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g. Receiving
The signal received
at the antenna is routed
through the filter/detector/switch module
(U203)
and
applied
to the
receiver
rf
front
end module
for filtering,
amplification, and mixing down to the
first
i-f.
(1) RF and
{st I-F
(a) Mid-Band
(U1, U4)
In
the mid-band receiver string,
rf
enters U1, the
rf
filter/amplifier module.
This
module
consists
of
a
dis-
crete-component, 3-pole bandpass
filter,
designed
to
cover
either the low
(68-84 MHz)
or the high
(74-88
MHz) bandsplit,
and a
common-base, transformer
feedback
amplifier.
The
entire module provides about
9dB
of
gain.
The
rf
signal leaves
U1
on pin
9 and enters the
receiver
front-end module, U4, on pin 2. Within U4 the
signal
first
enters another 3-pole bandpass
filter of the
same
type
as
in
U1
(about
2dB
insertion
loss).
Next,
the signal moves
into
a double-balanced
mixer,
where
it
is mixed with the local
oscillator
(LO) signal
from
U300
(pin 15).
The LO signal
enters the mixer (U4,
pin
3) at
a
level
of
+4.5
to
+5dBm, and one
i-f
(53.55MHz)
above
the channel
(rf)
frequency.
The
resultant first
i-f
signal (53.55MHz)
from the
mixer then
passes
through U4's
i-f
amplifier and
crys-
tal filter before exiting the module (pin
4). There
is
a
loss
of about 6 to
7dB
through the mixer, the
i-f
ampli-
fier provides about
13B
of
gain, and the crystal
filter
has about 3.5dB
insertion loss.
The
crystal
filter
sup-
plies about 35dB
of
attenuation at the adjacent
chan-
nel and
80dB
of
attenuation at the second image.
The
bandwidth of the
i-f
signal leaving U4
is
typically
10 to
19kHz, centered
on
53.55MHz,
with
a typical gain
of 0
to
2dB.
The
first i-f
signal
now
moves
through match-
ing
components
C49
and L2 before entering the
i-f
IC,
U100.
(b)
VHF
(U1,
Qt,
T1, U2, U4)
In
the vhf receiver string,
rf
enters U1, the 2-pole
filter module; this module
has about 2dB
of
insertion
loss. For
low split radios
(136-150.8 MHz), a
fixed-
tuned filter
is
used;
for high split
models (146-178
MHz), a tunable
filter
design
is
used.
This
filter
has a
bandwidth of about 16MHz, and
can be
tuned to
cover
the entire
146-178 MHz band, depending
upon the
applied voltage
from
the digital/analog converter IC,
U200.
Pin
No.
Function
Signal
The
rf
signal leaves
U1
(pin 11) and
enters the
rf
amplifier, Q3.
This
is a
common-base, transformer
feedback
amplifier, with the output
signal leaving
through the center tap of transformer T1 (pin 1).
The
amplifier provides about 10dB of gain over the entire
vhf frequency band.
The
rf
signal
next
passes
through matching
com-
ponents
C54
and
L52,
and
into
the 5-pole
filter,
U2
(pin 1).
A 32MHz-bandwidth, stripline
filter module
containing some discrete components, U2 has a typi-
cal
insertion
loss
of
about 3.5dB.
18
No connection
Don't
care
19
Ground
Ground
20
2.1
MHz
in
2.1
MHz signal
21
No connection
Don't
care
22
Digital
Vdd
5V
23, 24
No connection
Don't
care
25
Limiter out
Toggles
between
OV and
5V
in
receive mode
26
HS
bypass
Don't
care
27
LS
bypass
Don't
care
28
No connection
Don't
care
29
VAG bypass
Don't
care
30
No connection
Don't
care
31
RX
audio
in
The analog
demodulated
signal
32-34
No connection
Don't
care
35
Ground
Ground
36
No connection
Don't
care
After leaving U2
(pin
2), the
rf
signal enters
the
front
end module, U4 (pin 2), which is mounted directly
above
U2. Within U4 the
signal
first
moves
into
the
double-balanced
mixer,
where
it
is mixed with the local
oscillator
(LO)
signal
from
U300
(pin 15).
The LO sig-
nal
enters the mixer
(pin 3) at a
level
of
+4.5
to
+5dBm, and one
i-f
(53.55MHz) above
the channel
(rf)
frequency.
The
resultant first
i-f
signal (53.55MHz)
from
the
mixer then
passes
through
U4's
i-f
amplifier and
crys-
tal filter before exiting the module (pin
4). There
is
a
loss
of
about 6 to 7dB through the mixer, the
i-f
ampli-
fier
provides about 10B
of
gain, and
the
crystal
filter
has about 3.5dB
insertion
loss.
The
crystal
filter
sup-
plies some 40dB
of
attenuation at the adjacent chan-
nel
and 80dB of attenuation at the second image.
The
bandwidth of the
i-f
signal leaving U4 is typically
12 to
16kHz, centered
on
53.55MHz,
with
a typical gain
of 0
to
3dB. The
first i-f
signal now moves through match-
ing
components
C49
and L2 before entering the
i-f
IC,
U100.
(c)
UHF
(U2)
After leaving
FDS
module U203
(pin
9), the
rf
sig-
nal
enters the
front end module, U2 (pin
2). Within U2
the
signal
first
passes
through
a 30MHz-wide
stripline
filter,
an
rf
amplifier, and another
30MHz-wide siripline
filter.
The
rf
amplifier supplies 10dB of gain over one of
two bandsplits:
403
-
470MHz
or
450
-
520MHz. Next,
the
rf
signal enters a double-balanced
mixer,
where
it
is mixed with the local
oscillator
(LO) signal
from
syn-
thesizer U300
(pin 15).
The LO
signal enters the
mixer
(pin 4) at a
level
of
+4.5
to
+5dBm,
and one i-f
(73.35MHz) below
the
channel
(rf)
frequency.
The
resultant first
i-f
signal (73.35MHz)
from
the
mixer then
passes
through U2's
i-f
amplifier and
crys-
tal filter before exiting the module (pin
4). There
is
a
loss
of
about 6
to
7dB through the
mixer, the i-f ampli-
fier provides about
10B
of
gain,
and the
crystal
filter
has about 3.5dB insertion loss.
The
crystal
filter
sup-
plies some 40dB
of
attenuation at the adjacent
chan-
nel
and 80dB of attenuation at the second image.
The
11
g. Receiving
The signal received
at the antenna is routed
through the filter/detector/switch module
(U203)
and
applied
to the
receiver
rf
front
end module
for filtering,
amplification, and mixing down to the
first
i-f.
(1) RF and
{st I-F
(a) Mid-Band
(U1, U4)
In
the mid-band receiver string,
rf
enters U1, the
rf
filter/amplifier module.
This
module
consists
of
a
dis-
crete-component, 3-pole bandpass
filter,
designed
to
cover
either the low
(68-84 MHz)
or the high
(74-88
MHz) bandsplit,
and a
common-base, transformer
feedback
amplifier.
The
entire module provides about
9dB
of
gain.
The
rf
signal leaves
U1
on pin
9 and enters the
receiver
front-end module, U4, on pin 2. Within U4 the
signal
first
enters another 3-pole bandpass
filter of the
same
type
as
in
U1
(about
2dB
insertion
loss).
Next,
the signal moves
into
a double-balanced
mixer,
where
it
is mixed with the local
oscillator
(LO) signal
from
U300
(pin 15).
The LO signal
enters the mixer (U4,
pin
3) at
a
level
of
+4.5
to
+5dBm, and one
i-f
(53.55MHz)
above
the channel
(rf)
frequency.
The
resultant first
i-f
signal (53.55MHz)
from the
mixer then
passes
through U4's
i-f
amplifier and
crys-
tal filter before exiting the module (pin
4). There
is
a
loss
of about 6 to
7dB
through the mixer, the
i-f
ampli-
fier provides about
13B
of
gain, and the crystal
filter
has about 3.5dB
insertion loss.
The
crystal
filter
sup-
plies about 35dB
of
attenuation at the adjacent
chan-
nel and
80dB
of
attenuation at the second image.
The
bandwidth of the
i-f
signal leaving U4
is
typically
10 to
19kHz, centered
on
53.55MHz,
with
a typical gain
of 0
to
2dB.
The
first i-f
signal
now
moves
through match-
ing
components
C49
and L2 before entering the
i-f
IC,
U100.
(b)
VHF
(U1,
Qt,
T1, U2, U4)
In
the vhf receiver string,
rf
enters U1, the 2-pole
filter module; this module
has about 2dB
of
insertion
loss. For
low split radios
(136-150.8 MHz), a
fixed-
tuned filter
is
used;
for high split
models (146-178
MHz), a tunable
filter
design
is
used.
This
filter
has a
bandwidth of about 16MHz, and
can be
tuned to
cover
the entire
146-178 MHz band, depending
upon the
applied voltage
from
the digital/analog converter IC,
U200.
Pin
No.
Function
Signal
The
rf
signal leaves
U1
(pin 11) and
enters the
rf
amplifier, Q3.
This
is a
common-base, transformer
feedback
amplifier, with the output
signal leaving
through the center tap of transformer T1 (pin 1).
The
amplifier provides about 10dB of gain over the entire
vhf frequency band.
The
rf
signal
next
passes
through matching
com-
ponents
C54
and
L52,
and
into
the 5-pole
filter,
U2
(pin 1).
A 32MHz-bandwidth, stripline
filter module
containing some discrete components, U2 has a typi-
cal
insertion
loss
of
about 3.5dB.
18
No connection
Don't
care
19
Ground
Ground
20
2.1
MHz
in
2.1
MHz signal
21
No connection
Don't
care
22
Digital
Vdd
5V
23, 24
No connection
Don't
care
25
Limiter out
Toggles
between
OV and
5V
in
receive mode
26
HS
bypass
Don't
care
27
LS
bypass
Don't
care
28
No connection
Don't
care
29
VAG bypass
Don't
care
30
No connection
Don't
care
31
RX
audio
in
The analog
demodulated
signal
32-34
No connection
Don't
care
35
Ground
Ground
36
No connection
Don't
care
After leaving U2
(pin
2), the
rf
signal enters
the
front
end module, U4 (pin 2), which is mounted directly
above
U2. Within U4 the
signal
first
moves
into
the
double-balanced
mixer,
where
it
is mixed with the local
oscillator
(LO)
signal
from
U300
(pin 15).
The LO sig-
nal
enters the mixer
(pin 3) at a
level
of
+4.5
to
+5dBm, and one
i-f
(53.55MHz) above
the channel
(rf)
frequency.
The
resultant first
i-f
signal (53.55MHz)
from
the
mixer then
passes
through
U4's
i-f
amplifier and
crys-
tal filter before exiting the module (pin
4). There
is
a
loss
of
about 6 to 7dB through the mixer, the
i-f
ampli-
fier
provides about 10B
of
gain, and
the
crystal
filter
has about 3.5dB
insertion
loss.
The
crystal
filter
sup-
plies some 40dB
of
attenuation at the adjacent chan-
nel
and 80dB of attenuation at the second image.
The
bandwidth of the
i-f
signal leaving U4 is typically
12 to
16kHz, centered
on
53.55MHz,
with
a typical gain
of 0
to
3dB. The
first i-f
signal now moves through match-
ing
components
C49
and L2 before entering the
i-f
IC,
U100.
(c)
UHF
(U2)
After leaving
FDS
module U203
(pin
9), the
rf
sig-
nal
enters the
front end module, U2 (pin
2). Within U2
the
signal
first
passes
through
a 30MHz-wide
stripline
filter,
an
rf
amplifier, and another
30MHz-wide siripline
filter.
The
rf
amplifier supplies 10dB of gain over one of
two bandsplits:
403
-
470MHz
or
450
-
520MHz. Next,
the
rf
signal enters a double-balanced
mixer,
where
it
is mixed with the local
oscillator
(LO) signal
from
syn-
thesizer U300
(pin 15).
The LO
signal enters the
mixer
(pin 4) at a
level
of
+4.5
to
+5dBm,
and one i-f
(73.35MHz) below
the
channel
(rf)
frequency.
The
resultant first
i-f
signal (73.35MHz)
from
the
mixer then
passes
through U2's
i-f
amplifier and
crys-
tal filter before exiting the module (pin
4). There
is
a
loss
of
about 6
to
7dB through the
mixer, the i-f ampli-
fier provides about
10B
of
gain,
and the
crystal
filter
has about 3.5dB insertion loss.
The
crystal
filter
sup-
plies some 40dB
of
attenuation at the adjacent
chan-
nel
and 80dB of attenuation at the second image.
The
11
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