HP 8560A Unlocked Roller Oscillator PLL

Unlocked Roller Oscillator PLL

Operation

The Roller Oscillator is used in the HP 8560A as a reference for the 1st LO phase-lock loop. It provides the 25 Hz start-frequency resolution for the 1st LO, and is the means by which the 1st LO is swept in LO spans of 1 MHz or less (Roller spans). It is composed of the following three separate phase-lock loops:

Offset Oscillator PLL

Transfer Oscillator PLL

Main Oscillator PLL

These three PLLs operate together to produce an output frequency in the range of 65 MHz to 104 MHz selectable in 25 Hz increments. The output frequency can be swept (increasing or decreasing) over a selectable 2.5 kHz to 1 MHz range.

To determine the Roller frequency for any given center frequency, press (CAL), MORE ,

FREQ DIAGNOSE, and MAIN ROLLER. The MAIN ROLLER frequency displayed is the frequency that will be measured at A14J304 ROLLER TST with the HP 8560A in zero span.

Note	Because the three Roller loops are all interdependent, an error message
	displayed on screen might not be the primary cause of the failure. Be sure to
	query the error message buffer for all encountered errors by pressing [m),
	MORE, RECALL ERRORS and using the knob or step keys to scroll through all
	encountered errors. The frequency displayed for the Offset Roller using the
	above procedure is the Offset Roller frequency/loo.

During the LO ADJUST sequence performed at power-on, pretune-DAC-values for Roller Oscillator frequencies, spaced 2 MHz apart, are determined and stored. Pretune-DAC-values for frequencies locked during instrument operation are interpolated from these calibration values. Tuning sensitivities for the Main and Offset Rollers are determined and used to adjust the Roller Span Attenuator DAC U114B to improve span accuracy.

Confirming an Unlocked Condition

1. Set the HP 8560A to the following settings:

CENTER FREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .300 MHz SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 Hz

2.Connect A14J304 ROLLER TST to the input of a synthesized spectrum analyzer and view the Roller Oscillator output at 94.7 MHz.

Note	If a synthesized spectrum analyzer is not available, connect A14J304 to the
	input of a 20 dB gain amplifier, such as an HP 84473. Connect the output of
	the amplifier to the input of a frequency counter.

lo-32 Synthesizer Section