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Gain
- Increase in a RF singnals amplitude.
- An antenna or amplifier.Gain is measured in dB
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Loss
A decrease in a RF signal amplitude .loss is measured in dB
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Reflection
- When a RF wave strikes a large object
- Surface of the earth , buildings, or walls
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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
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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.
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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 .
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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.
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Amplification
Incressing the power of RF signal
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Absorption
- When the RF signal is absorbed by material .
- Ex. Concrete wall
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Free-space path loss
The loss of RF signal over dispersion . This is natural loss of signal over distance .
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Delay spread
the arrival of the direct singnal and the reflected signal at the receiver
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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).
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MilliWatt(mW)
1/1000 of a Watt.
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Decible(dB)
A relative measurement of power
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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
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dBm
A measure of dB when compared to 1 mw (an absolte value)
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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.
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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
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RSSI
- Receive signal strength indicator .
- ( no math measurements)
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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
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System operating margin (SOM)
This is caculated by adding together all the gains and losses between the sending and the receiver.
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Fade Margin
Extra signal strength added to the link budget to allow for inconsistent signal .
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Intentional Radiator
Includes all parts of an RF system but NOT the antenna
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Equivalent Isotropically Radiated Power(EIRP)
The RF power radiated by the antenna
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The 6dB Rule.
For each 6dB increase in EIRP, the reange doubled
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Visulal line of sight (LoS)
The apparntly straight line of sight . Apparent because light waves are subject to refraction , diffraction and reflection
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RF LoS
Can be blocked by the fresnel zone ,unline VLoS
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Fresnel Zone
- area around the VLoS
- 3 dimentual .60 % of the radious of the VLoS
- Water obsorbs RF signals.
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Beamwidths
the width of the antenna beam ( horizontal and vertical )
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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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