How To Boost an FM Transmitter

A tutorial on how to boost the signal strength of a Belkin Tunecast II FM transmitter.

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Jim Sullivan
P.O. Box 461748
Los Angeles, CA 90046

FM Jimplicit "FM Broadcasting" mod "FM Broadcast Band" Belkin tunecast II "Belkin Tunecast II" modify signal boost Radio ipod awesome lame "Frequency Modulation" F8V3080

[mitchellhoffmann]

Just ran out to radio shack and bought a soldering kit for this specific video. I tried it and it worked! I live in an area that has a ton of interference and it overpowered it all. Thanks for the video!

[hestheMaster]

Damn the FCC and Public Broadcasting FM radio stations for making us do this!

[ohiowalnut]

On the contrary, you do a GREAT JOB of explaining the task at hand! Thanks!

[bjtaudio]

The little black box you removed is the rf attenuation network, this is to maintain compliance for all countries, it also performs better if you use an external supply as the 3V battery supply uses a on board boost regulator that adds annoying hiss. The RF output is about 200uWatts I managed to get about 1mWatt by adding a bc547 single stage rf amp, easy.

[feeunit]

The spring-loaded clip is actually an aluminum heat sink to protect heat-sensitive components such as ICs when you solder them. You clip it between what you're soldering and the sensitive component and it prevents some of the heat from reaching the component. This is so you won't fry components soldering them in. If you use it as a wire clip, I guess it does two things at once.

[damon_]

Nice job. I did this same thing about 10 years ago. It works so much better, like 100x better. Im looking to repeat the process on a newer bluetooth fm transmitter. Thanks for the video.

[bill]

I did a Mod on my transmitter which is not a Tunecast it's just a cheap one I bought on Amazon, I have a quarter wave aerial tuned for 88.1 in an upstairs window and I get a good quarter of a mile "well over 1, 300ft" out of it running it from a regulated mains power supply. I'm in the UK and have run it this way for over 4 years with no problems at all.

[justinfoster]

Instructions unclear... People driving down the road are playing my music

[fullone]

this is super specific to this model of fm transmitter. I suggest you tag the model number

[reflowreflux]

that "little black box" is a transistor buffer used to isolate antenna from rest of circuit. if you simply adjust it's bias point you can increase the gain (and range). the same could have been achieved attaching the 'antenna' to the antenna point with out any soldering!

[Jimplicit]

That's really impressive! Sounds like you did an awesome job. I'd never even heard of an iRock before. Have you considered posting a tutorial for how to modify it, so that others with the same device can learn how to do that?

[RoyalH]

Why not just connect the blue wire to the new spot instead of a new black wire??

[Vyager]

There are several possible optimal lengths, but the shortest one would be a quarter wave length which is determined by the formula L=234/F which yields the length in feet (f is on MHz). Using the middle of the FM band, this would be 234/98 which is 2.39 feet, or 28.65 inches. This will work for any frequency. Ideally, you should have a counterpoise of equal length, but the power cord can serve in that capacity well enough.

[brettcooper]

What's interesting is that a lot of the car FM transmitters you get are actually overpowered, believe it or not. Especially the older ones. I have an old one from the early 2000s and I can plug it into my car in the driveway and still be able to faintly hear it on the radio in my bedroom. What that tells me is that this thing is putting out way more power than it should and is technically turning your car into a mobile pirate radio station.

[cjay]

Jim, that was crazy. As a longtime electrical engineer, I understood what you were doing, but what a crazy thing to do to that circuit! You apparently removed the output transistor (also antenna matching function) and have hung the antenna onto the transistor which preceded it.
Whatever. I cannot believe that a company would specifically print a statement on a soldering iron package stating that it wasn't to be used as a torture device. Darn! Now what? Shows the mentality the world has come to.

[hawwy]

I ended up taking it back, telling them why I was and they agreed that most have this problem. I listen to the radio on weekdays normally on a certain time so unhooking it would be out of the question unfortunately. Decided to get the Aux adapter for my focus instead. Thanks for the reply.

[bedwere]

Never mind. I couldn't wait for the answer, went ahead, and it works!

[coondogtheman]

I did this to an old iRock FM transmitter (yeah an iRock) and while having it on I tried different parts where those black boxes on the board were and some came in a little better and one point it came in crystal clear so that's where I put the antenna which was an old UHF TV antenna wire and It's about 3 feet long and I can pick it up all over the house it's awesome. I can even pick it up on all my weak radios.

[-_______________________.___]

I did this and the FCC kicked down my door and knocked over my cat's food bowl.

[lookoutleo]

Does it sound like as interference at low audio levels? Is their hiss when no music playing? I have same one and it's not great