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An FM Broadcast Transmitter For Your Home
Bruce Perens writes "I wanted to be able to listen to net audio and my ham station around the house and yard. Those iPod FM transmitters don't have enough range. So, I bought a digital controlled, 100 miliwatt transmitter that covered my whole block the first time I plugged it into what was, until then, a recieving antenna."
Now every kid on the block will have their own radio station!! won't that be fun for like.... a week?
Just look in the DIY kit section of any electronics store, there's always a number of small FM transmitters, some of which get 2km range.
They usually have an electret microphone, but it wouldn't be very hard to modify one to take a line-level source.
All the images on the linked page are exactly the same as the site selling them.
... has similar stuff - like this. And that's not the only one. they do various versions for, say, in-car use.
interesting way of sharing music - your own mini radio station
Screw you all! I'm off to the pub
if lots of people in the same block start using this?
.at least in europe it is almost completely filled up in the range that all commercial receivers use.
Is there some sort of auto free-carrier slot detection? because if there isn't, it will be nigh-on impossible to listen to the radio without interference.
The fm-band is pretty full already
I'd be pretty miffed if i could not receive my favorite radio stations anymore because some people near me like to listen to deutche schlager zangers or techno.
Didn't we all learn our lesson from "Pump up the Volume"?
If you play music, can the RIAA sue the air for abetting the distribution of copyrighted material?
UTF-8: There and Back Again
Be careful
Here in Israel there are a number of pirate radio stations. This is not itself a problem but they are using poor equipment and blasting harmonics onto aviation frequencies. That is bad. It has gotten to the point where the ATC folks have threatened to strike if something is not done about it because it can threaten aircraft communications.
Erlang Developer and podcaster
It used to be. As a ham you SHOULD know this. The rules regarding unlicensed broadcast transmission in the FM band changed. You can, in fact, use any amount of power you want. That is, as long as you don't excced 250uv/meter measured at a range of three meters.
For most of the unlicensed stuff that translates to roughly 10 to 20 mw. This is governed by part 15 of the FCC code and you can read even more about it at http://www.fcc.gov/mb/audio/lowpwr.html#PART.
That would have been great for around the farm when I was a kid.
While driving the tractor about 60 hours a week throughout the summer, I had my choice of precisely two stations. One was country and western and the other covered things like little league baseball games and the farm reports.
There still would have been a problem -- I didn't have anything at home that would have been worth broadcasting. After all, attaching a microphone and listening to the dogs barking occasionally would have gotten old real quick.
1: You might get surprisingly long range reception. From my experience on the 145 MHz Ham band, I can easily communicate 30 miles with less than 1 watt with a roof-mounted antenna (of course the receiving station also has a good high antenna). There are differences that will reduce your range (particularly the wide bandwidth of the signal), but in general 2 watts can potentially cover a very wide area..
2. Yes, particularly if the antenna is high up and your signal gets into the city, or if your transmission annoys anybody for any reason.
3. $10,000 a day fines and your equipment (and possibly other nasty things I don't know about!)
Ultra cheap FM transmitters use a tuned tank circuit to control frequency (ie - a variable capacitor). These are very difficult to get to the exact center of the frequency you choose, the result will more than likely be poor audio response.
Furthermore, your receiver is probably digitally controlled to an exact FM frequency and the variable cap system will change frequency slightly with temperature and humidity, so that the transmitter will slowly go in and out of channel. The receiver is phase locked to the correct channel, and the result is that the system will gain and lose quality over time. Digitally controlled frequency is a must for this application.
Kit systems are usually poor at doing audio; making a noise-free circuit is somewhat of a black art and it takes a lot of research and tinkering to get it right. For example, Ramsey Electronics makes an FM transmitter kit with digital frequency control and all that. The problem is that the board layout introduces an unacceptablt amount of hiss into the audio signal. No amount of adjustment will fix this, and the average hobbyist is unprepared to even figure out what the problem is.
Finally, Be very careful of high end ($300) transmitters used for gyms. Some of them are mono only (!) but do not specify this on the advert.
Your best bet is to look on the net for reviews of any transmitter you're thinking of buying. When people have good things to say and don't point out the obvious flaws, then the product might be OK.
I purchased several poor FM transmitters before I got one that worked well, and I use it for transmitting FM throughout the house.
That would be the C.Crane FM transmitter. You can get it for about $80, and Froogle lists several vendors.
I was currious too so I did a rough google search, but not interested enough to refine it.
I did however, run across an entertaining article by a pirate radio guy. As a bit of CYA, I whole-heartedly do not recommend breaking the law nor would I suggest taking the article as "truth". It's just fun to read - on to the excerpts:
... Having been visited twice before by the FCC, veteran broadcaster Monk briefed us on what the risks were and how we should handle a visit (see below). We were prepared.
Nonetheless, the FCC visit I experienced was bizarre. I woke up to find two strange men in suits and a uniformed cop in my front yard.
What changed under Obama? Nothing Good
We've had a similar transmitter in our house for a few years now, and I do recommend it for parties. Basically, the setup is:
1. Switch on machine with mp3 store
2. Create vast randomised playlist
3. Switch on the transmitter
4. Switch on every radio in the house
5. Open case of beer / chosen drink
6. Party party party!
And voila, synchronised music in every room that wants it.
One issue though is that we have to drop the output power of the transmitter to avoid interfering with anyone else's radio - here in the UK they don't take too kindly to that.
or how about anyone come over..
what he is doing is already in violation of the FCC rules. 100 miliwatts is the maximum allowed into the antenna provided in the kit. hooking it up to a gain antenna is illegal as he now went past the 100mw ERP.
all it will take is one phone call by a pseron that does not like him to get the FCC and a 10,000.00US fine on his arse.
Unlicensed operation on the AM and FM radio broadcast bands is permitted for some extremely low powered devices covered under Part 15 of the FCC's rules. On FM frequencies, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR (Code of Federal Regulations) Section 15.239, and the July 24, 1991 Public Notice. On the AM broadcast band, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR Sections 15.207, 15.209, 15.219, and 15.221. These devices must accept any interference caused by any other operation, which may further limit the effective service range. For more information on Part 15 devices, please see OET Bulletin No. 63 ("Understanding the FCC Regulations for Low-Power, Non-Licensed Transmitters"). Questions not answered by this Bulletin can be directed to the FCC's Office of Engineering and Technology, Customer Service Branch, at the Columbia, Maryland office, phone (301) - 362 - 3000, e-mail LabHelp@fcc.gov.
PENALTIES FOR OPERATION WITHOUT A PERMIT OR LICENSE
The Commission considers unauthorized broadcast operation to be a serious matter. Presently, the maximum penalty for operating an unlicensed or "pirate" broadcast station (one which is not permitted under Part 15 or is not a Carrier Current Station) is set at $10,000 for a single violation or a single day of operation, up to a total maximum amount of $75,000. Adjustments may be made upwards or downwards depending on the circumstances involved. Equipment used for an unauthorized operation may also be confiscated. There are also criminal penalties (fine and/or imprisonment) for "willfully and knowingly" operating a radio station without a license. DON'T DO IT!
He also far exceeds the distance limit set by the FCC.
Nice way to publically admit you are violating FCC rules.
Do not look at laser with remaining good eye.
Program restrictions are not relevant for my purposes, which are not broadcasting. Those who want to open a broadcast station for their own neighborhood can potentially run into them.
Bruce
Bruce Perens.
The terrorists have already taken over. ClearChannel killed my favorite 35-year-old rock station in favor of Latino hip-hop. If that's not terrorism, I don't know what is...