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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 for spectrum analyzer and
filter alignment displays.
9-3.
The control module also contains circuitry forsinglesideband demodulation and a IF phase locked loop
for filtering and waveshaping the IF signal for 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 eitherthescopevertical 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 455 KHz 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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