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Antenna advice please

Discussion in 'Electronic Basics' started by Eric R Snow, Sep 10, 2005.

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  1. Eric R Snow

    Eric R Snow Guest

    I'm sure this is a pretty basic question. Which is good because my
    knowledge of electonics is pretty basic. 30 years ago I bought a CB
    radio, antenna, and an SWR meter. I believe SWR stands for Standing
    Wave Ratio. Anyway, this meter was for matching the antenna to the
    radio. Changing the position of the antenna on the car would affect
    the match. Now, I have an FM transmitter that I bought as a kit from
    Ramsey. It works well with included telescoping antenna. As long as
    the radio is within about 80 feet. The transmitter is used to listen
    on the radio to stations broadcasting on the web. The location of the
    antenna is pretty close to the center of a 10 acre parcel that is
    about 1000 feet long by 450 feet wide. The ideal antenna would be one
    that broadcasts in a rectangle of the same proportions so as not to
    break any FCC rules.So what I would like are pointers to likely
    antennas and how to build the SWR meter. I've googled but haven't been
    able to find something simple enough for me to understand. Any ideas
    are very welcome. I'm a machinist with many years experience so if
    anyone has any metalworking questions I'd be happy to try to come up
    with a good answer.
    Eric R Snow,
    E T Precision Machine
  2. PN2222A

    PN2222A Guest

    Well, good luck on that one. Easier to arrange for it to rain
    only on 1/2 of your lot!
    Unfortunately, modding the transmitter or the antenna will
    violate the part 15 rules for this device.
    Extending the range from 80 feet to 330 feet will require more
    power. Which won't be within the regs.
    Sorry, Eric. Your transmitter doesn't produce enough
    power to move the needle on any SWR bridge (passive) that you
    can build.

    The good news is that there's no real benefit to matching the antenna
    and line on a tiny TX like this.


    Let me introduce my partner,
  3. Eric R Snow

    Eric R Snow Guest

    The instructions from Ramsey state that other antennas can be used
    with this transmitter without violating FCC rules. Most important is
    to keep the signal within my property.
  4. John - KD5YI

    John - KD5YI Guest

    Most important is found in paragraph (b) below. This means you can use any
    antenna you like, as long as your field strength (in any direction) does not
    exceed the value specified below.

    [Code of Federal Regulations]
    [Title 47, Volume 1]
    [Revised as of October 1, 2004]
    From the U.S. Government Printing Office via GPO Access
    [CITE: 47CFR15.239]

    [Page 816-817]



    PART 15_RADIO FREQUENCY DEVICES--Table of Contents

    Subpart C_Intentional Radiators

    Sec. 15.239 Operation in the band 88-108 MHz.

    (a) Emissions from the intentional radiator shall be confined within
    a band 200 kHz wide centered on the operating frequency. The 200 kHz
    band shall lie wholly within the frequency range of 88-108 MHz.
    (b) The field strength of any emissions within the permitted 200 kHz
    band shall not exceed 250 microvolts/meter at 3 meters. The emission
    limit in this paragraph is based on measurement instrumentation
    employing an average detector. The provisions in Sec. 15.35 for
    limiting peak emissions apply.
  5. Eric R Snow

    Eric R Snow Guest

    Greetings John,
    Of course you're correct. The FCC can't use the size of a piece of
    land as a gauge. And I seem to recall reading that even if the power
    does not exceed the above it must still not interfere with someone
    else recieving radio signals.
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