UHF Analog Driver/Transmitter/
Chapter 4, Circuit Descriptions
Translator
LX Series, Rev. 3
4-12
all of the breakpoints past the signal
peaks so that they will have no affect.
The pre-distorted IF signal in the In
Phase path, connects to an op amp U18
whose output level is controlled by R238.
R238 provides a means of balancing the
level of the amplitude pre-distorted IF
signal that then connects to the combiner
Z2.
The pre-distorted IF signal in the
Quadrature path connects to op amp U20
and then step up transformer T9, next op
amp U21 and step up transformer T10
and finally op amp U22 whose output
level is controlled by R258. R258
provides a means of balancing the level
of the Phase pre-distorted IF signal that
then connects to the combiner Z2.
The Amplitude and Phase pre-distorted IF
signals are combined by Z2 and
connected to J37 that is jumpered to J36
on the board. J37 can be used for
testing or monitoring purposes of the IF
signal after Amplitude and Phase pre-
distortion. The pre-distorted IF signal
connects through a resistor buffer
network that prevents loading of the
combiner before it is wired to the
frequency response circuitry.
4.3.1.8 Main IF Signal Path (Part 3 of 3)
The IF signal, at the input to the
frequency-response corrector circuit, is
split using L24, L25 and R89. One path
is through L24, which is the main IF path
through the board. The main IF is fed
through a resistor network that controls
the level of the IF by adjusting the
resistance of R99, the output level
adjust. The IF signal is then applied to a
three-stage, frequency-response
corrector circuit that is adjusted as
needed.
The frequency-response corrector circuit
operates as follows. Variable resistors
R103, R106 and R274 are used to adjust
the depth and gain of the notches and
variable caps C71, C72 and C171 are
used to adjust the frequency position of
the notches. These are adjusted as
needed to compensate for frequency
response problems.
The frequency-response corrected IF is
connected to J38 that is jumpered to J39
on the board. J38 can be used for testing
or monitoring purposes of the IF signal
after frequency response pre-correction.
The IF is next amplified by U13 and U14.
After amplification, the IF is split with one
path connected to J42C pin 1C the IF
output to the LO/Upconverter Module. The
other path is fed through a divider network
to J35 a SMA IF Sample Jack, located on
the front panel, which provides a sample of
the corrected IF for test purposes.
4.3.1.9 ALC Circuit
The other path of the corrected IF signal at
the input to the frequency response
corrector circuit is used in the ALC circuit.
The IF flows through L25, of the L24 L25
splitter, and connects to the op-amp U12.
The IF signal is applied through a resistor
divider network to transformer T5. T5
doubles the voltage swing by means of a
1:4 impedance transformation before it is
connected to the ALC detector circuit,
consisting of C70, CR23 and R91. The
detected ALC level output is amplified by
U10B and wired to U10A, pin 2, where it is
summed with the power control setting,
which is the output power setting that is
maintained by the ALC. The output of
U10A connects through SW1, if it is in the
auto gain position, to the pin-diode
attenuator circuit, CR1, CR2 & CR3. The
high forward biases them more or less,
that increases or decreases the IF level,
therefore the output level, opposite the
input level. When the input signal level
increases, the forward bias on the pin
attenuator decreases, therefore the output
power will decrease, which keeps the
output power the same as set by the
customer.
An external power raise/lower switch can
be used by connecting it to TB30, at TB30-
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Страница 99: ...APPENDIX A LX SERIES ANALOG SYSTEM SPECIFICATIONS...
Страница 102: ...APPENDIX B DRAWINGS AND PARTS LISTS...
Страница 105: ...APPENDIX C TRANSMITTER LOG SHEET...
