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Factors affecting signal strength.

  1. Jul 27, 2007 #1
    I have investigation on measuring the factors the signal strength from the transmitting antenna. I have some idea about measuring the signal strength.
    Is it true to use field intensity meter to measure signal strength with the unit of volts per metre? Thank you for helping out.
     
  2. jcsd
  3. Jul 27, 2007 #2

    berkeman

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    Staff: Mentor

    Yes, that is correct. Another common unit of measure for field strength is dBuV/m, when you get farther away from the transmitting antenna, and the field strength is getting weaker.
     
  4. Jul 27, 2007 #3

    xez

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    Well the technical UNIT is V/m, but
    what you'll actually MEASURE at the
    output of a receiving antenna is
    either volts, amps, or power.

    The predetermined geometry and sensitivity specification of the
    calibrated receiving antenna is then
    related to its measured output signal
    and thus one can obtain a V/m value.
     
  5. Jul 28, 2007 #4
    well, what are the factors that affect the signal strength in the transmitting antenna?

    field intensity meter will measure in terms of V/m, right? Thank you so much.
     
  6. Jul 28, 2007 #5

    xez

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    "field intensity meter will measure in terms of V/m, right? Thank you so much."

    Yes, if it's a field strength meter, overall the instrument
    will be able to give you a V/m reading through whatever
    process of use its manual specifies.

    "well, what are the factors that affect the signal strength in the transmitting antenna?"

    Transmitting antennas have a radiation efficiency factor
    that determines how efficiently they radiate. But that's
    mostly relevant from the perspective of the transmitter.

    Energy that the transmitting antenna does NOT radiate
    into the far field is irrelevant to the question of the
    field strength a given transmitting antenna does produce
    at a given distant location.

    It's most appropriate to measure the field strength of
    a transmitting antenna at a distance that is at LEAST
    several wavelengths away from the antenna, and at
    least several times the geometric size of the antenna
    away. This is what's known as the "far field" measurement
    which indicates the field strength the transmitting antenna
    produces at a distant location, and this is representative
    of the propagating wave that is produced by the antenna.

    If you measured the field strength too close to a
    transmitting antenna you would get larger or smaller
    than expected values due to the effect of "near field"
    non-radiating or non-efficiently radiating radiation
    components from the antenna. E.g. even a simple
    LC circuit produces E and M fields NEAR itself, and hence
    a field strength, but it is almost useless as an antenna
    since almost no energy is radiated to distant locations,
    it is all remaining concentrated very close to the
    circuit / antenna.

    So the effects that relate to a far field signal strength
    measurement produced by a transmitting antenna are:

    a) Geometric field pattern of the antenna in the direction(s)
    that cause signal to be receivable at the measurement
    location. The higher the geometric gain of the antenna
    in directions that influence the receiving location, the
    greater the received signal could be there.

    b) Power being radiated by the transmitting antenna;
    the more power being transmitted, the greater the
    remote signal strength.

    d) Obstruction loss between the transmitter and receiver;
    i.e. is there an ocean or mountain in the path of the signal
    that absorbs / reflects a given amount of it? Are there
    obstructions like trees, buildings, etc. These will all cause
    path loss.

    c) Propagation absorbtion loss between the transmitter
    and receiver; is some of the signal absorbed in the air,
    the ionosphere, by the ground, by foliage, by
    rain/clouds/snow, et. al.

    d) Propagation path distance between the transmitter
    and receiver; depending on the path of signal progagation
    there will be some loss due to the geometric diffusion of
    signal energy and hence field strength over that distance.

    e) Multi-path or diffractive signal diminishment at the
    receiving location. It's possible for signals to arrive at
    the receiver from several different paths or reflections.
    In the case of multiple signal paths the signal may not
    'add up' in phase at the receiver and hence the overall
    signal strength may become erratic or weaker at the
    receiver, or in some cases it could be enhanced.
    Obstacles that diffract the transmited wave between
    the tx and rx will cause a diffraction pattern at the
    receiver location and that interference/diffraction will
    affect the signal.
     
  7. Sep 2, 2010 #6
    how can i measure the factors that affects the signal strength from the transmitting antenna?
    how should i start on the investigation? thank you.
     
  8. Sep 2, 2010 #7

    berkeman

    User Avatar

    Staff: Mentor

    What have you learned by reading this old thread? Surely it must have given you some ideas on how to proceed?
     
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