Simple Fm Transmitter

joeypc · Dec 21, 2006

Hello Guys !
Does anyone here have a schematic of a simple fm transmitter ? Well... I'm just a newbie, so can anyone here help me ?
Thanks a lot !

Sceadwian · Dec 22, 2006

These are available everywhere on the net, just use google. If you're a newbie your first project shouldn't be an FM transmitter. Especially if you don't have a HAM license.

Hero999 · Dec 22, 2006

https://www.electro-tech-online.com/search.php?searchid=103900

joeypc · Dec 22, 2006

Hello "Hero999", would you mind checking this link again ? It said "Sorry - no matches. Please try some different terms."
Well, thank you all for suggestion about searching for schematics by using google, well I have another problem : I can't hold these circuits while operating, it will change the frequency. So I put the circuit into something like the microphone case or microphone cover or something that you could hold it like the wireless microphone, it also chage the freq. When I tried to hold the microphone cover and speak, the freq changed dramatically. So are there any solutions to solve this problem ? Anyone who have made wireless microphone sucessfully, so could you share the schematic(s) in this forum ?. Thanks for sharing the schematic(s). In my country radio transmission with the radius within 50 metres doesn't have to get a license.
Thanks !

audioguru · Dec 22, 2006

The cheap, cheap FM transmitter circuits change frequency when you get near them because the are simple and cheap and cheap. My FM transmitter has a transistor added to its output to isolate the tuned circuit from the antenna and to boost its output. It goes more than 2km so it is very illegal. I guess its power can be turned down.

My FRS transeivers were a bargain with their crystal frequencies, rechargable batteries, 38 channels and 3km range. I didn't make them and never looked inside them.

Hero999 · Dec 27, 2006

**broken link removed**

bananasiong · Dec 27, 2006

Is it very difficult to search by ur own? Unless u don't know that there're discussion about this topic or u have question.
**broken link removed**

joeypc · Jan 20, 2007

audioguru said:
The cheap, cheap FM transmitter circuits change frequency when you get near them because the are simple and cheap and cheap. My FM transmitter has a transistor added to its output to isolate the tuned circuit from the antenna and to boost its output. It goes more than 2km so it is very illegal. I guess its power can be turned down.

My FRS transeivers were a bargain with their crystal frequencies, rechargable batteries, 38 channels and 3km range. I didn't make them and never looked inside them.

Hello audioguru, if i don't use an RF amplifier at the output, so are there any onther solution(s) to prevent from frequency drifts or changes when anything gets near the transmitter ?
Thank you !

Sceadwian · Jan 20, 2007

Sure, don't get near it =)
You'd be better off simply using an MP3 player RF transmitter and sending it's output into an amplifier or makeing a better antenna. Just makeing a better antenna is going to double or quadruple the range of one of those MP3 jobbies.

Hero999 · Jan 20, 2007

No.

joeypc said:
Hello audioguru, if i don't use an RF amplifier at the output, so are there any onther solution(s) to prevent from frequency drifts or changes when anything gets near the transmitter ?
Thank you !

There isn't, either build and output amplifier as the schematic suggests or put up with the frequency shifting when the load on the oscillator changes due to reflections.

audioguru · Jan 20, 2007

The cheap FM transmitters have the antenna connected directly to the tuned LC so of course the frequency changes when the capacitance of your body or anything else gets near the antenna. The cheap circiut's ground is also part of its antenna system.

The frequency is also set by the capacitance of the oscillator transistor that changes as the battery voltage runs down. Cheap FM transmitters don't have a voltage regulator like my circuit has.

The FM transmitters sold to transmit an MP3 player to a car radio are very poor and very good. The good ones are stereo, have excellent frequency stability due to their quartz crystal controlled frequency synthesizer and have a fairly high output that is attenuated. The poor ones are mono with bad sound and are junk. The poor ones cost the same as the good ones.

Hero999 · Jan 20, 2007

The question is how do you differentiate the good ones from the poor ones?

audioguru · Jan 20, 2007

I have seen them in stores.
The good ones have DIP switches to select 4 frequencies near the bottom of the FM dial and 4 more for the high end. That sets up the quartz crystal controlled frequency synthesizer like in the Micromitter project.

The poor ones don't have DIP switches. I can't remember how they are tuned. Maybe just by getting near them.

Overclocked · Jan 20, 2007

audioguru said:
I have seen them in stores.
The good ones have DIP switches to select 4 frequencies near the bottom of the FM dial and 4 more for the high end. That sets up the quartz crystal controlled frequency synthesizer like in the Micromitter project.

The poor ones don't have DIP switches. I can't remember how they are tuned. Maybe just by getting near them.

Ive seen the cheap ones around, I forgot where (dollar store? Maybe newegg..) that have a fixed Freq on the Lower End of the Spec (88.7Mhz I believe- Dont quote me on that). Ive thought of Buying the cheap ones to see whats inside and *possibly* hacking it to be adjustable..

things · Jan 23, 2007

fm transmitter

is there any way to amplify the output from my fm transmitterbecause it only transmitts obout 50 meters. i,ve tried increasing input power but it just cuts out. i,ve tried adding a bigger antanna
but i didn't notice a difference. do you know any way to amplify the signal without the use of any complicated stuff like ic's

audioguru · Jan 24, 2007

Adding a simple RF amplifier can boost the range and increase the frequency stability of an FM oscillator.

Some FM transmitters use a transistor RF amplifier with a resistor as its load. My FM transmitter uses a tuned circuit.

Here is one with a transistor RF amplifier using a PNP transistor. An NPN transistor could be used instead.

things · Feb 1, 2007

fm transmitter

is there any way to amplify it with some transistors and easily avaliable components. so i can build it myself i'm not that good at electronics. i've also got a picture if that will help

things · Feb 1, 2007

fm transmitter

i also have some diagrams to help.

audioguru · Feb 1, 2007

Hi Things,
How is the performance of your old BA1404 stereo FM transmitter kit?
Rohm made the old BA1404 IC (it is obsolete) and has replaced it with the much better BH1417 that is used in the Micromitter project.

The old BA1404 did not use a crystal for its RF oscillator so it drifted its frequency all over the place. Its stereo 19kHz and 38kHz uses a crystal but their harmonics cause interference with its RF oscillator.

These ICs are made to transmit a few meters from a MP3 player to a car radio. I don't know about an RF power amplifier for them because using one would cause interference with other radios and would be illegal.

things · Feb 1, 2007

fm transmitter

i don't intend transmitting very far but a bit more than it can now. Do you have any diagrams for a simple amplifier i can build. i wat to be able to link the amplifier to the antenna output. Is this possible?

thanks

Simple Fm Transmitter

New Member

Banned

Banned

New Member

Well-Known Member

Banned

New Member

New Member

Banned

Banned

Well-Known Member

Banned

Well-Known Member

Member

New Member

Well-Known Member

Attachments

New Member

New Member

Well-Known Member

New Member

Similar threads

Privacy & Transparency

Privacy & Transparency