DIY FM Broadcast transmitter

This is a crude, yet effective broadcast FM transmitter i built from scrap parts laying around the shop, back in 2006. the heart of the system is the old belkin tunecast 2 circuit. it had a cracked screen so i used the transmitter itself as the PLL system. it was tested at the campground in 2007 and it performed well all summer before decommissioned in favor of the ipod on the golf cart instead of a regular radio.

Category:

Science & Technology

Tags:

• DIY
• FM
• RF
• broadcast
• transmitter

[leftist]

I would be very interested to watch you do a video on building a RF AMP fopr the out put of one of those Belkin/Irock?blah cheap fm transmiters. I have not found any tut videos on building RF Amp on YT yet :( . Everybody is after ciruct is built testing it out. Your seems nice and smiple. Anyways great build thanks for sharing.

[THEtechknight]

@leftist Well, I have the full schematics of the unit. I could post them on megaupload or something?

[bjtaudio]

@leftist Also the sound quality of these mini transmitter units is poor. To boost a mini transmitter such as the belkin tuncast 2 or 3 to 100's of milliwatts or even more you need a massive amount of RF gain and a number of shielded and well isolated stages to keep the dam thing stable. You can boost the units by removing the attenuator resistor network inside, and fitting an external antenna.

[THEtechknight]

@bjtaudio The sound quality is great if you dont over-modulate it of course. if you begin to overmodulate it, at even 1% it will have aliasing/distortion effects and also itll splatter all over the sidebands.

Thats the BAD about these PLL ICs. but other than that, the IC runs good.

[mumish13]

how much are the range?

[THEtechknight]

@mumish13 Depends on how the antenna is setup and where its located, obstructions, etc etc etc... at the campground we got about 3 and a half miles, up to 4 miles between the transmitter and US101 where it faded in to static.

at my house, it would go about a half a mile and it fades out.

[ttargia]

Can u make one for me i would love to have something this powerful?

[Lacika00]

Hy!

I read that you can share the schematic for this Radio. If you could send me, it will be very good, because i whant to build a PLL radio transmitter. :)

Thanks.

[bjtaudio]

@bjtaudio I'd like to spread the message to everyone that uses FM transmitters like the Belkin tune cast 2 or 3 and has issues with the static and poor range, and the fix is to remove the attenuator network, use an external power supply, and fit an external wire antenna about 0.5Meter is ok. The antenna currently is run inside the audio input cable which is shielded, a stupid idea, where almost no signal is radiated at all 1uWatt maybe if that..terrible! 10micoWatts is the limit in Aust.

[bjtaudio]

@THEtechknight Yep your right I using a audio compressor to limit stop the over deviation and it sounds like a real station. Also I noticed that the built in switch mode powersupply that boost the 3V from the battery supply to 5Volts or so to run the chip in the Belkins tunecasts units created an unacceptable level of background hiss. By using an external dc supply avoids this problem. From memory I was able to get about 100~200microWatts into 50Ohms from the Belkins, attenuator removed.

[bjtaudio]

@leftist Yea I made such mini amplifiers ranging from a few milliwatts to watts, and the results are mixed. As the power increases past a few 100 milliwatts it starts to disrupt the electronics in the mini transmitter as it become almost impossible to stop of the high power rf leaking back into the PLL circuit .

[bjtaudio]

With PLL and audio level meters it's not crude, there are some absolute rubbish kits out there!

[leftist]

@THEtechknight

Yeah that would be nice. I was speaking about a Vtut cause all the others are just talking about a completed unit, just thought it would be neat.