3.If the signal at A15TP602 is low, but the signal at A15TP504 is correct, press [s),

INTERNAL MIXER,and SIG ID OFF.

4.Check that PIN diode switches CR603 and CR605 are reverse biased by approximately +10 Vdc. Refer to function block F of Al5 RF Schematic (sheet 1 of 3).

5.Measure 300 MHz signal at A15TP503 using an active probe/spectrum analyzer combination. If the signal is not approximately +lO dBm, refer to “Unlocked Reference PLL” in this chapter.

6.If the level at the TP503 is correct, but signal at TP504 is too low, the fault is probably in the amplifier.

Sampler and Sampler IF

The A15A2 Sampler creates and mixes harmonics of the sampling oscillator with the first LO. The resulting sampler IF (63 MHz to 105 MHz) is used to phase-lock the YTO. The Sampler IF filters unwanted products from A15A2’s output and amplifies the IF to a level sufficient to drive the YTO loop. When the IF is between 78 and 87 MHz, PIN diodes switch a 120 MHz notch filter in the sampler IF section.

1. Set HP 8560A to the following settings:

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

2.Disconnect W32 from A15JlOl.

3.Connect the input of a power splitter to A15JlOl. Connect W32 to one of the splitter outputs. Connect the other splitter output to the input of another spectrum analyzer.

4.If a 94.7 MHz signal, greater than -15 dBm, is not displayed on the other spectrum analyzer, set a microwave source to the following settings:

Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2107GHz Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -5 dBm

5.Connect the microwave source to A15A2Jl. A 94.7 MHz signal at approximately 0 dBm should be displayed on the other spectrum analyzer.

6.Use an active probe/spectrum analyzer combination to measure the signal at the following test points:

A15TPlOl

94.7 MHz, -25 dBm

A15TP201

294 MHz, +17 dBm

Synthesizer Section lo-45