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5-17
0 Hz (DC)
To measure the AM depth at DC, it will be necessary to use the DC offset facility on the function
generator proceeding as follows:
6960B
RF power meter
6912
Power
sensor
C2566
OUTPUT
Temporary
connection
SENSOR
INPUT
Function generator
DVM
RF
OUT
50
load
Ω
UUT
EXT MOD
INPUT
Fig. 5-9 0 Hz external AM and distortion test set-up
(9) Connect the test equipment as shown in Fig. 5-9.
(10) Set the function generator to +1.4142 V DC (temporarily connect the function generator
output to the DVM and set this voltage as close as possible to +1.4142 V).
(11) Measure the power on the power meter.
P1 _____
(12) Set the function generator to −1.4142 V DC (temporarily connect the function generator
output to the DVM and set this voltage as close as possible to −1.4142 V).
(13) Measure the power on the power meter.
P2 _____
(14) Subtract P2 from P1 (= x).
(15) Calculate the modulation depth using the formula:
ï
þ
ï
ý
ü
ï
î
ï
í
ì
(-x/20)
(-x/20)
10+1
10-1
= AM(%)
(16) Calculate the 0 Hz response relative to 1 kHz using the following formula, recording the
result in Table 5-35:
þ
ý
ü
î
í
ì
)15(inrecordedFigure
)6(inrecordedFigure
log20
10
(17) Set the UUT RF level to +7 dBm and repeat (10) to (16) using Table 5-36.
(18) Set the UUT RF level to +13 dBm and repeat (10) to (16) using Table 5-37.