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5-13
(5) On the modulation meter check that the FM reading is between 47.5 kHz and 52.5 kHz, then
set a reference using the relative function.
(6) Set the function generator to each of the frequencies shown in Table 5-25 checking that the
relative readings on the modulation meter are within specification.
(7) At those frequencies indicated in Table 5-25, set the modulation meter LF output control to
mid-position and measure the AF distortion on the audio analyzer, checking that the results
are within specification.
0 Hz (DC)
To measure the FM deviation at DC, it will be necessary to use the DC offset facility on the
function generator proceeding as follows:
(8) 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).
(9) Press CARRIER ERROR on the modulation meter.
(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 frequency indicated on the modulation meter carrier frequency window.
FM1 _____
(12) Reset the function generator to 1V RMS, 1 kHz sine wave and measure the FM deviation.
FM2 _____
(13) Using the following formula, calculate the change in response checking that the result is
within the specification shown against 0 Hz in Table 5-25.
þ
ý
ü
î
í
ì
FM1
2FM2
log20
10
External FM frequency response (ALC on)
Test procedure
(1) Connect the test equipment as shown in Fig. 5-8.
(2) On the UUT set:
Carr Freq 15 MHz
RF Level 0 dBm
Mod Mode FM External
FM1 Level 10 kHz
Source On
Mod On
ALC coupling
(3) Set the function generator to give 0.75 V RMS, 1 kHz sine wave.
(4) On the modulation meter select CAL, FM, 10 Hz
Þ 300 kHz filter.
(5) On the modulation meter check that the FM reading is between 9.5 kHz and 10.5 kHz, then
set a reference using the relative function.
(6) Set the function generator to each of the frequencies shown in Table 5-26 checking that the
relative readings on the modulation meter are within specification.
(7) Set the function generator to 1.25 V RMS and repeat (4) to (6) using Table 5-27, also
measuring the AF distortion on the audio analyzer at those frequencies indicated.