YTO FM Coil Span Problems (LO Spans 1.01 MHz to 20 MHz)

In YTO FM Coil spans, the YTO loop is locked and then opened while the sweep ramp is summed into the FM coil. FM spans are adjusted by changing the sensitivity of the FM coil driver.

1.Perform the YTO Adjustment procedure in Chapter 2. If the YTO adjustments cannot be performed, continue with this procedure.

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

C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. 300 MHz

SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

..20 MHz

SWEEPTIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . 5 0 m s

3.Check for the presence of a 0 V to -10 V sweep ramp at A14J15 pin 14 (input to the Main/FM/VCO/Sweep Switch). Refer to function block G of Al4 Frequency Control Schematic (sheet 2 of 5).

4.Check for the presence of a 0 V to +5 V sweep ramp at A14U405 pin 6 (YTO FM Coil Driver). Refer to function block N of Al4 Frequency Control Schematic (sheet 2 of 5).

5.Check the state of the Main/FM/VCO S weep Switches as indicated in Table 10-8.

6.The rest of the procedure troubleshoots the YTO FM Coil Driver. Refer to function block N of Al4 Frequency Control Schematic (sheet 2 of 5).

Table 10-8. Settings of Sweep Switches

I

Switch

Switch State

 

 

Switch Control Line

Control Line State

 

I

 

 

(Pin #)

PTL)

 

U318A

Open

1

High

 

U318C

Open

9

High

 

U318D

Closed

16

Low

 

U324A

Closed

1

High

 

U324B

Closed

8

High

 

U324C

Open

 

 

9

Low

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

 

C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. 300 MHz

SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . OHz

TRIG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. SINGLE

8.On the HP 8560A press ISAVE), SAVE STATE, STATE 0.

9.Remove jumper A14J23 and connect a dc voltage source to A14J23 pin 2.

10.Connect a microwave frequency-counter or spectrum analyzer to the HP 8560A’s 1ST LO OUTPUT.

11.Set the dc-voltage source’s output for 0 Vdc and note the 1st LO frequency.

12.Set the dc-voltage source’s output for +lO Vdc. The 1st LO frequency should increase approximately +15.6 MHz.

Synthesizer Section lo-17