Help me get parts and build a fm transmitter

[antaean3000]

fm transmitter

I am from the uk and i have never done electronics before however i have someone who can help teach me how to solder and use the components.

What i want is to build a fm transmitter about 1watt or maybe even 5 watt
ideally i would like to buy one but some places sell them they are £500 i figured it would be cheaper better and more fun to build your own.

I look at schematics like this one

and i don't even know how to understand them let alone where to get the parts.

Any help or tips on where to start or how to find the parts would be cool.

 

[Audioguru]

fm transmitter

It is illegal to use such a high power transmitter without a licence. The licence will specify the type of programs you can play and the frequency you can use if a frequency is available.

The transmitter must be certified not to cause interference.
This simple circuit will probably cause interference to real radio and TV stations.

It doesn't have pre-emphasis so it will sound awful on an FM radio.

 

[antaean3000]

Re: fm transmitter

It is illegal to use such a high power transmitter without a licence. The licence will specify the type of programs you can play and the frequency you can use if a frequency is available.

The transmitter must be certified not to cause interference.
This simple circuit will probably cause interference to real radio and TV stations.

It doesn't have pre-emphasis so it will sound awful on an FM radio.

The legality of it is that it is legal to transmit short distances i believe its up to 500meters or so.

I just want to transmit from one part of the house to another. 1 watt or 500mw wont transmit far if you use a small antenna inside your house

 

[Audioguru]

fm transmitter

If your neighbours are 500m or more away then you will not cause interference to them with a very low power transmitter.

Instead of blasting high power to a cheap insensitive radio then use low power and a very sensitive radio.

If you want quality transmissions then use an MP3 to car radio FM stereo transmitter that has excellent sound and remove the RF attenuator it has at its antenna. Then it will cover your house and yard.

 

[keith1200rs]

fm transmitter

I cannot remember the regulations about the power you are allowed to transmit but it is something like 100uW NOT 1W!

If you do want to build something like that I would suggest you look at kits with instructions. I am out of touch with those things but there were a couple of UK companies who did them - Veronica was one.

Keith

Added after 1 minutes:

Bear in mind it will cost a lot more to build one than buy one (the correct type - not a broadcast FM one).

Keith

 

[betwixt]

Re: fm transmitter

At least give Antaean3000 credit for finding a frequency stable design although I suspect getting hold of some of the parts may not be as easy as it seems.

Take note of Audioguru's warning about pre-emphasis. I'll try to explain it in laymans terms: You probably noticed a weak FM signal has background hiss, some of this is actually in the transmission and receiver circuits but the vast majority comes from random signals being picked up and amplified from the antenna. The hiss is most noticeable in the mid and high sound spectrum, you can see this if you play with tone controls on your FM radio, the bass control makes little difference to the noise but the treble has a pronounced effect. In FM audio transmission we take advantage of this by using pre-emphasis at the transmitter and de-emphasis at the receiver. As their names suggest, some frequencies are emphasized and reduced in the process. Pre-emphasis at the transmitter boosts the mid and high sound frequencies by a fixed amount so the 'real' transmission sounds harsh and 'tinny', to compensate, the receiver reduces the frequencies by the same amount in the de-emphasis circuit. The combination restores a flat frequency response as far as the sound is concerned but the background hiss which is introduced between the transmitter and receiver output is quite dramatically reduced. You might like to think of it as turning the treble control right down on your receiver and turning it right up on the transmitter to compensate.

If you use the design as it is, it will certainly work but because it doesn't have pre-emphasis, the sound will be transmitted as it is but the receiver will still try to reduce the volume of higher pitched notes. the result will be very muffled 'muddy' sounds.

As far as power is concerned, even 1 Watt could reach several miles and unless you live in a metal box, it will spread outside in all directions. Your neighbors would be able to listen in and it's highly likely you would cause interference to others. There are strict licensing conditions you have to comply with, you can get the details from the Ofcom web site. Even if you ignore the license, to broadcast around the home you wouldn't need more than 5 - 10mW, in other words less than 1% of the power you are proposing.

Brian.

 

[antaean3000]

Re: fm transmitter

Thanks Brian. I do not know much about watts and stuff i said 1watt because i thought that was not very powerful.

In response to going out and buying one where is the fun in that? the sense of achievement if you built your own instead.

I have a fm transmitter i brought from pcworld costs me enough and it wont transmit from one room to the next as soon as you walk out the room it starts to hiss and when you left the room no signal at all.

the other one i have us a usb linex which is better but you cant hook up your ipod to it because its usb and only recognized by your computer the range is good on that it will broadcast in to our car park.

But this is the only house out here for miles that's the beauty of leaving out in the sticks.