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Technology

Microwave/High Frequency Private Broadcasting? 18

Posted by Cliff from the applications-for-new-tech dept.
eutychus is curious about the following: "I'm interested in high-frequency broadcast and directed radio (similar to what high-frequency cordless phones do). I know of cordless phones which get ~3mi radius, and I'm looking for a way to do at least that. There are several applications for this. 1) Private radio station for MP3's (have a transmitter using my outdoor antenna broadcasting from my PC's CD changer and CD's converted to MP3. Allow song selection via phone, web, or radio remote, and retransmit at microwatts over FM to the car's radio). 2) Data connection / wireless network between homes & offices... best if you could do both voice and data over it and 3) X10 control from your PC over long distances. These are a few examples, but the possibilities are limitless. Does anyone have any details on regulations, or a starting place on building something like this? " Good ideas, but I'm sure there are better ones that could be achieved with this technology. Any suggestions on getting it started?
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Microwave/High Frequency Private Broadcasting? More

Microwave/High Frequency Private Broadcasting?

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  • First thing to do would be to check with the F.C.C. (assuming you're in U.S.ofA.)who will probably tell you that there aren't any fequencies up there legally available for what you want to do, but ask them if the experimental band between 160kHz and 190kHz is still available. A few component changes to the front end of an old AM car radio will give you a receiver to use in initial design and testing.

  • If you Become a amateur radio operator (HAM), you'll be able to legally broadcast on most frequenties (HF, VHF, UHF). You'll even be able to try out radio tv, and satellite transmissions!

    To become a HAM, you'll need to pass the FCC exam, then you'll get a license that will cost you about $30 a year. You can get more infos on Yahoo! [yahoo.com] or at this HAM-HOWTO site [irony.com].

    GFK's

  • hmm, sounds interesting... do you know if I could possibly broadcast a few mbps ethernet link at least 5 miles if I become licensed?
  • I believe you'll find that the sub radios work not in the kiloHertz range but in the Hertz range. Infrasonic. E.L.F. This is all from distant memory, by the way.

  • I know that certain microwave frequencies can be used by the public for this purpose. I have worked with several LAN/WAN links between 1-5mbps over several miles. I think they are in the 2ghz and 40ghz ranges, but I really don't know a whole lot about this... as is why I posted the article.

    BTW... they were PtP (point to point) links, not broadcast... i.e. dishes tuned and pointed directly at each other. Depending on your use, this could be a crucial factor.
  • ouch, that'll hurt... I was hoping to hook my friend into my local network using wireless technology, but I don't think I can point a dish at another one when they're 5 miles apart.
  • "If it is an electron and vibrates, there is a rule for it." That's great, can I steal it?

  • I know nothing of wireless and RF, but have you investigated 802.11 (wireless ethernet) ? For voice/audio application, you coud do VoIP and streaming audio, and since this is broadcast (not sure... ought to verify), you could connect all the friend of your neighborhood to your LAN for some wireless Quake.

    As I said, I don't know much about about wireless in general and 802.11 in particuliar, so don't take my word for it.
  • FCC regultions specifically prohibit the use of amateur radio frequencies for the use of broadcasting. Or conducting business. Amateur radio is centered around public service and advancing the radio art.

    If you think you will get away with it, there are hams who have made it a hobby tracking down illegal sources of RF emission.

    However, the FCC does allow other non-amateur frequencies for the purposes you mention. The CFR (code of federal regulations) Title 47 part 15 tells you what is available. There are frequencies at 1.9GHz, 2.4GHz, 5.5GHz that you could possibly use for the aforementioned purposes. However, you will need (and want) to use spread spectrum modulation. Also, you are only allowed one watt of transmitted power. They do not want you interfering with other Government agencies already using these frequencies for other purposes. While Scully and Mulder will not come knocking on your door, their buddies will, wanting to know why you're interfering with their local radionavigation beacons. You will not believe how picky they can be.

    You will see what I mean as you read over the rules and regs. If it is an electron and vibrates, there is a rule for it. Up to 300 GHz, which by my calculations is where you find heat, and of course the visible spectrum after that.

    www.fcc.gov [fcc.gov] is the place to start if you want more details. I have to hand it to them, they have done good job at putting the CFR online. BTW, part 97 covers amateur radio operations so you can take a look at them too.

    Besides the regulations, microwaves are technically challenging. While the challenge is interesting to many in the amateur radio community, historically there has not been alot of 'plug and go' solutions for microwaves. It was always a 'roll your own' kind of proposition. I thought it more plumbing with some of the fancy waveguides around. However, there is a lot of surplus stuff that is hitting the market now so that will change.

    Distance wise, I think you will max out at 3 miles. with clever receiver and antenna design you could do 10 miles. Just hope it doesn't snow, as water is very asorbant to these particular frequencies. (also another reason for low power, what is your body made up of???).

    My personal choice if I were you would be light communications. You can have all the bandwith you could want and be a pioneer at the same time. While coventional wisdom suggests that this would not be very reliable, recent product offerings by Lucent technologies suggest that there may be ways around them. It would be interesting to try, lots of room for experimentation, economical, and straightforward to do.

    Phill Kennedy NA7E
  • At the 160 KHz band your MP3s or other high speed digital modes won't work. First, your a Nyquist bust because your stream is going to be at least 56K and the band is only 30K wide. It might be used for long distance low rate paging though. Also, BPSK (binary phase shift keying) is a possibility for low speed messaging. Second, if you tranmit anyway you're whacking out everybody's AM radio (from guaranteed harmonics). Contrary to what you might think, people still do listen to AM. Those seniors down at the center love their Paul Harvey at noon. See my post below for alternatives.

    Another reason it won't work is just wait 'til your neighbor switches on their flourescent light dimmer. DOH!!!!! There goes the band!!!! What a bust for that MP3 stream!

    There is a group of radio amateurs who call themselves "lowfers" who like to play with these frequencies. Do a web search on the term. Technically and historically interesting, their newsletter is called the 'lowdown'.

    Other groups who look to these frequencies are spelunkers who want to phone home when they get stuck in a hole, and the navy to reach underwater subs with nuke aiming info.
  • To become a amateur Radio operator the local club may charge a maximum of $6.49, adjusted by the FCC anually using the CPI, to cover out of pocket expenses. This is an optional fee however, and I believe some clubs give it for free. The license is good for 10 years, and renewal (no examination required) is free.

    You can't broadcast music using an amateur radio license however. See above post.
  • >You can't broadcast music using an amateur radio license however. See above post.

    I don't know if you could get around it by calling MP3s DATA files, instead of music. Or what if you used a weak cypher? How about if you transmitted "All Country, All The Time", nobody in his right mind would call THAT music.

    While I'm at it, I'd like to see digital radio stations go on the air. Imgine being able to capture that digital signal and compressit to MP3 while you sit and listen. (BTW, I don't see this as being any different than using an audio tape to record radio broadcasts)

    Would it be a violation of FCC rules to adapt cordless phones to do this?

    LK
  • It seems thet now there is a public use band around 2.4 GHz, for low power radio devices (here in EU,
    Moreover, I think that the X10 people are selling some devices that use this band to send DVD Video/MP3 Audio from the computer to the stereo/home theatre.
  • I know of cordless phones which get ~3mi radius

    I'd really like to try one of these. Does anyone know any models/manufacturers?

  • I don't know if you could get around it by calling MP3s DATA files, instead of music. Or what if you used a weak cypher? How about if you transmitted "All Country, All The Time", nobody in his right mind would call THAT music.

    No, (at least in Canada) you cannot broadcast anything; by broadcasting, I mean always sending something to anyone. Also you cannot encrypt what you send in the air; the police had to ask for special permissions to do this. Even more, a couple of years ago (I don't know if it's still applicable) you could not talk in another language than the 2 officials in Canada (French & English), this was considered as 'encryption'...

    GFK's
  • People complain about US crypto export laws. If you're not BSing me, Canada is even more ass backwards on Crypto than is Uncle Sam.

    So what you're telling me in Canada, German is a form of Crypto?

    But anyway, I think that we were talking about the US because of someone bringing up the FCC.

    LK
  • I don't think I can point a dish at another one when they're 5 miles apart.

    Why not? Buy/borrow a GPS. That will at least get you close, and then adjust the dishes to maximize signal level. Of course, with GHz frequencies, you better be going from hilltop to hilltop because line of sight will be important.

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