Wireless Network Training

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  1. Gain
    • Increase in a RF singnals amplitude.
    • An antenna or amplifier.Gain is measured in dB
  2. Loss
    A decrease in a RF signal amplitude .loss is measured in dB
  3. Reflection
    • When a RF wave strikes a large object
    • Surface of the earth , buildings, or walls
  4. Refraction
    • Bending of RF waves as it passes through something of different density .
    • Ex. passing through fog. this is a serious issuse for long distance
  5. Diffraction
    • When a RF wave bends as it passes around a large object.
    • Ex. Ripples of waves across a pond that go around a boat or stump in the pond.
  6. Scttering
    • When a Rf wave bends as it passes around small objects .
    • Ex. Rocks or sand near the RF path or even heavy dust in the air .
  7. VSWR
    • (Voltage standing wave ratio)
    • Occurs when there is a mismatch in impedance between devices in the RF system . This causes return loss .
    • Think of a large pipe feeding into a smaller pipe . The water from the large pipe will over flow the capacity of the smaller pipe and the water will begin to return , back up the path it came.
  8. Amplification
    Incressing the power of RF signal
  9. Absorption
    • When the RF signal is absorbed by material .
    • Ex. Concrete wall
  10. Free-space path loss
    The loss of RF signal over dispersion . This is natural loss of signal over distance .
  11. Delay spread
    the arrival of the direct singnal and the reflected signal at the receiver
  12. Watt(W)
    One watt is the rate at which work is done when one ampere (A) of current flows through an electrical potential difference of one volt (V).
  13. MilliWatt(mW)
    1/1000 of a Watt.
  14. Decible(dB)
    A relative measurement of power
  15. -3dB
    Divide by two
  16. +3dB
    multiply by 2
  17. -10dB
    Divide by 10
  18. +10dB
    Multiply by 10
  19. A 20 mW signal is transmitted to an amp that adds 10 dB of gain. What is the strength of the output
    20mW * 10=200mw
  20. dBm
    A measure of dB when compared to 1 mw (an absolte value)
  21. dBi
    • A measure of dB when compared to an ideal antenna (an istropic radiator)
    • Ex. The sun is a istropic radiator as it can radiate its energy , perfectly in every direction . Real antennas arent perfect and radiate energy in one direction or another.
  22. dBd
    • a measure of dB , relative to a dipole antenna .
    • This type of antenna has gain of 2.12 dBi .Tus you can convert dBd to dBi by adding 2.14
  23. RSSI
    • Receive signal strength indicator .
    • ( no math measurements)
  24. A 100 mW signal is transmitted from an AP . How many dBm is that?
    • A dBm is db per 1 Mw
    • To take 1 mW and turn it into 100mW ,what do you have to do ?

    1mw* 10*10 =100 mw

    • Each multiple by 10 is 10dB . thus that is 20dB, total.
    • 1mW+20dB=100mW
    • SOO, 100 mW=20dBm
  25. System operating margin (SOM)
    This is caculated by adding together all the gains and losses between the sending and the receiver.
  26. Fade Margin
    Extra signal strength added to the link budget to allow for inconsistent signal .
  27. Intentional Radiator
    Includes all parts of an RF system but NOT the antenna
  28. Equivalent Isotropically Radiated Power(EIRP)
    The RF power radiated by the antenna
  29. The 6dB Rule.
    For each 6dB increase in EIRP, the reange doubled
  30. Visulal line of sight (LoS)
    The apparntly straight line of sight . Apparent because light waves are subject to refraction , diffraction and reflection
  31. RF LoS
    Can be blocked by the fresnel zone ,unline VLoS
  32. Fresnel Zone
    • area around the VLoS
    • 3 dimentual .60 % of the radious of the VLoS
    • Water obsorbs RF signals.
  33. Beamwidths
    the width of the antenna beam ( horizontal and vertical )
  34. Azimuth and Elevation
    • Azimuth is the top down view of an antennas coverage . The Elevation is the side vide of an antennas coverage .

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Wireless Network Training
2012-03-28 18:43:24

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