10 Mhz Reference - HP 8560E Service Manual

6. The voltage at the R622/R623 node should measure approximately
−5 Vdc, biasing Q604 on.
7. If oscillator bias voltages are correct, place a 100 Ω resistor across
SAWR U602 input and output. If the SAWR has failed, this will
provide the equivalent loss of a correctly functioning SAWR, and the
circuit will begin to oscillate.

10 MHz Reference

The spectrum analyzer 10 MHz reference consists of 10 MHz OCXO
(Option 103: TCXO) with associated TTL level generator and
distribution circuitry. The OCXO (or TCXO) and TTL level generator
are turned off when an external 10 MHz reference is used. Also, with
the spectrum analyzer set to EXTernal frequency reference, U304A
output (low) forces the output of U304D to stay high. This allows
U304B to control the outputs of U303B, U304C, and U303D. In
INTernal frequency reference, U304D controls the outputs of these
three NAND gates, and the output of U304B is held high.
Check the 10 MHz reference by performing the following steps:
1. Set the HP 8560E/EC 10 MHz reference to internal by pressing
,
CTRL REAR PANEL
2. Use a spectrum analyzer to confirm the presence of a 10 MHz signal
at the following test points:
A15J303 .......................................................................... ≥−10 dBm
A15J304 .......................................................................... ≥−10 dBm
A15J301 .............................................................................≥−2 dBm
3. Check for a 1.3 V p-p waveform at A15J302 using an oscilloscope (see
Figure 11-3 on page
4. Check that the signal at A15J301 is 10 MHz ±40 Hz (with Option
103 TCXO reference) using a frequency counter. If necessary,
perform the appropriate 10 MHz reference adjustment.
5. If there is no problem with INTernal 10 MHz reference operation,
check EXTernal 10 MHz reference operation as follows:
6. Set the HP 8560E/EC 's 10 MHz reference to external by pressing
.
MHz EXT
7. Connect a 10 MHz, −2 dBm, signal to the rear panel 10 MHz REF
IN/OUT connector.
8. Check the signals at A15J301, A15J302, A15J303, and A15J304
according to the procedure in steps 2 through 4.
Chapter 11
, and .
10 MHz INT
604).
RF Section
A15 RF Assembly
AUX
10
603