Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Fm Transmitter Help

Status
Not open for further replies.

Griffr33

New Member
I'm looking to build a FM Transmitter to use around my house, i want to make one that has a large range. i want to make one that can brodcast around my neighborhood. Would 1 Watt be enough for that? and could someone help me with schematics?
 

Hero999

Banned

audioguru

Well-Known Member
Most Helpful Member
It is against the law in most countries to be a broadcaster without a licence. A licence needs a certified transmitter, not home-made.
They are worried that you might broadcast bad things or cause direct interference to other FM radio stations or indirect by the harmonics causing TV and communications interference.

The web is full of high power transmitters and RF amplifiers with horrible designs.
Some companies make kits for radio pirates.
 

AllVol

New Member
It is against the law in most countries to be a broadcaster without a licence. A licence needs a certified transmitter, not home-made.

Some folks here are using legally-purchased FM transmitters to broadcast music and narration with their outdoor Christmas light displays. The range is limited to a few hundred feet, and one can pick up the broadcast on their auto FM receiver while watching the show.

I think the FCC makes allowance for this activity through power and distance limitations.
 

stevez

Active Member
I googled on "fcc fm transmitter" and looked at several websites and publications that seemed to be credible sources of information. I read that for unlicensed operation within the FM broadcast band that the limit is based on 250 microvolts per meter of field strength at 3 meters from the transmitter (other conditions apply). One of the sites showed an example with calculations that suggested 1 watt was several orders of magnitude more power than might be allowed. Each country has it's own rules but the US rules provide some insight.

Based on what I read and a little bit of experience I'd suggest that you could purchase a certified compliant (for your location) commercially available transmitter that includes an antenna and use it as indicated by the manufacturer. You are responsible for the emissions but it's likely that you'll be ok. If you choose to build your own then you accept the responsibility for design and operation.

In the US, and possibly other countries, they do not have large numbers of radio police to monitor this kind of activity. There are however, lots of people who could be affected by a transmitter and if you bother them enough they will find you and if required, ask the authorities to enforce the regulations. This might suggest that if you live in a rural area and use very low power, that the odds of bothering anyone are relatively low - and then as the population density increases, the odds of bothering someone increases. One could also argue that there is so much junk in the RF spectrum it might be tough to single out any one offender - though I can say that I've worked with teams locally to track down spurious emissions - usually but not always some malfunction.
 

HiTech

Well-Known Member
I'm not sure if this particular FCC rule has been updated, but long ago it was determined that the antenna could not be more than X feet from the transmitter as well as X feet above earth ground. So, the trick some of us would do to circumvent that was to place the transmitter high up on a tower along with the antenna and simply run DC power and audio to it!! :rolleyes::p
 

stevez

Active Member
A quick look at a website or two suggested to me that the rules for the FM broadcast band are different than for the AM broadcast band. My memory of the way things were is similar to yours - basically allowed hobbyists to be compliant with less knowledge. My friend's phono-oscillator was one of the things that sparked my interest in electronics - a simple but effective transmitter connected to his phonograph.

I suppose it's like other rules and regulations - they change as people find creative ways around the existing rules.
 

mneary

New Member
**broken link removed** (US regulation) hasn't had substantial changes in quite a while. Imho, it's not difficult reading, but it may test your attention span. ;)
 
Status
Not open for further replies.
Top