User's Manual

Glossary
46
SpotCell 100, Release 1.0
dBm A signal strength or power level. 0 dBm is
defined as 1 mW (milliWatt) of power into a 50
ohm load such as an ante nna. Small signals
are negative numbers. This is useful since
dB shows values in a logarithmic scale, not
linear.
RULE OF THUMB: Every time you double (or
halve) the power level; you add (or subtract) 3
dB. For example, 125 mW is 21 dBm and
250 mW is 24 dBm.
Directional Donor
Unit DDU
This is the SpotCell 100 system element that
is installed with a directional antenna aimed at
the nearest cellular base-station. This unit
may often be installed outdoors. The term
donor is widely used in the repeater industry
for the antenna that supports the air interface
to the network.
Effective Radi-
ated Power
(ERP)
Effective radiated power. It is equal to the sum
of the antenna gain (in dBi) plus the power (in
dBm) into that antenna. For example, a 12
dBi gain antenna fed directly with 15 dBm of
power has an Effective Radiated Power (ERP)
of:
12 dBi + 15dBm = 27 dBm or 500mW.
Isolation RF isolation is a measure of the path loss or
attenuation between two antennas. Path loss
typically must be 15dB or higher than the
required system gain for a repeater to function
properly.