Fluke 6060B Instruction Manual page 103

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C23 �;ouples the VCO signal to the Synthesizer assembly by a through-the-plate coaxial
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connector P 104. The other VCO signal is connected to the Output assembly A2A4 by a
plug-in capacitor, A2C l . This plug-in capacitor allows either VCO or the Output PCA to
be removed independently from the module A2 assembly without the use of a soldering
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iron.
Output PCA, A2A4
3-51.
The Output PCA accepts RF signals from the Synthesizer and the VCO circuits and
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command signals from the Controller. The output circuit provides a 0.01-MHz to
1050-MHz RF signal to the Attenuator .
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The Output assembly reduces harmonic distortion components in the RF signal,
controls RF signal amplitude, introduces AM, and generates the low (heterodyne)
frequency band 0.01 MHz to 245 MHz though mixing. It also generates a modulation
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signal to provide internal AM and FM, and provides a digital interconnect path between
the Controller and Synthesizer.
3-52. RF PATH
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The RF path begins with the two RF signals from the VCO and the Synthesizer
assemblies. The SPOT bandswitch circuit selects between the 5 1 2-MHz to 1050-MHz
signal at P I06 and the 245-MHz to 5 12-MHz signal at P107. The selected signal is
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applied to buffer amplifier Q 10 I and Q I 02.
The 245-to 5 1 2-MHz signal directly generates the 245-to 5 1 2-MHz mid-band output
signal. The 5 1 2-MHz to 1050-MHz signal generates the 5 1 2-MHz to 1050-MHz high­
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band output signal directly and the 0.01-MHz to 245-MHz low-band output signal by
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with an 800-MHz LO signal.
mixing
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The buffer amplifier Q 10 I and Q I 02 is a common-base, common-emitter cascade circuit
with 7-dB gain. The three cascaded filter circuits that follow the buffer amplifier consist of
combinations of discrete components and printed filters that suppress harmonics in the
Generator RF output signal.
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The first section of the circuit is a printed 1 100-MHz low-pass filter. The second section is
switched into the RF path via PIN diodes CR106 through CR I IO by asserting MIDL
when the Generator is operated in the mid-band (245 to 512 M Hz). PIN diodes CR1 1 4
through CR I 1 6 select capacitors C1 19, C i 2 1 , and Cl23 whenever HAOCTH is asserted
to change the section cutoff frequency from 5 1 2 to 350 MHz. The third sectio�;� provides
harmonic filtering for the two higher bands, 512 MHz t o 730 MHz, and 730 MHz to 1050
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MHz. PIN diodes CRi l l through CRI B select capacitors C 1 12 through C 1 1 4 to change
the cutoff frequency from 1050 MHz to 730 MHz whenever HAOCTH is not asserted.
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The amplitude modulator consists of PIN diodes CR 1 1 7 through CR 120 and associated
components and follows the switchable filters in the signal path. The modulator is a
voltage-controlled variable attenuator that provides AM and output level contr ol.
Modulator control voltage is determined by the leveling-loop circuitry. The leveling loop
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is described later in this section.
Q209, Q21 1 , Q213, and associated components follow the modulator in the signal path
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and form a three-stage, 2Q-dB gain, 245-MHz to 1050-MHz amplifier. This amplifier
drives a 3-dB power splitter that consists of resistors R253 through R255 and associated
printed transmission lines .
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One power splitter output drives the leveling-loop detector diode CR202. The other
output goes to the HET band switch that includes PIN diodes CR203 through CR210 and
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THEORY OF OPERATION
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