Chapter 11 555
Synthesizer Section
Unlocked YTO PLL
• Check the YTO DACs using the procedure in steps 41 through 49
below.
• Refer to steps 9 through 34 below.
8. If the YTO Frequency error recorded in step 5 is less than 20 MHz,
do the following:
• Measure the frequency at A14J304. The frequency should be
equal to the frequency recorded in step 6. If not, refer to
"Unlocked Fractional N PLL" in this chapter.
• Measure the input and output levels of the A15U100 sampler. If
the sampler appears defective, check the LO drive to the sampler
as described in "Sampler and Sampler IF."
• Refer to steps 34 through 51 below.
Check 1st LO
pretune
frequency and
amplitude (steps
9-12)
9. The pretuned frequency of the 1st LO must be sufficiently accurate
for the YTO loop to acquire lock. The amplitude of the 1st LO must
be sufficient to drive the A15U100 sampler. Perform the YTO
Adjustment procedure, particularly the YTO main coil adjustments.
(If available, use a synthesized microwave spectrum analyzer
instead of the microwave frequency counter specified in the
adjustment procedure.)
10.If the YTO main coil cannot be adjusted, proceed to step 33 to
troubleshoot the main coil coarse and fine DACs and main coil tune
DAC.
11.The front-panel 1ST LO OUTPUT should measure between +14.5
and +18.5 dBm in amplitude.
12.If the 1ST LO OUTPUT amplitude is out of the specified range,
perform the automated LOMA adjustments. Refer to Chapter 2.
Check the
fractional N
oscillator (steps
13-17)
13.Set the spectrum analyzer to the following settings:
Center frequency ..................................................... 300MHz
Span .................................................................................0Hz
14.Monitor the fractional N PLL output at A14J304 (FRAC N TEST)
with a synthesized spectrum analyzer such as an 8568A/B or
8566A/B. Refer to function block AI of A14 frequency control
schematic (sheet 4 of 5).
15.The signal at A14J304 (FRAC N TEST) should measure
approximately −10 dBm at 66.7 MHz. If the loop is unlocked, the
sampler IF frequency can also be seen on A14J304, about 30 dB
below the fractional N signal.
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