Bird Technologies Group 26076 Manual De Usuario

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.

The booster is factory preset to 50 dB
gain and should only be reset to a
higher value after determining the
safe maximum gain based on antenna
isolation.

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.

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.

1) Set the signal generator for a 0 dBm output

level at the center frequency of one of the signal
boosters passbands.

2) Set the spectrum analyzer for the same center

frequency and a sweep width equal to or just
slightly greater than the passband 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 6. 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 6, 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 for future reference. The isolation value
measured should exceed the signal boost-
ers gain figure by at least 15 dB.

5) Repeat step 4 again with the signal generator

set at the passband edges in order to see if the
isolation is remaining relatively constant over
the complete width of the passband.

6) Repeat the isolation measurements if neces-

sary at other system passbands to determine
the overall minimum isolation value for the sys-
tem. Physical modification of the antenna sys-
tem maybe required in order to reach an
acceptable minimum value.

To comply with FCC RF exposure compliance
requirements, a separation distance of at least
32.5 cm (for UHF), 23 cm (for 700 MHz PS), 27 cm
(for 800 MHz PS), or 22 cm (for 800 MHz CRMS)
must be maintained between the Donor antenna of
this equipment and all persons. To comply with
FCC RF exposure compliance requirements, a
separation distance of at least 32.5 cm (for UHF),

NOTE