Lexicon RV-8 Service Manual page 125

Lexicon
voltage-summing node. The common side of each antenna terminal is tied directly to the rear panel
chassis via LUG1.
Tuner Module (U4)
The heart of the design is the Microtune UT1384 Tuner module. This device provides all RF
descrimination and provides as outputs AM program material in analog audio format, multiplexed FM
program material in the form of an analog signal, and Radio Data Stream (RDS) material in the form of an
analog signal. The RDS output provides both RDS data and multiplexed FM material on the same pin.
The module also provides a field strength signal in the form of a proportional DC voltage at pin 15.
Incoming signal strength and quality are further represented by the AF_SAMP and AF_HOLD signals
(pins 20 and 19, respectively). These signals are used to control an off-module sample and hold that will
store the average value of the analog signals output by the module. The processor chip U2 contains the
sample and hold function. A reference signal of 75.4kHz is available for external processing via the FREF
pin (pin 21). This signal is typically divided down to 38kHz and 19kHz to provide demultiplexing of the
RDS signal information and the left and right audio samples of the FM program material, respectively.
CPU command and control to the module is provided via an I
SDA (pin 11) and a serial shift clock SCL (pin 10). Station selection via the on-board PLL synthesizer, as
well as selection of AM or FM programming, is accomplished via this I
Two voltage supply rails are present on this module. VCC5 (pin 5) is a standard 5V supply input that
powers the digital logic inside the module, while all of the analog functionality, such as the PLL
synthesizer, signal strength, and signal quality control is powered by VCC8P5 (pin 6). This is an 8.5V DC
supply. The five volt rail is de-coupled by C10 and C11, while the 8.5V rail is de-coupled by C8 and C9.
The AM AF signal, FM MPX, and the FM/RDS signals are AC coupled to the CRISP processor (U2) via
C3, C5, and C2 respectively. R2 and C4 form a de-emphasis filter for the FM MPX signal, but as we are
decoding this from the combined FM/RDS stream, this option is left unused. R1 provides the FM/RDS
signal to both the RDS and FM inputs of U2.
Signal Processor (U2)
The signals provided by tuner module U4 are processed by U2, a Philips TEF6892H device. This is a
signal processor with on-board DSP that is intended for use in car audio systems. Although signal paths
for Cellphone, CD player, and Cassette Tape are provided, they are unused in this application. All radio
signal de-multiplexing and enhancements are made via this device. The AM signal is processed to
remove noise caused by external sources, such as AC line disturbances and path loss, and gain
controlled based upon the signal strength as provided via the LEVEL signal (pin 1). AM is introduced into
the device via pin 7, and the FM/RDS via pin 6. The AFSAMP and AFHOLD (pins 10 and 9, respectively)
are provided with the sample and hold control signals from the tuner block, and in conjunction with the
LEVEL pin, are used to provide an average voltage of the radio signal levels, which in turn determines
signal strength. The FREF signal from the tuner is introduced by pin 11, and is internally divided down to
provide the de-multiplexing pilot signals for FM and for the RDS. Volume and Equalization are controlled
2
within U2 via the I C bus pins SDA and SCL (pins 42 and 43, respectively). This is the same bus that
P
P
provides control of the tuner module. A gated equivalent of this bus is provided via SCLG and SDAG
(pins 3 and 4, respectively) and are provided a path to the tuner module by R4 and R7. This was to
accommodate using a single register set to control all functionality on the board, but as it was determined
to not be necessary, this option remains unused. R5 and R6 pass the I
The I C bus provides CPU control of the radio signal AGC and indication of stereo signal detection, as
2
B B
well as capabilities to provide overall signal level and equalization control at this level of implementation.
Left and Right audio signals are presented to the rest of the RV-8 system via LFOUT and RFOUT (pins
27 and 28, respectively). C12 and C13 provide an AC couple path to the output of the board, while R8
and R9 ensure equal path impedance for these signals. R16 further balances the common return path for
the output signals. C14 and C15 provide a high frequency roll-off for noise in conjunction with R8 and R9.
C20 provides storage of a reference voltage used by the internal D/A converters in the control path of U2.
2
C bus, comprised of a serial data stream
P P
2
C bus.
P
P
2
C bus along to the tuner block.
P
P
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