Viavi CX100 ComXpert Operation Manual page 191

Chapter 6 Performing Tests and Measurements
FM Transmitter Testing
10. RF Receiver
11. RF Receiver IF Bandwidth: select 12.5 kHz.
NOTE
To Calculate Proper Bandwidth
The UUT Transmitter Bandwidth can be determined with Carson's Rule (Sinusoidal
Tone):
The formula above provides the value, which in this example is 12 kHz, that is used to
determine the proper setting for the CX100 IF Bandwidth. In this example, the closest
CX100 IF Bandwidth greater than 12 kHz is 12.5 kHz IF Bandwidth, therefore, in this
example procedure, 12.5 kHz is selected for the CX100 RF Receiver IF Bandwidth.
AF Filter Selection
When the UUT is keyed, it generates a 67 Hz squelch tone. To determine the voice
modulation level and distortion, the 67 Hz tone must be filtered out so that only the
1 kHz test tone is received by the CX100 when measuring these parameters.
In this example, a Band Pass filter is selected so that frequencies lower than 300 Hz
will not be received by the CX100 Receiver, and frequencies higher than 3 kHz are
also blocked so as not to interfere with the 1 kHz test tone.
Rev 002
6 - 6
Demodulation
2 X [Maximum Deviation + Maximum Audio Frequency]
2 X [3 kHz + 3 kHz] = 12 kHz
CX100 ComXpert Operation Manual
Type: select FM.
22144015
August 2023