16 |
P a ge
DIAGNOSTICS
GUIDE
The
BDA
provides
long
term,
care
‐
free
operation
and
requires
no
periodic
maintenance.
There
are
no
user
‐
serviceable
components
inside
the
BDA.
This
section
covers
possible
problems
that
may
be
related
to
the
installation
or
operating
environment.
Gain
Reduction
Possible
causes:
Bad
RF
cables
and
RF
connections
to
antennas,
damaged
antennas.
Occasional
Drop
‐
out
of
some
Channels
Possible
causes:
One
channel
with
very
strong
power
dominates
the
RF
output
of
the
amplifier.
ANTENNA
SEPERATION
BDA
oscillation
is
caused
by
low
isolation
(antenna
separation)
between
donor
antenna
and
service
antennas.
The
recommended
isolation
between
those
antennas
is
15db
above
the
system
gain.
The
amount
of
isolation
that
can
be
achieved
between
antennas
depends
on
several
factors,
such
as
the
physical
vertical
and
horizontal
separation
(distance
between
the
antennas),
polarization,
radiation
pattern
of
the
antennas,
the
medium
between
the
antennas,
antenna
gain
etc.
Antenna
isolation
can
most
accurately
be
determined
through
on
‐
site
measurements
An
antenna
isolation
measurement
configuration
is
illustrated
in
Figure
6,
where
two
spatially
separated
antennas
(service
antenna
#1
and
donor
antenna
#2)
are
connected
to
a
signal
generator
and
signal
analyzer.
A
signal
at
center
frequency
is
generated
by
the
signal
generator
sent
to
the
input
of
antenna
1;
the
output
of
the
signal
at
antenna
2
is
measured
and
recorded
by
the
signal
analyzer.
With
calibrated
connection
cables,
by
taking
into
account
the
cable
loss,
the
difference
of
signal
power
level
at
the
output
of
antenna
2
and
that
at
the
antenna
1
input
is
taken
as
antenna
isolation.
(See
Appendix
2
for
analytical
calculation
)
Figure 6
