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External fm frequency response (alc on) – VXI 3002 User Manual

Page 88

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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.

ю

э

ь

о

н

м

FM1

2FM2

log

20

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.