Fig. 2-4. Front panel controls
FINE-A one turn control that operates in conjunction with
FINE RF CENTER FREQ-A 10 turn control to provide a
the IF control to provide a fine adjustment of the IF center
fine adjustment of the RF local oscillator frequency.
Especially useful in tuning the oscillator to a phase lock
condition with the reference frequency.
CAL-With the IF CENTER FREQ control centered, it cali-
brates the IF center frequency to 200 MHz.
MIXER PEAKING-A two position control that optimizes
the conversion of the first local oscillator for bands B and
VIDEO FILTER-With the switch in the up position, the
video bandwidth is restricted, to reduce high frequency
C. Does not affect band A. In the SEARCH position the
video components such as noise, and reduce zero beats
mixer current is swept through a range by the sweep volt-
when viewing signals near minimum resolution.
age. This insures an optimum mixer conversion or sensi-
tivity point within the dispersion range of the analyzer, so
VERTICAL DISPLAY-Selects logarithmic, linear or square-
all signals within a given dispersion pass through this opti-
law display. In the LOG position, signal display amplitude
mum sensitivity point as the signals are tuned across the
is a logarithmic function with a
screen. The manual (0 to 10) position of the control pro-
In the LIN position, signal display amplitude is a linear
vides an adjustment to optimize mixer conversion for any
range. In the SQ LAW position
function with a
fixed center frequency setting.
signal display amplitude is a square law function and the
display is a function of signal power, The SQ LAW posi-
LOCK CHECK-A push button switch that applies the
tion has a ≥13 d B d y n a m i c r a n g e .
phase lock output beat signal (between the local oscillator
and reference frequency) to the vertical display system.
POWER-Turns power off and on to the Type 491.
Provides a visual indication to the operator of phase lock
INDICATOR LIGHT-indicates when POWER is applied to
the Type 491.
INT REF FREQ-A switch and control. The control varies
RF CENTER FREQUENCY-Tunes RF center frequency from
the internal 1 MHz Reference Frequency over a range of
10 MHz to 40 GHz. With the IF CENTER FREQ control in
approximately 1 kHz. With the control in the OFF posi-
the 0 position, the RF CENTER FREQUENCY dial indicates
tion, the Internal Reference Frequency is turned off, and
the center frequency of the display.
an externally applied signal to the EXT REF FREQ IN
BAND SELECTOR-Switch selects RF Inputs and bands;
(1 MHz MARKERS OUT) connector becomes the reference
A (10-275 MHz), B (270-2000 MHz) and C (1.5-40 GHz).