HP 8560A, Service Manual

Page: 351 / 450

Table 10-2. Sampling Oscillator Test Frequencies
HP 8560A HP 8340A Frequency of Offset
Frequency (MHz) CW Frequency (MHz) Sampling Oscillator (MHz)
389.5
4300.2 280.0
427.0 4337.7 282.5
449.5
4360.2 284.0
464.5 4375.2 285.0
479.5 4390.2
286.0
502.0 4412.7 287.5
509.5
4420.2 288.0
539.5
4450.2
290.0
569.5
4480.2
292.0
577.0 4487.7
292.5
599.5
4510.2
294.0
614.5 4525.2
295.0
629.5
4540.2
296.0
652.0 4562.7
297.5
659.5
4570.2
298.0
Troubleshooting Test Setup
Some Synthesizer Section problems require placing the YTO PLL in an unlocked condition.
This is done by moving jumper A14J23 to the TEST position. This grounds the YTO LOOP
ERROR signal, disabling the CPU’s ability to detect an unlocked YTO. The FM Coil Driver’s
output is set to its mid-range level causing the YTO to be controlled only by the Main Coil
Tune DAC.
Synthesizer Section troubleshooting is best done with the HP 8560A’s SPAN set to 0 Hz (even
though it is still possible to sweep the Main and FM coils of the YTO).
With the YTO in its unlocked conditions and the SPAN set to 0 Hz, the nominal YTO
frequency is not necessarily the value listed as LO FREQ in the Frequency Diagnose menu.
The YTO has an initial pretune accuracy of MHz, but this pretune accuracy shifts
MHz as a function of the Sampler IF frequency. This enables the YTO loop to acquire
lock when the Sampler IF is near its extremes. As a result, the nominal YTO frequency also
shifts
MHz depending on the Sampler IF frequency.
The Roller Oscillator frequency is the same as the desired sampler IF. Table outlines
the changes in YTO pretune accuracy and nominal YTO frequency as a function of Roller
Oscillator frequency.
n
To display the Roller Oscillator’s frequency press
(CAL), MORE, FREQ DIAGNOSE ,
MAIN ROLLER.
If the Sampler IF is negative (YTO frequency is lower than the desired
Sampling Oscillator harmonic), the Main Roller frequency will be displayed as a negative
number.
Synthesizer Section 10-7