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.
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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Signing UpStep 1: Opening the shell
As i was shown various ways in instructable itself on how to open the transmitter, i was a bit surprised with my gadget. I had seen that in instructables posted to instructables it was shown that the FM Transmitter was hold up by only one screw and rest were just popping up the case.
But in my case i was surprised because there weren't any screws holding the Transmitter. I tried to pop it open but was unsuccessful. I tried and saw various opening to find if there were any hidden screws holding the unit. To my frustration at the end i found out none. Then by hook or by Crook i had to get inside therefore i made up my mind that i would open it, if also i had to break it.
Then i steady put up a wedge inside the shell and forced it to make a gap. I put a second wedge and again forced to make a more bigger gap. Still i was not able to see any screws from the gap. I continued till there was a breaking point. Then after a final push, there was large pop sound. Here i found out that this gadget was not held by any screws.
The Company had made this product so that it was not serviceable, that no body would be able to open this product. I could see that the legs holding the gadget had broken, and in no way i wold be able to put it back like it would have been before. I had to think for that also. But on the other had i had successfully opened the shell.
I guess this process of fixing it permanent was done deliberately so that no one like me could open it. But nothing was going to hold me back. I had successful opened the shell. But i would like to caution to the reader that this was process that i followed was done in a very slow and steady process, don't hurry up as you may end up damaging the PCB of the Transmitter.
But in my case i was surprised because there weren't any screws holding the Transmitter. I tried to pop it open but was unsuccessful. I tried and saw various opening to find if there were any hidden screws holding the unit. To my frustration at the end i found out none. Then by hook or by Crook i had to get inside therefore i made up my mind that i would open it, if also i had to break it.
Then i steady put up a wedge inside the shell and forced it to make a gap. I put a second wedge and again forced to make a more bigger gap. Still i was not able to see any screws from the gap. I continued till there was a breaking point. Then after a final push, there was large pop sound. Here i found out that this gadget was not held by any screws.
The Company had made this product so that it was not serviceable, that no body would be able to open this product. I could see that the legs holding the gadget had broken, and in no way i wold be able to put it back like it would have been before. I had to think for that also. But on the other had i had successfully opened the shell.
I guess this process of fixing it permanent was done deliberately so that no one like me could open it. But nothing was going to hold me back. I had successful opened the shell. But i would like to caution to the reader that this was process that i followed was done in a very slow and steady process, don't hurry up as you may end up damaging the PCB of the Transmitter.
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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 :-)
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.
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.
Sometimes I've use a plastic solvent to bond them back together and other times I've found a way to use a screw or two or three to hold the case together. It all depends on if I think I'll want to get into it again some time later or not.
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!
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.
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.
As always, when dealing with licensed frequencies, be familiar with your local laws.
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
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.
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.
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!
Best of luck from UK
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.
The first picture is where i keep my unit. You can see the antenna.
Second is the adapter that i connect with my PC 3.5mm socket.
The third is the one transmitting at 87.50 Mhz. I use this frequency as i have seen that the range is more extended while at lower frequency.
The fourth shows the junction adapter in large.
And lastly i have added a picture of the power supply by a USB adapter powering the unit.