Reference Level Accuracy - Tektronix 7L5 Instruction Manual

h. Add 10 dB of external attenuation. Adjust the VAR
control for a signal display amplitude of 8 divisions.
i. Add 6 dB of external attenuation. Verify that the
signal amplitude decreases to 4.0 ±0.2 division (±5%) or
half amplitude.
j. Add an additional 6 dB of external attenuation and
verify that the display amplitude decreases to 2.0 ±0.1
division.
VARiable Control Range
k. Insert 10 dB of external attenuation. Select the
2 dB/DIV pushbutton and rotate the VAR control fully cwo
Adjust the REFERENCE LEVEL to set the displayed signal
amplitude to a vertical reference point near full screen.
I. Rotate the VAR control fully ccw (detent position).
Verify that the signal amplitude decreases at least 4.0
divisions. Decrease external attenuation to return the
signal amplitude to the reference point and verify that the
required change was 8 dB or more.
4. Reference Level Accuracy (within 0.2 dB/dB with
a cumulative error not to exceed 0.25 dB for any
change up to 10 dB)
The external 'attenuator accuracy requirements to
perform this step, have been described in the Introduction
to this Operational Check procedure. Reference level
increments are 1 dB and 10 dB steps. Circuitry of the 7L5
provides 1, 2, 4, 8, and 16 dB gain steps. These steps, or
combinations of the steps, provide the reference level
range. This procedure checks the accuracy of each gain
cell and thus the overall accuracy. The accuracy of the
V /Div mode will be within that specified if the Log mode
reference level is within limits. A few check points may be
performed as listed in Table 3-4 to spot check Lin mode
operation.
This procedure uses a 50 0 plug-in module (L 1):
a. Switch the dBm/dBV selector (on the plug-in
module) to dBm and set the 7L5 controls as follows:
REFERENCE LEVEL -29 dBm
RESOLUTION 3 kHz
FREQEUNCY SPAN/DIV 1 kHz
TIME/DIV AUTO
b. Set the external attenuation to 2 dB and adjust the
REFERENCE LEVEL for a readout of -29 dBm. Adjust the
VERT POSITION control slightly, as required to establish
a graticule reference point for the signal peak.
@
Operating Instructions-7L5 Operators
c. Change the REFERENCE LEVEL control to
-30 dBm. Increase the external attenuation 1 dB (3 dB
total) and verify that the signal peak is within 0.2 dB of the
reference point established in step b.
d. Rotate the REFERENCE LEVEL control to
-31 dBm. Increase the external attenuation another 1 dB
(4 dB total) and verify that the signal peak is within 0.25 dB
of the reference pOint.
e. Readjust the VERT POSITION control, as required,
to establish a new graticule reference point for the signal
peak.
f. Pull the REFERENCE LEVEL control out to the
10 dB/step position and set it for a crt readout of
-41 dBm. Increase the external attenuation 10 dB (14 dB
total) and verify that the signal level is within 0.25 dB of the
reference point established in step e.
g. Check the Reference Level accuracy for the remain-
ing range by following the settings listed in Table 3-3 and
noting the error.
TABLE 3-3
Reference Level External Attenuation Allowable Limits
(dBm) (dB) (dB)
-41
14
0.25
-51 24 0.50
-61
34 0.75
-71
44
1.00
-81
54
1.25
-91
64
1.50
-101
74 1.75
-111
84 2.00
-121
94 2.25
LIN Accuracy
g. Set the external attenuator to 0 dB. Select the LIN
pushbutton and adjust the REFERENCE LEVEL control
for a crt readout of 10 mV.
h. Set the external attenuator and the REFERENCE
LEVEL control to the positions listed in Table 3-4. Check
that the measured signal amplitudes are in accordance
with those listed in Table 3-4.
3-11
Scans
by O"tso",ce-Optio1ls
=>