Performance Verification; Audio Proof Of Performance Measurements; De-Emphasis Input Network - Crown FM30 User Manual

5.9 Performance Verification

Measure the following parameters to receive a comprehensive characterization of trans-
mitter performance:
• Carrier frequency
• RF output power
•
RF bandwidth and RF harmonics (see section 5.12)
• Pilot frequency, phase, and modulation percentage
• Audio frequency response
• Audio distortion
• Modulation percentage
• FM and AM noise
• Stereo separation between left and right
•
Crosstalk between main channel and subcarrier
• 38–kHz subcarrier suppression
• In addition to the above tests, which pertain to signal quality, a complete check of the
unit will include items listed in section 5.21.
5.9.1 Audio Proof-of-Performance Measurements
References to "100%" modulation assume 9% pilot and 91% for the remainder of the com-
posite stereo signal.
Because the audio processing threshold is at 90% modulation, it is not possible to make
audio proof-of-performance measurements at 100% modulation through the audio proces-
sor. Instead, data is taken at a level below the audio processing threshold at 80% modula-
tion.

5.9.2 De-emphasis Input Network

A precision de-emphasis network, connected between the test oscillator and the audio in-
put of the transmitter, can be very helpful when making the audio measurements. Note
that the input impedance of the transmitter or the source impedance of the test oscillator
can affect network accuracy. With the de-emphasis network, oscillator level adjustments
need only accommodate gain errors, instead of the whole pre-emphasis curve.
Adjustments and Tests 5-7