Common-Mode Rejection Ratio; Channel Isolation - Tektronix 2246 1Y Service Manual

Performance Check Procedure—2246 1Y and 2246 Mod A Service

20. Common-mode Rejection Ratio

a. Connect leveled sine-wave generator (SG 503)
output to the CH 1 and CH 2 input connectors via
a 50-X1 precision BNC coaxial cable, a 50-11
BNC termination, and a BNC dual-input coupler.
b. Set the leveled sine-wave generator output for
an eight-division signal-display amplitude at
50 kHz.
c. Set:
ADD MODE
CH 2 VOLTS/DIV
CH 2 INVERT
CH 1 Vertical MODE
SCOPE BW
d. Adjust CH 1 or CH 2 VAR VOLTS/DIV for smallest
signal amplitude (as needed).
e. Set the leveled sine-wave output frequency to
10 MHz.
f. Set:
CH 1 Vertical MODE
ADD MODE
g. Set the leveled sine-wave output amplitude for
an eight-division display.
h. Set the Vertical MODE to ADD (CH 1 off).
i. CHECK—the signal is less than 0.3 division in
amplitude.
j. Set the leveled sine-wave generator frequency
to 100 MHz.
k. Set VERTICAL MODE to CH 1 (ADD off).
. Set the leveled sine-wave output amplitude for
l
an eight-division display.
m. Set the VERTICAL MODE to ADD (CH 1 off).
n. CHECK—the signal is less than 0.8 division in
amplitude.
o. Disconnect the test setup.
p. Set both CH 1 and CH 2 VAR controls to their
calibrated (fully clockwise in detent) positions.
q. Disconnect the test setup.
4-12

21. Channel Isolation

a. Set:
Vertical MODE
CH 2 INVERT
CH 1, CH 2, CH 3, and CH 4
VOLTS/DIV
Trigger SOURCE
b. Connect the leveled sine-wave generator (SG
503) output to the CH 1 input via a 5 0 - fi pre­
cision BNC coaxial cable and a 5 0 -fl BNC
On
termination.
10 mV
On
c. Set the leveled sine-wave generator (SG 503)
Off
output for a five-division signal display amplitude
Off
at 100 MHz.
d. Set CH 2, CH 3, and CH 4 Vertical MODE On
(CH 1 off).
e. CHECK—display amplitude is 0.1 division or less,
excluding trace width, on the CH 2, CH 3, and
CH 4 traces.
f. Move sine-wave generator signal to the CH 2
input.
On
Off
g. Set:
CH 1, CH 3, and
CH 4 Vertical MODE
Trigger SOURCE
h. CHECK—display amplitude is 0.1 division or less,
excluding trace width, on the CH 1, CH 3, and
CH 4 traces.
i. Move sine-wave generator signal to the CH 3
input.
j. Set:
CH 1, CH 2, and CH 4
Vertical MODE
Trigger SOURCE
k. CHECK—display amplitude is 0.1 division or less,
excluding trace width, on the CH 1, CH 2, and
CH 4 traces.
. Move sine-wave generator signal to the CH 4
l
input.
m. Set:
CH 1, CH 2, and CH 3
Vertical MODE
Trigger SOURCE
CH 1 and CH 2
(ADD off)
Off
0.1 V
CH 1
On (CH 2 off)
CH 2
On (CH 3 off)
CH 3
On (CH 4 off)
CH 4