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VHF Remote Radio Questions

Discussion in 'Electronic Basics' started by Kitchen Man, Jul 30, 2005.

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  1. Kitchen Man

    Kitchen Man Guest

    Howdy all,

    I want to move a base station of a mobile radio system to a remote
    location where I hope to get better coverage, but I want to keep the
    mic and channel control in the present location. I have access to
    either an RS-232 or a DS0 line, whichever I wish to use, and the line
    length is less than 10 miles. The frequencies are currently allocated
    and on the air, so there are no problems with the bureaucracy. I have
    been researching VHF modems, but am unclear about design applications.
    Our present transmitter is operating at 50W. I was hoping for a
    little insight about how to go about setting up this system, and
    possibly some recommendations about what equipment offers the best
    option for implementing this type of a setup. I need to implement a
    selectable two-channel system. Thanks for your time and suggestions.
     
  2. Fred Abse

    Fred Abse Guest

    I think you'll find that the base station location is specified on the
    license. I don't think there's a jurisdiction in the world that will let
    you relocate without proper authorization. It's all part of frequency
    use planning. They might well want a frequency change for the new location.


    I have
    You need a leased voice frequency line, a proper controller at the office
    end, and proper remote interface equipment at the base station end.
    Alternatively, you might use a UHF or microwave link. This all needs
    approved equipment and is pretty damn' expensive.

    If you need to ask these questions, it suggests to me that you don't know
    enough about what you're trying to do to be competent, or legally
    authorized.

    Consult a properly licensed engineer with the proper knowledge and test
    equipment.
     
  3. Kitchen Man

    Kitchen Man Guest

    Thanks for your concern, but I believe I mentioned that any
    bureaucratic hurdles should not be a problem.
    As I mentioned, I can use either a DS0 or an RS-232 line, both of
    which exist and are available for the project. Microwave and UHF are
    out, as there is no line of sight. This is why I did not mention
    those alternatives. "Proper" equipment is the reason I made the post;
    I was hoping someone with specific knowledge could point me to same.
    Your answers suggest to me that you would rather preach than offer
    assistance. Have you never met an engineer who needed help with a
    technical task? The fact that I need to ask these questions only
    points out a lack of specific familiarity with specific equipment.
    All's well. I believe that I have dreamed up a solution while camping
    out this weekend. Kind of how a properly licensed engineer might
    solve a problem - throw out feelers for suggestions, then ponder the
    problem while relaxing a bit on holiday. The fending off of
    unconstructive criticisms is all part of the day's work, I suppose.

    Thanks anyway. Oh, and I do have a bit of TE lying about. No
    worries, mate.
     
  4. Don Bowey

    Don Bowey Guest

    I may be able to help, but I need you to define what you call a DS0. DS0 is
    only a 64kbit/s capability or capacity. Are you trying to say you have a
    channel in a digital facility available to you? If so, what type of channel
    unit does it have? What are the characteristics of the voice frequency
    interfaces to the TX and RX and how is the TX currently keyed?

    Don
     
  5. Kitchen Man

    Kitchen Man Guest

    You and I are defining DS0 in the same way. I don't know the
    specifics of the particular line, I've only been told that it's
    availible for use if I can use it. As I mentioned in another
    newsgroup, this is a low-priority project, almost a spare-time
    activity. I will investigate the characteristics of the line in the
    next few days. Thanks for your questions. Some further info:

    The radio is a Kenwood TK-720. Today we mulled the possibility of
    breaking the line at the KMC-18 DTMF mic input, and multiplexing voice
    and a PTT tone onto our transmission line up to the relocated base.
    The drawback is that we won't be able to change channels, but we can
    live with that. We only use two, and we have interesting plans for
    remote access to the other channel (mwahahahaha!). I've also been
    looking at some turn-key solutions from online companies, but that
    would require budget begging, and it would be neat if we can do this
    as an in-house, shoe-string project.

    (Just for clarity, I've started the process for asking for a change on
    the license, although we won't be done with this for some time. Also,
    I have a class 2 FCC license, so I'm allowed to play with the XMTR ;-)

    I'll post again after I've had a chance to investigate our Cisco
    network that supplies the now-empty DS0 line to the top of the hill.
    Thanks again for your input.
     
  6. Don Bowey

    Don Bowey Guest

    If you get a choice of channel unit types, consider an E&M 4-wire unit.
    This will provide total isolation between the transmit and receive paths for
    both the audio and the DC signaling voltages (TX transmit and RX squelch if
    you have that capability. You will need to work up a design to coordinate
    the radio voice interface impedances and levels, and DC signaling with the
    channel unit requirements.

    By the way, the FCC eliminated the 1st and 2nd class licenses. We all hold
    the General Class commercial license now.

    Since you have dtmf capability, you could use that to switch the channel
    freq.

    Good luck

    Don
     
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