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9-21.
SINAD Detection.
The SINAD of a signal on the DVM FROM RNG SW line is determined by taking the
ratio of the input to the output signal power on the 1 kHz Notch Filter. Signal power is determined by Rectifier
and Filter circuits whose outputs are DC levels proportional to the input signal levels. The DC levels, SINAD IN
and SINAD OUT are digitized and input to the processor where the SINAD is calculated.
9-22.
Module Control.
Processor control of the Scope/ DVM Control module is via the AF ADD BUS 0-3, the
AF OAT A BUS 0-3. and the AF BUS EN 1 signal lines. The four address bits are decoded by the Address
Decode to determine which Control Latch the fours bits of data will be latched. The latching process is
synchronized by the enable line. Control latches in addition to those necessary for controlling the module
provide control for the Scope Amplifier module and part of the RF Input module.
9-4
SECTION 9
SCOPE/DVM CONTROL MODULE (A3)
9-1.
General.
A primary function of the Scope/DVM Control Module is to route the required measurement
and viewing signals to the DVM and scope circuitry. A large portion of the displayed data is determined by the
DVM measurements on internal signal points. Thus for a rapid update of several data displays it is necessary to
time division multiplex several measurement points to the DVM. The DVM control circuitry and the system
processor provide this function.
9-2.
The scope control circuitry allows the system to display data information. internal modulation or
demodulated signals, and external scope inputs as selected by the user. Provisions are also made for external
horizontal inputs and a horizontal sweep that is coherent with the sweep generator lor spectrum analyzer and
filter alignment displays.
9-3.
The control module also contains circuitry for single sideband demodulation and a IF phase locked loop
for filtering and waveshaping the IF signal lor frequency counting. A block diagram of the Scope/ DVM Control
module is shown in figure 9-1 with a schematic shown in figure 9-2.
9-4.
Scope Vertical Control. The input to the scope vertical amplifier is switched between four different
sources: the range switch (VERT FROM RNG SW), the vertical character sweep, the spectrum analyzer
(SPECT ANA VERT), or the 455kHz IF. Range switch inputs are from either the scope vertical input jack on the
front panel or the internal modulation signals as selected by the modulation display control on this module.
The vertical character sweep is a sawtooth waveform generated by the Vertical Character Sweep Generator
and synced by the VERT CHAR SYNC signal from the character generator. The detected and amplified output
of the receiver logarithimic IF is the vertical input for the spectrum analyzer. The remaining signal source is the
second IF signal from the receiver for IF envelope observation.
9-5.
For the spectrum analyzer and the scope sweep displays the Dual Display Control and Character Sweep
Counter circuitry allow a single row of characters at the top of the CRT. This function is implemented with the
Vertical Sweep Control by alternating the spectrum analyzer or the range switch signal with the vertical
character sweep signal.
9-6.
The dual display sequence of events starts with the Synthesizer Sweep Generator which is common to
both display modes. When the synthesizer sweep is near its peak (scope horizontal sweep is at the edge of the
screen) the Dual Display Control activates the CHAR GEN RST line and switches the scope vertical and
horizontal inputs to their character generator sweeps. When the first character line has been traced, a
transition on the LINE 1 input from the character generator resets the character generator sweeps and the
character generator, increments the Character Sweep Counter, and thus causes line 1 to be traced again. This
process repeats until four traces. as counted by the Character Sweep Counter, have been completed. At that
point the counter resets the scope inputs back to the spectrum analyzer or range switch input During the
character display time the synthesizer sweep generator is reset and held until a transition on the SYNTH SWP
SYNC line restarts the sweep. The timing of the process allows for the four character traces to be completed
before the sweep sync occurs.
9-7.
SSB Detection.
Single Sideband (SSB) modulation is recovered by multiplying the 455KHz IF signal
with a 455KHz beat frequency oscillat,or (BFO) signal. The BFO is controlled directly from the front panel and
is adjustable over a 6KHz frequency range. SSB AUDIO from the multiplier is routed to the receiver for post
9-1
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