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Toys Communications

An FM Broadcast Transmitter For Your Home 417

Posted by CowboyNeal from the on-the-air dept.
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."
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An FM Broadcast Transmitter For Your Home More

An FM Broadcast Transmitter For Your Home

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  • wow (Score:5, Funny)

    by Tickle Cricket ( 845932 ) on Friday January 07, 2005 @02:05AM (#11285465)
    Now every kid on the block will have their own radio station!! won't that be fun for like.... a week?

    • Re:wow (Score:3, Funny)

      by tuxter ( 809927 )
      Don't forget, the mental agility of the aforementioned participant is inversely proportional to the length and volume of pleasure. i.e. the stupider you are, the funner it is for longer.

      • Re:wow (Score:3, Interesting)

        by Fig, formerly A.C. ( 543042 )
        I've had my own FM station on a military surplus transmitter for a year, and it's still fun.

        I have a dedicated headless machine on my LAN running WWWinamp (http://www.nullsoft.com/free/wwwinamp/)playing from my MP3 server, and the output from the soundcard goes into my transmitter. I can queue up music from any web browser on my LAN, and hear it all over the house (unlike a tethered PC system).

        Plus, everyone that comes to my LAN parties (~24 people) like the ability to have the "Electronic DJ" take requests

    • Re:wow (Score:5, Funny)

      by totipotentsoul ( 828085 ) on Friday January 07, 2005 @02:17AM (#11285525)
      Bart: [over the radio] Rod! Todd! This is God!
      Rod: How did you get on the radio?
      Bart: Whaddya mean, how did I get on the radio? I created the universe!
      Stupid kid.
      Todd+Rod: [fall to their knees and clasp their hands]
      Todd: Forgive my brother. We believe you.
      Bart: Talk is cheap. Perhaps I'll test a guy's faith. Walk through the wall! I will remove it for you.
      Rod: [walks into the wall] [thud]
      Bart: Ha ha ha.
      Todd+Rod: [return to their knees in prayer]
      Todd: What do you want from us?
      Bart: I got a job for you. Bring forth all the cookies from your kitchen and leave them on the Simpsons' porch.
      Rod: But those cookies belong to our parents.
      Bart: Ugh! Look, do you want a happy God or a vengeful God?
      Todd: [quickly] Happy God.
      Bart: Then quit flapping your lip and make with the cookies!
      Todd+Rod: Yes, sir!
    • I wish i could remember the name of the movie but it's been done. He sets up a radio station when he moves into town and rants on about life. The local kids start listening and someone commits suicide. The guy gets chased by the FCC if i remember rightly...
    • Luckily or Unluckly for us over the pond, FM transmitters such as these are illegal in the UK.

      Here, we cannot have a personal transmitter that works over the normal FM radio band, which is why we have special transmitter/reciever combos that work on the 2.4Ghz band instead (plays major havoc with Bluetooth and WiFi)

      So we are safe... for now...

  • Easy to get (Score:5, Informative)

    by lachlan76 ( 770870 ) on Friday January 07, 2005 @02:06AM (#11285469)
    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.

    • Re:Easy to get (Score:3, Informative)

      by Atrax ( 249401 )
      like this one? [jaycar.com.au]
      • Yeah, I'm an Aussie, that happened to be the particular one I was thinking of.

        I've never built that one, although I managed to fuck up another one...however, it still has a use: jamming tv ;)

    • Re:Easy to get (Score:4, Informative)

      by Rick.C ( 626083 ) on Friday January 07, 2005 @01:28PM (#11289593)
      Just look in the DIY kit section of any electronics store

      You might want to look at the specs before you buy one. Check the distortion and channel separation numbers. Is it even stereo? (Many of the cheaper kits are mono. A single electret mic is a clue, here.) Is it PLL controlled or will the output frequency drift all over the place?

      I built the MPX96 [northcountryradio.com] and I've been happy with it for about two years.

      The range is about 200 feet (1/2 mile with a longer antenna - oops!) and the sound quality is "good" - that's somewhere between "fair" and "great".

  • Correction to article.. (Score:2, Funny)

    by Anonymous Coward
    should read..

    " ...that covered my whole block the first time I plugged this product on Slashdot."

  • Slashvertisement (Score:5, Interesting)

    by ingsocsoc ( 807544 ) on Friday January 07, 2005 @02:08AM (#11285483)
    All the images on the linked page are exactly the same as the site selling them.

    • Re:Slashvertisement (Score:5, Informative)

      by Bruce Perens ( 3872 ) <bruce@perens.com> on Friday January 07, 2005 @07:10AM (#11286341) Homepage Journal
      The images are served by the sales site, that was the easy way to get them. The text is my personal review. I don't have a relationship with the manufacturer other than that I purchased the device.

      Bruce

  • My local electronics store... (Score:5, Interesting)

    by Atrax ( 249401 ) on Friday January 07, 2005 @02:09AM (#11285485) Homepage Journal
    ... has similar stuff - like this [jaycar.com.au]. 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

    • Re:My local electronics store... (Score:4, Interesting)

      by lachlan76 ( 770870 ) on Friday January 07, 2005 @02:13AM (#11285508)
      Yeah, you've gotta love Jaycar, they've got so much stuff...i could make a small BAC tester from stuff there if I wanted to.

      Anyway, anyone who is looking for FM transmitters, they have a few models, one of whch has up to 2km range (apparently...I haven't built one). You will have to modify it to take line level input though, they use an electret microphone.

      And also: they have very cheap peltiers.

      I don't know how good they are though, can anyone who has bought one give me an idea of the quality?

  • this sounds nice, but what happens (Score:5, Interesting)

    by Interfacer ( 560564 ) on Friday January 07, 2005 @02:10AM (#11285492)
    if lots of people in the same block start using this?

    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 .at least in europe it is almost completely filled up in the range that all commercial receivers use.

    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.
    • Believe it or not, there are free slots because adjacent broadcast transmitters don't share the same frequency. Certainly for very low power stuff, using the adjacent broadcast transmitter's frequency, as opposed to your local one wouldn't be a problem unless you live in an area equidistant between the two transmitters where some people use one or the other.

      I'm in absolute agreement over Deutsche Shlaeger Zangers though.

    • As i have written in another post, These things are illegal in the UK (we have to use special transmitter/recievers that work on the 2.4Ghz band). So thank god, I dont need to listen to "Johny next door", who loves to broadcast crappy songs, drowning out my regular channels.
    • I don't see any problems using this sort of device in a place such as Australia, at any given place you are lucky to have more then 7 FM stations.

  • Come on people (Score:4, Funny)

    by Neil Blender ( 555885 ) <neilblender@gmail.com> on Friday January 07, 2005 @02:10AM (#11285494)
    Didn't we all learn our lesson from "Pump up the Volume"?

  • Or... (Score:3, Funny)

    by Tickle Cricket ( 845932 ) on Friday January 07, 2005 @02:13AM (#11285506)
    you could just turn your speakers all the way up.

  • Station Content (Score:5, Funny)

    by halcyon1234 ( 834388 ) <halcyon1234@hotmail.com> on Friday January 07, 2005 @02:17AM (#11285527) Journal
    If you play music, can the RIAA sue the air for abetting the distribution of copyrighted material?

  • Receiver? (Score:2, Insightful)

    by fstrauss ( 78250 )
    So what kinda receiver do you carry around that's more convenient than an ipod?

  • Pirate radio (Score:4, Insightful)

    by Epsillon ( 608775 ) on Friday January 07, 2005 @02:22AM (#11285549) Journal
    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.

    • Re:Pirate radio (Score:5, Informative)

      by Bruce Perens ( 3872 ) <bruce@perens.com> on Friday January 07, 2005 @07:07AM (#11286333) Homepage Journal
      It's legal under Part 15 of the FCC regulations as long as you stay under maximum radiation restrictions.

      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

  • Harmonics and aviation bands (Score:5, Interesting)

    by Zachary Kessin ( 1372 ) <zkessin@gmail.com> on Friday January 07, 2005 @02:25AM (#11285562) Homepage Journal
    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.
    • Great strategy: This radio interference is endangering planes so let's strike - which will..er..endager planes so they'll have to stop flying, or fly on with reduced ATC personnel or perhaps management in charge which might..er..increase the risk of danger to the planes.
      • Well its the standard Israeli response to anything, strike. (Don't get me started). It was a case in which the only way that the controllers felt that they could get their point across was by shutting down the airport for a day. I'm not sure if they did.

        It didn't help that one of the Members of our Parlament from a party that runs many of these stations was sugesting that they should broadcast from the Knesset offices so that they won't be shut down.

  • 100mw is NOT what's allowed by law. (Score:5, Informative)

    by djplurvert ( 737910 ) on Friday January 07, 2005 @02:25AM (#11285564)
    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 [fcc.gov].


    • I got all excited there for a second with visions of covering downtown with some good, commercial free music. 100mw and a short feed to a good antenna on the roof of my building would have done the trick for many blocks around me.

      I looked into a 'real' low power FM setup and it seems you have to be a 501C3 religious or educational organization, can't use directional antennas, can't look funny at people on the street, can't name your cat Morris, have to blow the FCC OO, and that was just the rules for t
      • Yes, in fact, "low power FM" is NOT really available to individuals. Look for information on micropower FM. Micropower is the term typically used for part 15 unlicensed transmission. You can cover a few blocks LEGALLY without a lot of cost in some circumstances.

        You can own up to six part fifteen transmitters by fcc rules. What some people are doing is using multiple transmitters fed with the same audio signal.

        I'm surprised that slashdotters aren't very aware of the issues of micropower broadcasting as i
    • You can, in fact, use any amount of power you want. That is, as long as you don't excced [blah blah blah...] that translates to roughly 10 to 20 mw.

      Hey Dad, is that you?

    • Re:100mw is NOT what's allowed by law. (Score:4, Informative)

      by Bruce Perens ( 3872 ) <bruce@perens.com> on Friday January 07, 2005 @07:21AM (#11286371) Homepage Journal
      You're right, the rules have changed, and 250 microvolts per meter at 3 meters seems to be the new standard.

      Bruce

      • Any ideas on a suitable attenuator? I would imagine that you can attenuate the 100mW output down to 20 or 30, and bring it within limits. According to the FCC link in the grandparent, the FCC seems to be concerned more with your transmitter having a range of 200 feet or less, regardless of output power or antenna design.

  • I'd like the 2 watt version (Score:5, Funny)

    by eric76 ( 679787 ) on Friday January 07, 2005 @02:25AM (#11285565)
    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.
    • I used jockey a snow cat grooming snow late at night in the Sierras, and I had my choice of precisely two stations as well. One was rock and the other was roll. I'd have killed for an iPod then.

  • Convoy! (Score:3, Funny)

    by redled ( 10595 ) on Friday January 07, 2005 @02:26AM (#11285568)
    We got a great big convoy...
  • If I was to buy the 2 Watt model [fmtv.us] and the antenna [fmtv.us]...

    1. What kind of range could I expect from this combination? I have 15 acres and would love to have my entire MP3 playlist running rather than just my favorite 512MB from my flash-based player while I mow the lawn.

    2. With it cranked up to maximum power, would I be likely to recieve a visit from the FCC? I'm about 25 miles from the nearest city and there are very few radio stations that come in out here, so I'm not likely to step on someone else's freque
    • To answer question 3, using the page linked in an above post: (http://www.fcc.gov/mb/audio/lowpwr.html#PART)

      PENALTIES FOR OPERATION WITHOUT A PERMIT OR LICENSE
      ...

      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
    • Just because you can't hear it doesn't mean you aren't interfering with others. The FCC has monitoring stations throughout the U.S.

      Using two watts might just net your a visit.

    • Re:A few questions for those knowledgable about ra (Score:4, Informative)

      by Anonymous Coward on Friday January 07, 2005 @02:47AM (#11285647)
      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!)
    • For (1), check out this very recent /. article [slashdot.org]. 40.6uW gets you 546.8 miles. Admittedly that's only a beacon station and not going for anything complicated like FM, but even so your signal could be going a lot further than you expect.

      Which kind of ties in to point (2). "If you build it, they will come." The point isn't that no-one else happens to be using the frequencies, the point is that you're using a regulated resource (EM bandwidth) and if one person gets away with it then everyone will have a go.

  • Pricey (Score:3, Informative)

    by mako1138 ( 837520 ) on Friday January 07, 2005 @02:30AM (#11285578)
    Going to the store page [fmtv.us] 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 [epanorama.net] that are relatively simple and powerful. DIY; save your money and your honor.
  • I bought the CCrane transmitter http://www.ccrane.com/fm-transmitter.aspx/ [ccrane.com] and perfomed the easy mod http://www.xmfan.com/viewtopic.php?t=3257&postdays =0&postorder=asc&start=0/ [xmfan.com] to increase it's output power.

    It works great and covers the entire house. It's cheaper than the original post and includes a case and power supply (problems that the original poster had with the ebay one).

  • Beware of cheap FM transmitters (Score:5, Informative)

    by Okian Warrior ( 537106 ) on Friday January 07, 2005 @02:50AM (#11285658) Homepage Journal
    Beware of cheap FM transmitters for this purpose: the majority of them are no good.

    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.

  • Somebody didn't read the FCC regs (Score:4, Informative)

    by DaCool42 ( 525559 ) on Friday January 07, 2005 @03:00AM (#11285682) Homepage
    On FM frequencies, these devices are limited to an effective service range of approximately 200 feet (61 meters).

    source:
    http://www.fcc.gov/mb/audio/lowpwr.html [fcc.gov]
    see also:
    http://www.fcc.gov/Bureaus/Engineering_Technology/ Documents/bulletins/oet63/oet63rev.pdf [fcc.gov]

    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.

  • This seems to be asking for trouble (Score:4, Insightful)

    by gabebear ( 251933 ) on Friday January 07, 2005 @03:09AM (#11285709) Homepage Journal
    If you just want a radio station in your home it would seem to make more sense to use a Carrier Current [fcc.gov] 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 [northcountryradio.com].

    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.

  • FCC Approval (Score:3, Insightful)

    by femto ( 459605 ) on Friday January 07, 2005 @03:13AM (#11285719) Homepage
    As mentioned here [technocrat.net], the unit is not FCC approved. Once this guy comes onto the radar (by a slashdotting, for example) he might well get a call from the FCC.
    • Part 15 devices DO NOT have to be FCC approved. That is, if you are going to use them for unlicensed part 15 operation, as the original author thinks that he is, then no FCC approval is required.

      The issue ISN'T the fcc approval. The issue is the misundertanding of the part 15 emmisision requirements for the FM broadcast band. 300mw is not allowed, neither (in most cases) is 100mw.

      The issue of fcc approval is ONLY an issue if you intend to obtain an fcc low power broadcast license which is not available to

  • In Europe these would be illegal. (Score:4, Informative)

    by Serious Simon ( 701084 ) on Friday January 07, 2005 @03:15AM (#11285727)
    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.
    • ... a few weeks ago, my nephew showed his Ipod FM transmitter he got with him from the States. It's quite neat, and the power is low enough not to disturb your neighbours' radio. But, in The Netherlands it's not allowed (though I don't see how the 'radio controle dienst' (dutch FCC) will find out about it, as people mostly use it in cars.

      In other news, frequencies for radio-transmitters in the FM-range where auctioned last year for a few billion euro's. In the end, it's all a money thing.

  • User-controlled audio stations (Score:4, Interesting)

    by mcbridematt ( 544099 ) on Friday January 07, 2005 @03:19AM (#11285740) Homepage Journal
    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.
  • From the photo, the circuit board looks to be no better than prototype quality. It doesn't even have a soldermask, let alone silkscreening. The layout seems rather inelegant, as well. For $140, one has the right to expect a well-designed, commercial-quality PCB. This one clearly is not.

  • Amazing prices (Score:3, Interesting)

    by milosoftware ( 654147 ) on Friday January 07, 2005 @04:22AM (#11285908) Homepage
    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.
  • 100mw is NOT going to be OK with the FCC. 10mw is enough to get busted.

    To comply with the unlicensed rules, you need to turn that thing down by a couple orders of magnitude. The lower limit isn't actually in watts, it's actually something like 85uv @ 3 meters. I don't recall exactly, but it's not my ass on the line here... go read the rules before yous gets busted. :-)

    To comply with the licensed rules (you said you don't wanna lose your ham license), you need to start broadcasting your call sign peri

    • Well.

      1) As I have ALREADY stated, it's 250uv/meter at three meters.

      2) Licensed hams, like everybody else, can use part 15 rules to transmit if desired. Further, since there is no such thing as part 97 (ham radio) transmission in the FM broadcast band there is NO need to transmit one's license or restrict themselves from playing music.

  • Since we are all talking about getting busted and such I thought I might mention Free Radio Santa Cruz which has been around for over 10 years. They were just recently busted and the FCC just shut them down. You are not gonna get busted by the FCC if you do this. If the FCC wants to bust you they must come to the place first and notify you to stop. If you do not stop they can come in and take your equipment . I have never heard of anyone going to court ever. We need more community radio stations with m

  • Great for parties! (Score:4, Interesting)

    by duffster ( 787023 ) on Friday January 07, 2005 @05:59AM (#11286115)
    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.

  • It amazes me... (Score:3, Interesting)

    by Anita Coney ( 648748 ) on Friday January 07, 2005 @09:00AM (#11286814) Homepage
    Than when the topic is P2P everyone either says it's "fair use" or even if it is illegal, you're chances of getting caught are so small it's never going to stop it anyway.

    But when the topic is FM transmitter, suddenly everyone comes out of the wood work and posts about the illegality of the situation.

    Let's set the record straight. The FCC will shut down your station, if and only if, a broadcaster complains. And because anyone smart enough to set up their own FM transmitter is smart enough to choose a frequency not already occupied by a local station, the FCC will never shut them down. Never.

    I know a group of people who run a pirate station which transmits over 20 miles and have run it since the early 90s. At one time the FCC got a complaint from a local station, the FCC investigated, found it didn't really interfere, and so it did nothing.

  • Cool (Score:4, Insightful)

    by hey! ( 33014 ) on Friday January 07, 2005 @10:10AM (#11287329) Homepage Journal
    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.

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