Chapter 9 377
Assembly Descriptions and Block Diagrams
IF Section
A7 Analog Interface
The A7 analog interface assembly converts the digital commands from
the A16 assembly to analog control signals for the following assemblies
shown on Figure 9-1:
• DAC control of the A11/A13 bandwidth filter assemblies. Refer to
“Replacing Major Assemblies” in Chapter 7 for more information
about bandwidth switching.
❏ LC to crystal mode switching. BW5 controls switching between
crystal and LC bandwidth filter modes.
❏ Bandwidth control. The A7 bandwidth control DACs supply two
control lines to drive the PIN diodes on the A11 and A13
assemblies. Companding DACs are used because their nonlinear
output compensates for the nonlinear resistance-versus-current
of the PIN diodes they control.
• BW6 control line. Controls the crystal bandwidths from
30 kHz to 1 kHz. More DAC current produces a narrower
bandwidth in crystal mode.
• BW7 control line. Controls the LC bandwidths from 5 MHz to
100 kHz. In LC mode, more DAC current produces a wider
bandwidth.
Bandwidth error is corrected by the
CAL AMPTD
self-calibration routine. Refer to Chapter 13 for a description
of
CAL AMPTD.
• A12 amplitude control assembly. When the reference level is
changed, the A7 assembly switches the calibration attenuators and
the step gains on the A12 assembly to change the displayed signal
position. Refer to “Replacing Major Assemblies” in Chapter 7 for
more information about switching for the calibration attenuator, the
step gains, and the log/linear switch.
❏ Calibration attenuators. A TTL high on selected A7 control lines
activates a combination of attenuator steps. The 1, 2, 4, and 8 dB
step attenuators are combined to provide attenuation in 1 dB
increments. Currently, the 16 dB attenuator is not used.
❏ 10 dB step gains. Temperature-compensated control voltages
activate a combination of the three A12 step-gain stages. Step
gains are produced in 10 dB increments over a 50 dB range. Step
gain errors are corrected by the
CAL AMPTD self-calibration
routine. Refer to Chapter 13 for a description of
CAL AMPTD.
To Next Page
Loading...
Need help?
General
