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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"?
you could just turn your speakers all the way up.
If you play music, can the RIAA sue the air for abetting the distribution of copyrighted material?
UTF-8: There and Back Again
The VHF broadcast band is a regulated resource. What you have created is, in effect, a pirate radio station with all the regulatory and copyright issues that that entails. If the FCC/Ofcom or whatever regulatory authority covers your area doesn't take an interest in your "personal radio station" in fairly short order, I'll be very surprised. The performing rights organisations may take an interest, too.
In short, you will be very lucky if you get away with this for long.
Resistance is futile. Reactance buggers it up.
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.
Going to the store page reveals that a 0.3W transmitter costs a wild $140. Yes, there's an LCD and menus, but no self-respecting budget-minded geek would lay down that much money to broadcast music over a short distance.
There's plenty of circuit designs at ePanorama that are relatively simple and powerful. DIY; save your money and your honor.
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.
On FM frequencies, these devices are limited to an effective service range of approximately 200 feet (61 meters).
/ Documents/bulletins/oet63/oet63rev.pdf
source:
http://www.fcc.gov/mb/audio/lowpwr.html
see also:
http://www.fcc.gov/Bureaus/Engineering_Technology
Bottom line:
The transmitter described is not even close to complying with FCC regs. FCC compliance depends not only on transmitter power, but also on antenna gain and several other factors. You cannot simply say "X milliwatts is safe". Not only that, but 100mW into almost any antenna is going to be a violation. Something in the range of 1mW into an omni antenna would be more like it.
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All of whose base are belong to the what-now?
If you just want a radio station in your home it would seem to make more sense to use a Carrier Current transmitter. What this guy is doing is pretty damn illegal and if you do what he did you can be looking at tens of thousands of dollars in fines!
From what I can tell anyone can setup a Carrier Current station(check for yourself), you can find some pretty cheap kits.
This guy doesn't seem to be all there, he says he has a HAM licence, but is stupidly violating FCC laws. He also says the thing has a BNC type connector but the picture looks like a type RG6 connector.
In Europe it is not permitted to use any transmitter on broadcast frequencies, unless you are a licensed broadcaster. And it doesn't matter how low the output power is, so those Ipod thingies are not allowed either.
Think about it, grab a embedded linux system with onboard sound and network (wifi or ethernet), have a central server broadcast non-RIAA regulated tunes, then find people willing to stick one of these up where they live. Have enough people do this around the area, and boom, you have a radio station which the RIAA can't touch (because they don't regulate the music on it), the FCC can't exactly complain about (broadcast power on each node doesn't warrant a license right?), and annoying the hell out of the local commercial radio stations.
The only problem I could see is keeping each broadcast node in sync, especially if you're all broadcasting on the same frequency.
Thats people power for you.
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
One of my hobby projects is searching the shed and attic for the $5 FM sender (100mW) that I once bought and soldered together to experiment with digital transmission (wanted to hook it up to the serial port) through the radio (cheap...). It would kill any other radio station using the same frequency in my block, and it could be received throughout the street (we did not live in a very long one though). I used half a meter of copper wire as antenna.
I wonder why (1) they are no longer for sale at all in the Netherlands (Velleman kit), and (2) why the alternatives cost over ten times that much, and provide less than a fraction of the output.
Musicians don't die. They just decompose.
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.
Bruce
Bruce Perens.
Bruce
Bruce Perens.
I am not plugging EITHER of those transmitters, because I'm not USING either of those transmitters.
I AM plugging the utility of having an FM transmitter in the home, because I'm doing it and it is truly useful... I rate it as highly as a fileserver or my wireless link.
Keep in mind, too, that not all transmitters have good quality sound. I'd be leery of the cheap ones.
Murphy was an optimist.
I bought one of those little consumer FM transmitters (this was a Belkin model) that you're supposed to plug into the audio jack of your MP3 player, but it really sucked. The main issue is that reception was so bad it was unacceptble even if I put it on top of my car dashboard.
So, since the thing was so useless I was out thirty five bucks anyway, I took it apart. The antenna turned out to be a length of wire about two inches long stuffed into the same cable used for the audio jack. Obviously, this was nearly worthless. I drilled a small hole in the case and soldered in a piece of wire the right length for a half wavelength antenna -- a little less than 63 inches for the low end of the FM band. As a result, I can now broadcast all over my house.
Now, since I was using it in a car, a five foot piece of wire was a bit unweildy, so I wound it around a pencil to make a loopstick antenna. I don't know anything about designing loopsticks, but it still worked OK for broadcasting around the house. Basically, I'd guess just about any length of wire a few feet long would work way better than the tiny length of wire they were using.
The only remaining issue is that the volume is very low; you have to jack up the volume on your receiver nearly all the way to get acceptable listening levels. If you're planning on driving around town with your windows down so your car's subwoofers won't blow them out, this is not for you. Also, the sound is a bit muddy. I suspect that in order to avoid any FCC issues, they took a number of steps: using a low transmit power, using a worthless antenna, filtering out the high end audio frequencies, and undermodulating the signal. I could probably desolder and replace some resistors and capactitors or something if I were motivated enough to analyze the circuit. Plus, as an old fogie I'd have to learn to deal with surface mounting (I learned to solder on bakelite terminal strips for chrissakes). Altogether this is too much trouble.
I'd recommend that if you bought one of these consumer MP3 transmitters and found it totally worthless, then you should replace the antenna with any old piece of wire and it will gain enough range to be some use to you. If you haven't bought one yet, don't. Getting a device like this guy is using would be a bit more expensive but probably a lot more satisfactory.
Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
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...
If you wish to assert that FCC sends the hostage recovery team to prosecute teenagers for out-of-spec transmitters that interfere with private microwave links and sends their moms to jail for 5 years, you will have to show:
Bruce
Bruce Perens.