41.The Main Coil Coarse and Fine DACs correct any initial pretune errors in the YTO main coil. The DACs adjust the FM-coil current to zero before any sweep begins. Refer to function block I of Al4 Frequency Control Schematic (sheet 2 of 5).

42.Set the HP 8560A to the settings listed below. These set both DACs to 128 (the DAC setting range is 0 to 255).

C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz TRIG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..CONT

43. Verify the voltages listed in Table 10-14.

Table 10-14. Main Coil Coarse and Fine DACs Voltages

Measurement Points

Voltages

A14J17 pin 2

-7.0

Vdc

A14J17 pin 3

-7.0

Vdc

A14J17 pin 5

+8.1 Vdc

 

 

 

44. Place jumper A14J23 in the NORMAL position.

Note

The All YTO has an initial pretune accuracy of f20 MHz. However, when

 

the Roller Oscillator frequency is <73 MHz this is changed to +30/-10 MHz.

 

If the Roller Oscillator frequency is >93 MHz, the accuracy is changed to

 

+lO/-30 MHz. This is done by changing the Main Coil Coarse DAC to keep

 

the Sampler IF within the acquisition range of the YTO Loop. When dealing

 

with the Sampler IF and an unlocked YTO, the same frequency differences

 

apply to the Sampler IF.

 

 

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

C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300MHz SPAN . . . . . . . . . . . . . . . . . . . . . :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 Hz

46.Place jumper A14J23 in the TEST position.

47.Measure the output of the Main Coil Tune DAC (A14J18 pin 3) with a DVM. Refer to function block C of Al4 Frequency Control Schematic (sheet 2 of 5) in the Component-Level Information binder.

48.If the HP 8560A’s center frequency is 300 MHz, the voltage at A14J18 pin 3 should measure -3.35 V 60.25 V. The voltage may also be determined from the following equation:

V= -(lst LO Frequency-2.95 GHz)x2.654V/GHz

49.The voltage at A14U330 pin 2 should measure 3.4 V f0.2 Vdc. This represents a current setting the YTO to approximately 2.95 GHz.

Synthesizer Section 10-31