed. And there are consequences if not followed
ac-dc chrwei2 years ago
Waste of time in this case, and most... you can't just solder on an antenna and make much difference. Duh.
raikut (author)  ac-dc2 years ago
Well if you think it like that no hard feelings. I am living in a small village at a place in India, where not many are in the field of electronics. My love for electronics and elctronics gadgets are more that i can imagine. The work that i do for a living is a simple job of accounting, and the amount that i get paid here is nothing for you people there. It's just you would spend in a day. Life here in India is Hard, and i could tell better than anyone because i have faced it. Even after having such a hard life here in India, i like to share whatever knowledge that i have to people all around the world, and i have found instructables the best website ever to happen in my life. Whatever i have learnt is from by myself and i have never ever had the chance to learn electronics from any Colleges or institutes. I love reading lot of electronics books and if one tells me to stay all day having a Soldering Rod in you had i would be the happiest person to do so.
Please don't get offended as i wanted to explain that i am not a super hi-fi tech person who could write a really super instructable. I just tried and i am very much sorry if i have failed.
I have given a 100% in telling and reflecting whatever i had done and if you think it is a waste of time may be it is. I am very sorry that i was not up to your mark.
raihut,

Congrats on your ham license! I case you didn't catch it my call sign is in my user name, PhilKE3FL - KE3FL. Also, Instructables is here just for people like you who have figured something out that works for you.

Could it be done better? Probably. Does it matter if the transmitter now allows more frequencies out than it should? Not if you're the only one listening to the radio & it doesn't "bother" anyone else.

Good luck with the ham radio & I too hope your license comes soon, I know about the waiting, at lest when I got my license it only took three months. Now in the USA we can have a license the day after passing the test!
well get your HAM ticket ,,,,play in the world of radio with this the right way
raikut (author)  Fred826642 years ago
Yes Sir!!! Actually i have recently passed my Ham Operator License and i am waiting for my License to come up. As here in India, the process of obtaining a license takes usually more than a year, and i am on the line. I am praying that my license will arrive soon, so finger cross. If i do have this License than i will be the first in my city to have one.
Vary Good,,,I will be happy fro your QSO send me a message here with your call letters. at this point in time I can only run on Digital Moods like EchoLink . Apartment living has antenna restrictions so HF is not assessable for me right now
Raikut please do not be put off by some of the comments your work is a hack and you have enjoyed sharing your work with us carry on with the good work and keep posting I realise that you are making do with the hardship you have
Best of luck from UK
Raikut,
Do not get disheartened by some comments. I am only a physics graduate and learned Electronics all by myself. I also do automobile repairs, mechanical repairs, Electrical repairs etc. All I learned by myself. My friends and relatives tells me that I could get these works done by some one else, why take the trouble. I tell them that there is nothing to beat the mental satisfaction you gets from doing some thing all by yourselves successfully.
So keep doing what you are doing and be happy with it. When you are successful, Post it here for all others benefit.
One word of warning..
1) Please take appropriate precautions and follow safety procedures when doing any job yourselves.
2) Always use proper tools appropriate for that particular job.
wsecomp raikut2 years ago
You may want to think about joining the thousands of other East Indian immigrants that have come to the US because of the finances in India. I just heard this morning that the average income for a person with an engineering (i.e., electronic engineering, such as is your interest) degree is $92,000US (4,845,640 ₨) per year.
Sadly, that income level is incorrect, the entry level is much less than half that in todays job market IF one can find a job. Thes so called averages are not true figures and are used as recruiting numbers by Colleges and Universities. I, myself am a retired Electronics Engineer, and have seen newcomers constantly being disillusioned to the fact that they can quite often find more lucerative income in construction or certain factory positions, as they are not willing to "pay their dues" and work their way up the ladder to the higher paying positions they were lead to believe they could find right out of college.
nfarrow raikut2 years ago
Thank you Raikut for this instructable.
PhilKE3FL ac-dc2 years ago
Oh but you can. His will improve things a little but as it was said, if it solved his problem, served his purpose, then that's all that matters.

I once removed a small antenna & attached a BNC connector. I then plugged in my 144 - 440 MHz J-pole antenna on the roof of my house to a similar small transmitter. The difference was that with the J-pole antenna I was able to transmit all over my house & about half of my yard. With the antenna that came with the unit it could get to a few radios in the house but NOT to the kitchen & not any place outside.

I still have that little modified transmitter & it still works well but I wanted something a little more powerful. I wanted something where I could keep the antenna inside the house. The little transmitter I built can be adjusted from something around 1 mW or lower (I can't measure that low) & goes up to 25 mW was the correct choice for my situation.
It is a receiver, boosting the receive power means nothing, you can boost all you want, if it was a transmitter, that would be different
ac-dc wa7jos2 years ago
He isn't increasing the power output by much, this instructable is fairly redundant based on prior hacks by others, except to restate or remind that if you don't mind an external antenna you can add one of the right length for the frequency for a little gain.

Let's get serious here, there is no possible way he can produce enough power from 5V, let alone 3V, to have anyone else complaining and even if they did the FCC has better things to do than track down someone with a mW range FM transmitter. It's just not going to happen and even modified it will still produce lower output than other off the shelf FCC approved products, UNLESS there was an additional booster stage added with a higher drive voltage which is another hack for another day...

What I mean is, this is something people have done for years to their MP3 player add-on transmitters but with more detail than presented here.

To build a regulated power supply for a generic cheap Chinese transmitter seems like overkill, but on the other hand if the finished hack suits a need then it serves its purpose. I'd just start with something higher quality before spending more in time than the transmitter is worth.

The capacitor that was removed should stay there, it is used to filter undesirable frequencies.

Lastly, think about putting this in a shielded case with only the antenna outside.
quatch ac-dc2 years ago
Has anyone tried setting the gain higher using the i2c (note5 on p9)?
raikut (author)  wa7jos2 years ago
Well you are correct,
But as the title correctly says it is a Hack, and i suppose hacking are sometimes illegal. If you are able to find a free frequency in the FM spectrum at you place then no issues. You can just Google and find it out for you place. So you should be cautious while transmitting that you will not be interfering with local FM stations.
quatch raikut2 years ago
page 4 of the datasheet shows it to be an inductor. I don't know what that would provide here, not an RF engineer :( Maybe some frequency stability, or voltage modification.
An inductor makes a piece of wire electrically longer. It's called a loading coil. If you have a quarter wave (a couple feet at FM freq) antenna you don't need it, but if it's only a couple inches like the original, the inductor increases the voltage on the antenna so more gets radiated.
jimvandamme2 years ago
I got a car transmitter version, and rigged up a USB cable to a 12V socket that it plugs into. The chip inside runs fine on the 5V that the USB cord provides, although the backlight is a little dim. I use it to broadcast from my laptop into a nearby hi-fi, to get better sound.
PhilKE3FL2 years ago
1. The case is what is commonly called a sonically bonded case, it is not to be opened. So, of course I'll tell you the best way I've found for openeing it.
The best way I've found to open sonically bonded cases is very similar to what you did. If possible put it into a vice so that the vice puts pressure along the edge to be opened (No force the press the edge together but along the length of the edge. Then use a wedge (small knife) to push & pry the seam open & it should make a popping sound once it is separated. Sometimes the seam will pop without any wedge, other times it is very difficult to open the seam even with a sharp knife & the splitting pressure from the vice. As ? says, take it very slowly or damage will be done to the electronics inside.

2. Increasing the range. - Note, this is a part 15 (FCC - Federal Communications Commission) device and as such is non-licensed to operate as long as it causes no interference to any licensed operator. The more the power is increased, the more likely it is to interfere with someone else's reception of a radio station and the more likely the transmitter will become noticed by the FCC and the owner can be fined in the 10s of thousands of dollars for broadcasting illegally, without a license. The last case I've heard of just took place in FL (Oct 2012) & the person was fined $15,000 BUT, he was using far more power, an antenna on the top of the apartment building & of all things, had a web site saying he was broadcasting as radio station WXYZ (I don't remember the "call" sign he used) so the FCC NAILed him, shut him down, confiscated his equipment, and fined him $15K.

3. Avoiding trouble with the FCC over the increased power: I have an FM transmitter I put together that has an output from 1 to 25 mW (that's milliWatts) and where I live there are few free valid FM frequencies available so I put my transmitter on 88.2 MHz which is between two very weak stations on 88.1 & 88.3 MHz. Then I use an indoor antenna and only enough power to get to all the radios in the house. I then tested with a receiver, which can tune to 88.2 MHz, outside my house to insure that the signal does not get to any neighbor's yard let alone into their houses. Following similar precautions you should be fine.

4. The antenna: The "earth" of the 3.5mm socket was probably used as the counterpoise to the antenna. the antenna you said was a "coil" trace on the PCB. The length of a quarter wave antenna for 88.1 MHz would be about .85 meters, about 2 feet 1 inch. Since the target for this device is probably your car radio where the antenna is probably less than 5 feet away they figure not much power or much of an antenna is really needed. If the trace was directly attached to the ground side of the connector then what they are doing is using the "coil" to match the impedance of the output to the body of the car. Thus the body of the car is the antenna and so it is very close to the car's radio antenna & even getting inside the radio. Again, this would substantially lower the power needed to feed the signal to the radio's antenna.

Good work & stay safe (from the FCC) and I believe the output power of your device, even if 10 times more than it was originally, is probably still below 5 mW and even with an antenna, if you follow the guidelines above, you should be fine, well within the intent of the FCC rules & regs. If the FCC comes calling show them everything, cooperate, and turn it off & promise not to do it again, then don't ever do it again, & you probably won't even be fined. You might also tell them what you are trying to do and ask their advice & they may even be able to point you in a safe legal direction for accomplishing what you want to do.

Everything KE3FL says above is true, except .85 meters is about 33 inches.
If you can't receive your signal from the neighbor's house, the FCC will probably never come calling because they have better things to do. They won't notice unless somebody complains.
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