Model 1415A Section I11
Paragraphs 3- 1 to 3-14
SECTION 111
OPERATION
amplitude of 10 cm at X1. Calibration of the reflection
3-1. INTRODUCTION.
coefficient assumes a 50-ohm external system. The
3-2. This section contains informationon the function VERNIER control provides variable adjustment between
of all controls in the Model 1415A Time Domain Re-
steps.
flectometer and on the basic operation of the instru-
ment. Refer to the oscilloscope manual for instruc-
tions on operating CRT display controls. 3-10. OPERATION.
3-11. GENERAL. Figures 3-2 through 3-6 give
3-3. CONTROLS AND CONNECTORS. step-by-step procedures for operating the Model
1415A. The vertical andhorizontal calibration adjust-
3-4. Figure 3-1 identifies and briefly describes the
ments should be done whenever the Model 1415A is
Model 1415A controls and connectors. To aid in operated in an oscilloscope other than the one in
proper operation, Paragraphs 3-5 through 3-9 pro-
vide a more extensive description of some controls. which it was previously adjusted; this includes first-
time operation. Aperiodic check of these adjustments
3-5. DISTANCE/TIME CM LINE/CM DISPLAY. is also recommended even when the Model 1415A is
The four settings on this switch are calibrated both used in only one oscilloscope.
in nanoseconds per centimeter, and in centimeters
3-12. ELIMINATION OF RF INTERFERENCE. The
of external transmission line per centimeter of dis- CRT display may become distorted dub to RFI when
play. Values are indicated for the two most common
the instrument is used to test antennas or long trans-
types of transmission line, polyethylene dielectric missionlines, since these elements tend to act as re-
(black numerals) and air dielectric (red numerals).
ceiving antennas for any RF in the area. When a
3-6. DISTANCE/TIME MAGNIFIER. The eight set- narrow band RFI problem exists, it can be eliminated
tings on this switch indicate horizontal display magni- by adjustingthef, (interference filter center frequency)
fication from X1 to X200. These settings are used control. If the RFI is of a broad band nature, the f,
as division factors for DISTANCE in CM LINE/CM control is adjusted for minimum interference, then
DISPLAY or for TIME in NSEC/CM. The display the BW (interference filter bcndwidth) control is
expands around the point selected by the MAGNIFIER adjusted for further elimination of the interference.
DELAY control, which is indicated by a brightened Normally, the instrument is operated with the BW
spot on the display. control in the MAX position. If the BW control is
adjusted away from the MAX position, the Model
3-7. MAGNIFIER DELAY. This 10-turn potentio-
meter is calibrated in tenths of millimeters from 0 1415A must be switched to the DETAIL mode of opera-
tion to avoid seriously degrading the vertical presenta-
to 10 centimeters, and uses a brightened dot on the tion. These effects are quite obvious when viewing
display as an indicator; e. g., dot is midscreen with
the CRT presentation. In addition, a shorter and
MAGNIFIER DELAY set at 5.00 centimeters. The shorter time scale setting is required as the BW con-
reading on the control is used to calculate distance
trol is turned towards minimum if no degrading of the
or time in conjunction with the basic DISTANCE/TIME vertical presentation can be tolerated. This is not a
setting only, but is independent of the DISTANCE/ serious limitation, since any portion of the longer
TIME MAGNIFIER setting.
time scale can be observed by adjusting the magnifier
3-8. SWEEP. Horizontalscan modes of the instrument and delay controls.
are selected by this five position switch as follows:
RECORD position provides the signal to drive an ex-
ternal recorder through the RECORDER OUT jacks; 3-1 3. APPLICATIONS.
RESET position resets the recorder sweep to zero;
MANUAL position sets up the MANUAL SCAN control 3-14. The Model 1415A has beendesignedspecifically
for time domain reflectometry, a measurement tech-
for manual scanning of the input signal (also helpful
for calibrating the external recorder); NORMALposi- nique offering the most convenient method for gaining
valuable information on most types of transmission
tion is used for normal scanning of the input signal line systems. To describe this technique and its
(about 3000 samples per sweep, repetition rate of 50
applications, @ ApplicationNotes 62 and 67 have been
cps); and DETAIL position which provides a higher prepared. These application notes discuss the funda-
sampling density for a more detailed sweep (about
30,000 samples per sweep, repetition rate of 5 cps). mentals of transmission line measurements, and give
practical measuring conditions. Application Note 67
3-9. REFL COEFFICIENT (VERTICALMAGNIFIER). also contains additional information concerning the
Vertical scale of the instrument is determined by this impedance overlays which are located inside the back
control as follows: directly in reflection coefficient cover of this manual. The user is referred to these
reading per centimeter; or (in parenthesis) in vertical publications. Copies may be obtained from your
magnification fromXO. 2 toX20, referenced to a step Hewlett- Packard Sales/Service Office.
01944-3 3- 1 |
ACEC
