Crown Low Power Transmitters - Crown Broadcast

5.2.3 19–kHz Level
Adjust the 19–kHz pilot for 9% modulation as indicated on an FM modulation
monitor.
(The composite output should be set first, since it follows the 19–kHz Level
control.)
5.2.4 19–kHz Phase
1. Apply a 400–Hz audio signal to the left channel for at least 70% modulation.
2. Look at the composite stereo signal at TP301 on the RF Exciter circuit board
with an oscilloscope, expanding the display to view the 19–kHz component
on the horizontal centerline.
3. Switch the audio to the right-channel input. When the 19–kHz Phase is
properly adjusted, the amplitude of the 19–kHz will remain constant when
switching between left and right.
4. Recheck the separation adjustment as described in section 5.2.1.
5.3 Frequency Synthesizer Adjustments
5.3.1 Frequency (Channel) Selection
Refer to section 2.3.
5.3.2 Modulation Compensator
Refer to section 2.3.
5.3.3 Frequency Measurement and Adjustment
Next to the 10.24–MHz crystal on the RF Exciter board is a 5.5–18 pF ceramic
trimmer capacitor (C307). Use C307 to set the frequency of the 10.24–MHz crystal
while observing the output frequency of the synthesizer.
Use one of two methods for checking frequency:
❑
❑
Use an FM frequency monitor.
Couple a frequency counter of known accuracy to the output of the synthesizer
and observe the operating frequency.
5–4 FM30/FM100/FM250 User's Manual