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MSF
5000
Instruction Manual
Chapter
1
Description
Uniboard
isolation Buffer
The isolation
buffer stage ensures isolation between the
VCO
output and
the
IPA,
and prevents
pulling
of the
VCO
output frequency during transmitter key-up.
The Transmit
VCO RF
signal is passed through
the
isolation buffer prior
to
being
applied
to the first stage
of
the
IPA. The isolation buffer
consists of
input and
output matching circuits and an active device (Q326) that is biased for class
A
operation.
Modulation Compensation
Circuit
The modulation compensation circuit
enables
low
frequency modulation to be
transmitted without being "tracked out"
by
the loop.
When
the
VCO
is
modulated
by
data,
it
is
divided down
and compared to
the reference
signal. The
modulation appears
as an error
signal at
the phase detector. Unless compensated,
this error signal passes through the loop filter and modulates the steering line,
distorting
the intended data modulation.
The sensitivity of
the
modulation
compensation is set
via
R358.
Refer
to
Chapter
4
-
Alignment
to
adjust R358.
Receive Synthesizer Circuitry
The receive synthesizer is of
the same basic
design
as the
transmit synthesizer.
The major
difference is that the receive synthesizer generates the receive injection
signal. It
does not contain the
modulation compensation circuitry or isolation
buffer
as the
transmit synthesizer.
The functional
circuits of the receive synthesizer include the following:
0
Phase-Locked Loop
Circuitry
O
Super Filter
Refer
to
Figure
1-27
for
a
functional block diagram of
the receive synthesizer.
Receiver I-F Amplifier/Detector
68P81092E02
3/19/94
The
balanced output of the mixer is connected
to the
Intermediate Frequency
(I-F)
amplifier
detector circuit.
This I-F signal
is applied first
to
a
crystal filter
before
.
being applied
to
the
I-F
amplifier.
The signal is further amplified and filtered
before
being applied
to the
limiter/detector.
NOE
Refer
to
the
Receiver
Circuitry
section for
a
description of the receiver front end, prior to reaching
the
I-F
amplifier
/
detector.
1-55
MSF
5000
Instruction Manual
Chapter
1
Description
Uniboard
isolation Buffer
The isolation
buffer stage ensures isolation between the
VCO
output and
the
IPA,
and prevents
pulling
of the
VCO
output frequency during transmitter key-up.
The Transmit
VCO RF
signal is passed through
the
isolation buffer prior
to
being
applied
to the first stage
of
the
IPA. The isolation buffer
consists of
input and
output matching circuits and an active device (Q326) that is biased for class
A
operation.
Modulation Compensation
Circuit
The modulation compensation circuit
enables
low
frequency modulation to be
transmitted without being "tracked out"
by
the loop.
When
the
VCO
is
modulated
by
data,
it
is
divided down
and compared to
the reference
signal. The
modulation appears
as an error
signal at
the phase detector. Unless compensated,
this error signal passes through the loop filter and modulates the steering line,
distorting
the intended data modulation.
The sensitivity of
the
modulation
compensation is set
via
R358.
Refer
to
Chapter
4
-
Alignment
to
adjust R358.
Receive Synthesizer Circuitry
The receive synthesizer is of
the same basic
design
as the
transmit synthesizer.
The major
difference is that the receive synthesizer generates the receive injection
signal. It
does not contain the
modulation compensation circuitry or isolation
buffer
as the
transmit synthesizer.
The functional
circuits of the receive synthesizer include the following:
0
Phase-Locked Loop
Circuitry
O
Super Filter
Refer
to
Figure
1-27
for
a
functional block diagram of
the receive synthesizer.
Receiver I-F Amplifier/Detector
68P81092E02
3/19/94
The
balanced output of the mixer is connected
to the
Intermediate Frequency
(I-F)
amplifier
detector circuit.
This I-F signal
is applied first
to
a
crystal filter
before
.
being applied
to
the
I-F
amplifier.
The signal is further amplified and filtered
before
being applied
to the
limiter/detector.
NOE
Refer
to
the
Receiver
Circuitry
section for
a
description of the receiver front end, prior to reaching
the
I-F
amplifier
/
detector.
1-55
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