User's Manual

68P80801E35-B 5/1/2002 7
EBTS System Manual - Vol 2 Base Radio Exciter
800 Legacy MHz Exciter – TLN3337; 900 MHz Exciter – CLN1357; 1500 MHz Exciter – TLN3428
passed through the low-pass loop filter to the 970 MHz Voltage Controlled
Oscillator (VCO) circuit (1025 MHz VCO for 900 MHz BR).
970/1025 MHz Voltage Controlled Oscillator (VCO)
The 970 MHz VCO (1025 MHz for 900 MHz BR, 700 MHz for 1500 MHz BR)
generates the second injection frequency for the Exciter IC.
The VCO requires a very low-noise DC supply voltage of +10 VDC for proper
operation. The oscillator is driven by a Super Filter that contains an ultra
low-pass filter. The Super Filter obtains the required low-noise output voltage for
the oscillator.
The output of the oscillator is tapped and sent to the VCO Feedback Filter. This
feedback signal is supplied to the Synthesizer circuitry for the generation of
correction pulses.
The untapped output of the 970 (or 1025) MHz VCO is sent to the second LO
injection circuitry.
236/237/180.6 MHz Voltage Controlled Oscillator (VCO)
The 237 MHz VCO (180.6 MHz for 900 MHz BR, 236 MHz for 1500 MHz BR)
provides a LO signal to Tranlin IC for the first up-conversion and for the second
down-conversion of the feedback signal. The synthesizer and divide by 2
circuitry within the Tranlin IC set the first IF to 118.5 MHz (90.3 MHz for 900 MHz
BR).
Regulator Circuity
This circuit generates three regulated voltages of +5 VDC, +10 VDC, and +11.8
VDC. All voltages are obtained from the +14.2 VDC backplane voltage. These
voltages are used to power various ICs and RF devices of the Exciter.
Linear RF Amplifier Stages
This circuitry is used to amplify the RF signal from the Exciter IC to an
appropriate level for input to the PA.
Automatic Gain Control (AGC) (1500 MHz only)
The Automatic Gain Control (AGC) circuit controls the output gain of the
transmitter (Exciter and Power Amplifier modules) so that constant forward gain
of the RF amplifier stages is maintained. This is accomplished through the
comparison of feedback signals from the Power Amplifier and the first amplifier
stage of the Exciter.
The output of the differential amplifiers is used to adjust the Attenuator and
Image Filter.