TM 11-6625-1559-12
Note. If the specified maximum sweep width is not
Note. Response should be within 0.5 decibel (db)
obtained, adjust the WOBB DRIVE LIMIT potentiometer
from 0.5 to 800 MHz and within 1.5 db from 800 to
clockwise until it is.
1,000 MHz. To check this, insert a high-quality, 1-db pad
between the generator sweep output and the D-50 detector
and note how far the trace falls. This action establishes
3-5. Interpretation of
Markers
a 1-db reference against which the response can be
measured. Remove the pad after making the response
check.
equipment testing, the frequency marker system
(birdy markers) must be understood and the in-
q. Using the 1-, 10-, and 100-MHz markers,
terpretation of the various markers observed on
check the range of the SWEEP WIDTH control.
the oscilloscope screen.
It should be from 500 kHz to 40 percent of
a. Internal Markers. The sweep generator pro-
center frequency. (Refer to para 3-5 for proper
vides internal markers at frequencies of 1, 10,
use of markers.)
and 100 MHz and all multiples of these frequen-
Note 1. phasing must be
readjusted (m, n, and o
cies within the range of the sweep generator.
above) whenever the SWEEP WIDTH control setting is
These markers are generated from a 5-megahertz
changed. If the specified maximum sweep width is not
obtained, adjust the WOBB DRIVE LIMIT potentiometer
tremely accurate. Separate amplitude controls are
clockwise until it is.
provided for each of the three sets of markers
Note 2. If the 1-MHz markers are not visible or if
to allow rapid identification of the frequency
they are off frequency, adjust the 1-MHz potentiometer
represented by an individual marker. Perform the
on the harmonic marker chassis so that nine 1-MHz
following operations and observe the actions of
markers appear between any pair of 10-MHZ markers.
r. Set the SWEEP WIDTH switch to NAR-
(1) Set up the sweep generator and oscil-
ROW and check the range of the SWEEP
range should be from 10 kHz to 1 MHz.
h.
s. Set the BAND SELECTOR switch to VHF.
(2) Set the SWEEP WIDTH switch at
t. Set the ATTENUATOR db switch to 0.
WIDE.
u. Set the SWEEP WIDTH control for maxi-
(3) Connect the RF OUTPUT jack of the
mum sweep width and adjust the phasing.
sweep generator through a 750-MHz resonant
v. Set the RF OUTPUT control fully clock-
circuit to one input jack of the D-50 detector.
wise; then slowly turn it counterclockwise until
Terminate the unused detector jack with Adapt-
the response trace flattens.
er-Connector UG-1640/U. Rotate the FRE-
QUENCY MEGAHERTZ knob for a center fre-
w. Check the range of the SWEEP WIDTH
quency of 750 MHz, which sets up a basic re-
control; it should be at least 10 kHz to 1 MHz.
sponse curve at 750 MHz. Observe the presenta-
x. Pull the 100 MHz MARKER GAIN switch.
y. Tune the sweep generator to 0 MHz.
z. Adjust the FIXED OSC FREQ screwdriver
(4) Increase the sweep width by rotating
adjustment on the front panel so that the 100-
the SWEEP WIDTH control until a narrow re-
MHz marker is just off the center of the zero
sponse curve presentation is observed similar to
beat.
(5) Push the PHASING TURN-BLANK-
Note. The instructions in z above tunes the fixed
ING PULL switch in and observe the return
oscillator just off 600 MHz. If the oscillator is tuned to
trace and a double set of markers.
precisely 600 MHz, its signal will mix with the sixth
harmonic of the 100-MHZ marker to generate an audio
(6) Rotate the PHASING TURN-BLANK-
beat signal which will distort the trace display.
ING PULL control until the top and bottom
aa. Set the SWEEP WIDTH switch to WIDE.
(7) Pull the PHASING TURN-BLANK-
ab. Adjust the SWEEP WIDTH control for
ING PULL switch out to blank out the return
maximum sweep width.
trace and the markers on it.
ac. Tune the sweep generator to position the
(8) Pull the 100 MHz MARKER GAIN
zero beat at the extreme left of the display.
switch/control and rotate it clockwise until
ad. Set the RF OUTPUT control fully clock-
markers are visible and resemble the response at
wise, then slowly turn it counter-clockwise until
the trace flattens.
(9) Observe that the peak of the response
ae. Using the 100-MHZ markers, verify that
curve is between two markers which can be iden-
the sweep width is at least 400 MHz.