Bird Technologies 61-89A-50 Series-Installation Instructions - Manual (Page 11)

Manual 7-9362-2 Page 5 TX RX Systems Inc. 10/19/05
Use of these terminals is optional. SB II also has a
number of status LEDs built-in to individual mod-
ules to indicate a fault condition.
RF Connections
N(F) bulkhead connectors are provided on the bot-
tom of the cabinet for connection to the signal dis-
tribution system. Be sure that the correct branch of
the distribution system is connected to its corre-
sponding Uplink/Downlink connector or the system
will not work properly. Using high-quality connec-
tors with gold center pins is advised. Flexible
jumper cables made of high-quality coax are also
acceptable for connecting to rigid cable sections.
CAUTION: The maximum RF input
power level for the SBII is -15 dBm.
Stronger input signals will cause the
unit to exceed it’s IM specifications.
Input signals stronger than 0 dBm
will physically damage the unit.
PRE-RF CONNECTION TESTS
Antenna isolation between the uplink and downlink
branches should be measured before connecting
the signal booster to the antenna system. This step
is necessary to insure that no conditions exist that
could possibly damage the signal booster and
should not be skipped for even the most thoroughly
designed system.
Note: The 80 dB gain models are fac-
tory preset to 50 dB gain and should
only be reset to a higher value after
determining the safe maximum gain
based on antenna isolation
Test Equipment
The following equipment is required in order to per-
form the pre-installation measurements.
1) Signal generator for the frequencies of interest
capable of a 0 dBm output level. Modulation is
not necessary.
2) Spectrum analyzer that covers the frequencies
of interest and is capable of observing signal
levels down to -100 dBm or better.
3) Double shielded coaxial test cables made from
RG142, RG55 or RG223 coaxial cable.
Antenna Isolation
Just like the feedback squeal that can occur when
the microphone and speaker get too close to each
other in a public address system, a signal booster
can start to self oscillate. This can occur when the
isolation between the input antenna or signal
source and the output distribution system does not
exceed the signal boosters gain by at least 15 dB.
Oscillation will reduce the effectiveness of the sys-
tem and may possibly damage the power amplifier
stages.
In general, if one or both antenna ports are con-
nected to sections of radiating coaxial cable (lossy
cable) the isolation will be more than adequate
because of the high coupling loss values that are
encountered with this type of cable. When a net-
work of antennas are used for the input and output,
this problem is much more likely. Isolation values
are relatively easy to measure with a spectrum
analyzer and signal generator.
Procedure for Measuring Antenna Isolation
1) Set the signal generator for a 0 dBm output
level at the center frequency of one of the signal
boosters passbands (815 or 860 MHz)
2) Set the spectrum analyzer for the same center
frequency and a sweep width equal to or just
slightly greater than the passband (18 MHz)
chosen in step one.
3) Connect the test leads of the signal generator
and the spectrum analyzer together using a
female barrel connector, see
Figure 4. Observe
the signal on the analyzer and adjust the input
attenuator of the spectrum analyzer for a signal
level that just reaches the 0 dBm level at the top
of the graticule.
4) Referring to figure 4, connect the generator test
lead to one side of the signal distribution system
(external antenna) and the spectrum analyzer
lead to the other (internal distribution system)
and observe the signal level. The difference
between this observed level and 0 dBm is the
isolation between the sections. If the signal is
too weak to observe, the spectrum analyzer's
bandwidth may have to be narrowed and its
input attenuation reduced. Record the isolation
value.
The isolation value measured should
exceed the signal booster’s gain figure by at
least 15 dB.
NOTE