TIM-5H
-
Hardware
Integration
Manual
Design-In
GPS.G5-MS5-07015-A-1
u-blox
proprietary
Page 23
your position is our focus
For
u-blox
5
receivers,
the
total
preamplifier
gain
(minus
cable
and
interconnect
losses)
must
not
exceed
50
dB.
Total
noise
figure
should
be
below
3
dB.
The
u-blox
5
Technology
supports
either
a
short
circuit
protection
of
the
active
antenna
or
an
active
antenna
supervisor
circuit
(open
and
short
circuit
detection).
For
further
information
refer
to
Section 2.9.2).
2.9.1 Passive Antenna
A
design
using
a
passive
antenna
requires
more
attention
regarding
the
layout
of
the
RF
section.
Typically
a
passive
antenna
is
located
near
electronic
components;
therefore
care
should
be
taken
to
reduce
electrical
‘noise’
that
may
interfere
with
the
antenna
performance.
Passive
antennas
do
not
require
a
DC
bias
voltage
and
can
be
directly
connected
to
the
RF
input
pin
RF_IN
.
Sometimes,
they
may
also
need
a
passive
matching
network
to
match
the
impedance
to
50
Ohms.
Some
passive
antenna
designs
present
a
DC
short
to
the
RF
input,
when
connected.
If
a
system
is
designed
with
antenna
bias
supply
AND
there
is
a
chance
of
a
passive
antenna
being
connected
to
the
design,
consider
a
short
circuit
protection.
All
u-blox
5
receivers
have
a
built-in
LNA
required
for
passive
antennas.
2.9.2 Active Antenna
Active
antennas
have
an
integrated
low-noise
amplifier.
They
can
be
directly
connected
to
RF_IN
.
If
an
active
antenna
is
connected
to
RF_IN
,
the
integrated
low-noise
amplifier
of
the
antenna
needs
to
be
supplied
with
the
correct
voltage
through
pin
V_ANT
or
an
external
inductor.
Usually,
the
supply
voltage
is
fed
to
the
antenna
through
the
coaxial
RF
cable.
Active
antennas
require
a
power
supply
that
will
contribute
to
the
total
GPS
system
power
consumption
budget
with
additional
5
to
20
mA
typically.
Inside
the
antenna,
the
DC
component
on
the
inner
conductor
will
be
separated
from
the
RF
signal
and
routed
to
the
supply
pin
of
the
LNA
(see
Antenna
Low Noise Amplifier LNA
Coaxial Antenna Cable
Active Antenna
RF Front
End
GND
RF_IN
GND
V_ANT
19
17
V_ANT
Figure 12: Active antenna biasing
Generally
an
active
antenna
is
easier
to
integrate
into
a
system
design,
as
it
is
less
sensitive
to
jamming
compared
to
a
passive
antenna.
But
an
active
antenna
must
also
be
placed
far
from
any
noise
sources
to
have
good
performance.
Antennas should only be connected to the receiver when the receiver is not powered. Do not
connect or disconnect the Antenna when the u-blox 5 receiver is running as the receiver
calibrates the noise floor on power-up. Connecting the antenna after power-up can result in
prolonged acquisition time.
Never feed supply voltage into RF_IN. Always feed via V_ANT or an external inductor .
To
test
GPS/GALILEO
signal
reacquisition,
it
is
recommended
to
physically
block
the
signal
to
the
antenna,
rather
than
disconnecting
and
reconnecting
the
receiver.
