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Someone explain radios to me...

Discussion in 'Technical Chat' started by iJDub, Apr 17, 2013.

  1. Apr 17, 2013 at 7:23 PM
    #1
    iJDub

    iJDub [OP] Well-Known Member

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    OK, so CB radios operate in the 27MHz range...

    GMRS operates in the 460MHz range...

    HAM operates here mainly in the 144-148Mhz & 430-450Mhz range...

    Why can't there be 1 radio to operate in ALL these ranges?

    Is it just a FCC regulation? Why do I need to buy 3 radios? lol
     
  2. Apr 17, 2013 at 7:27 PM
    #2
    zbaldo

    zbaldo Well-Known Member

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    Duct tape three together and voila. Jk I am interested as well
     
  3. Apr 17, 2013 at 7:55 PM
    #3
    Turbomeister

    Turbomeister That One Guy

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    I think someone more knowledgeable than me should chime in, but I'll contribute my small amount of experience as a ham radio operator.

    You can easily receive all three bands on one radio. In fact, nearly all VHF ham radio transceivers have the capability to listen on all these bands, as do most scanners.

    I think in your question though, you meant transmit. That one is a little more tricky. There is no technical reason one box couldn't contain the tuner and related circuits to transmit FM on 144-148/440-450 MHz for ham, AM around 27MHz for CB, and FM around 460MHz for GMRS. On the legal side of things, I don't know of any FCC regulation preventing this either, but I could be wrong.

    With any such unit though, the buyer would have to possess both a amateur radio license and a GMRS license to use it. (CB is the only service you mentioned that doesn't require licensing to transmit on) It seems to me the issue is more about sales. How big of a market is there really for individuals who have both licenses mentioned and still want to transmit on CB also? My guess is not very big. Most people are really into one service or another, not all at once. So because it isn't profitable to sell, it isn't made! And if you just want to listen, not transmit, most scanners on the market, as well as most VHF ham radios, would achieve that.

    If you want to build it and sell it though, be my guest! I'll even be your first customer! ;)

    Hopefully someone with some more knowledge than me will chime in next though and clarify a little....I'm sure my ramblings are hard to read :p
     
  4. Apr 17, 2013 at 10:10 PM
    #4
    Rich91710

    Rich91710 Well-Known Member

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    Transmitter and antenna tuning.

    The optimal length for the antenna is a factor of the wavelength, which is inversely proportional to the frequency.

    Short story... high frequency, small antenna, low frequency, large antenna (like the 722ft half-wave antenna used for 640Khz).

    The actual formula is 3x10^8 (speed of light in meters/second) divided by the frequency.
    100Mhz has a wavelength of 3 meters, so a half-wave antenna would be a hair under 5ft tall. CB antennae are typically quarter wave (3x10^8/27*10^6 = 11 meters /4 = about 9ft).

    Theoretically, the same whip could be used as a quarter wave CB antenna, half wave for a 54Mhz signal, and full wave for a 108Mhz signal..... but the electronics in the radio are completely different.
    It's not impossible to make a multiband transmitter, but the power amplifier section would literally be 3 separate units fed by one preamp.

    But 144-148, 430-450, and 460 are uneven multiples of a common number, and thus, would not be able to use the same antenna. The 144-148 range is 1/3rd of the 430-450 range... and 460 would be badly out of tune on an antenna tuned center on 440 for the 430-450 range.

    Theoretically, 430-450 could tune on a 27Mhz whip... a quarter wave CB antenna would be 4x the length needed for a full-wave 430-450 antenna.
     
  5. Apr 17, 2013 at 10:50 PM
    #5
    iJDub

    iJDub [OP] Well-Known Member

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    You lost me at transmitter :)

    Question, I am looking at a ICOM GMRS radio that can transmit/receive 450-512 MHz range...what antenna do I need?

    If I get a Cobra 29 for my CB...what antenna would I need for that? Possible to share one for both radios?
     
  6. Apr 17, 2013 at 10:52 PM
    #6
    95 taco

    95 taco Redneck rich

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    for the cb, firestiks get alot of good votes, when i install mine i'm gonna go with a steel whip so i don't have to tune it.

    http://www.firestik.com
     
  7. Apr 17, 2013 at 10:54 PM
    #7
    MonkeyProof

    MonkeyProof Power Top

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    You would still have to tune a steel whip..
     
  8. Apr 17, 2013 at 10:56 PM
    #8
    95 taco

    95 taco Redneck rich

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    even if it's a true 1/4 wave?

    EDIT: i found this from a earlier thread
     
    Last edited: Apr 17, 2013
  9. Apr 17, 2013 at 11:06 PM
    #9
    iJDub

    iJDub [OP] Well-Known Member

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    What about for the 450-512 MHz GMRS radio?
     
  10. Apr 17, 2013 at 11:12 PM
    #10
    MonkeyProof

    MonkeyProof Power Top

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    Those are fixed antennas built into the unit itself.
     
  11. Apr 21, 2013 at 9:55 AM
    #11
    n1dp

    n1dp Member

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    Amateur Radio sets are Type Approved by the FCC differently than radios for CB or GRMS. You can use "commercial" type rated radios programmed for Amateur frequencies, but not legal to use an Amateur set outside of the Amateur bands.

    Amateur Radio has unique privileges within their bands. Their radios are allowed to be "frequency agile;" that is to say you can select any frequency in the radio. Commercial radios and special service radios such as CB and GRMS usually have radios that are channelized.

    You can use a UHF commercial radio to program and transmit both 70cm (420-450 MHz) and the GMRS frequencies. Each frequency programmed must meet the various regs/band plans. They do not program on they fly; it must be pre-programmed.

    As mentioned before, it is impractical to make an antenna for such a wide range of frequencies. You never want to "share" an antenna between two transmitters because you will feed RF power into the output of the other radio.

    Other than amateur radio sets and some aircraft or military applications, you will not see any multi band radios. Even then, by using automatic antenna switching, they still need to switch antennas.
     
  12. Apr 21, 2013 at 10:58 AM
    #12
    iJDub

    iJDub [OP] Well-Known Member

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    So the ICOM Radio 6201 that I am looking at which uses the 450-512 MHz range...what kind of antenna woud use? I'm intereste in that radio as I can use the GMRS 462 an 467 MHz range. There's also some police channels that I'd like to be able to listen to in he 484 and 506 MHz range.

    What do I need to do?

    I'll run a seperate antenna / radio or CB.
     
  13. Apr 21, 2013 at 1:28 PM
    #13
    kai38`

    kai38` Well-Known Member

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    There is an illegal but simple mod for HAM radios to allow you to use the HAM and talk on the GMSR channels.
    Google it if interested.
     
  14. Apr 21, 2013 at 7:52 PM
    #14
    n1dp

    n1dp Member

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    Go to HRO.com. Ham Radio Outlet carries antennas for, or can be used on the 460 band. If you are listening only and not transmitting on the other frequencies, 484 and 506 MHz, it will receive just fine.
     
  15. Apr 21, 2013 at 8:11 PM
    #15
    iJDub

    iJDub [OP] Well-Known Member

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    Yeah 484 and 506 just listening lol wouldn't want to transmit.
     
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