User's Guide

Units of Measure
201
Units of Measure
Attenuation and
Gain
Attenuation is a decrease in amplitude due to signal absorption or dispersion. Gain is an
increase in amplitude due to different forms of signal enhancement, such as the use of an
antenna to focus the signal. Amplitude and gain are measured in decibels (dB).
Antenna gain is measured relative to the strength of the signal you would receive at any
given distance using an antenna with no gain (such as a dipole or theoretic Isotropic
antenna).
The antennas at both ends of the link can enhance signal gain. The total gain for a connec-
tion between two antennas is the product of the gains for both antennas.
Signal
Measurement
To measure the size and strength of a signal meaningfully, we must consider the following:
• A signal widens with distance. To calculate the height and width of a signal, we must
know the distance from its source.
• A signal has no distinct outer edge. It is strongest in a narrow focused area (center
lobe), and it fades out gradually as distance increases from the center lobe.
How we measure the cone –
How we measure the cone –How we measure the cone –
How we measure the cone – To indicate the shape of the cone, we measure its expansion
in degrees.
How we measure signal strength –
How we measure signal strength –How we measure signal strength –
How we measure signal strength – We measure signal strength relative to the center point
where the signal is strongest, but we generally do not say how strong the signal is at that
point.
How we measure signal width –
How we measure signal width –How we measure signal width –
How we measure signal width – To avoid measuring from a nebulous edge, we measure
across the center point at different bands of signal strength. The number of decibels (dB
units) indicates threshold points relative to the center point.
For example, the beam width of the Solectek dish antenna we define as 17.5× maximum
at 3 dB elevation. Three dB is a threshold within the cone where the signal’s strength is
50% lower than its strength at the center. The drawing below shows the beam width at
different dB increments relative to the center of a signal formed by a dish antenna.
Decibel. The decibel (dB) is used as a measure of both attenuation and gain.
3 dB = 50% signal strength
1 dB = 80% signal strength
center lobe = 100% signal strength
1 dB = 80% signal strength
3 dB = 50% signal strength