HP 8560E - Page 545

544 Chapter10
Synthesizer Section
Unlocked YTO PLL
25.The sampler IF should measure between 46 MHz and 86 MHz at −15
dBm to +2 dBm. If the signal frequency or amplitude is incorrect,
refer to "Unlocked Offset PLL" in this chapter.
26.Set jumper A14J23 in the NORMAL position. Reconnect W32 to
A15J101.
Check FM loop sense (steps 28-34)
27.Set jumper A14J23 in the TEST position.
28.Set the HP 8560E/EC to the following settings:
Center frequency ..................................................... 300MHz
Span .................................................................................0Hz
29.Connect an RF signal-generator output to A14J501. Set the signal
generator to the following settings:
Frequency .................................................................. 56MHz
Amplitude .................................................................... 0dBm
30.Monitor A14J17 pin 1 with a DVM or oscilloscope. Connect ground to
A14J17 pin 6.
31.As the signal generator frequency is increased to 76 MHz, the
voltage at A14J17 pin 1 should change from approximately +12 V to
−12 V.
32.Set the signal generator to the following settings and repeat step 30.
Frequency .................................................................. 56MHz
Amplitude ................................................................ −15dBm
33.If the voltage monitored in step 30 is correct with a 0 dBm output
but not with −15 dBm output, suspect the limiting amplifier function
block AE.
34.Place jumper A14J23 in the NORMAL position and reconnect W32
to A14J501.
Check YTO FM coil driver and main loop error voltage driver
(steps & 35-40)
35.To troubleshoot the YTO FM coil driver, refer to step 6 of "First-LO
Span Problems (2.01 MHz to 20 MHz)."
36.Steps 36 through 40 verify that the YTO-loop error voltage is
reaching the FM coil. The main loop error voltage driver has a gain
of either 1.5 or 15; the spectrum analyzer firmware controls the gain
during the locking process. The error voltage is read by the ADC on
the A3 interface assembly. A14U326D calibrates out any offsets from
true ground. A14U326A inverts the sense of the YTO loop to lock the
YTO on lower sampler-sidebands (YTO frequency < (sampler
frequency × sampler harmonic)). The fractional N frequency