HP 8560E, Service Manual

Page: 603 / 665

602 Chapter 11
RF Section
A15 RF Assembly
SIG ID Oscillator (Option 008)
See Function Block F of A15 RF schematic in the
HP 8560 E-Series
Spectrum Analyzer Component Level Informatio
n.
The SIG ID oscillator provides a shifted third LO (approximately 298
MHz) to distinguish true signals from false signals (such as image or
multiple responses). When the HP 8560E/EC is set to
SIG ID ON
, the
SIG ID oscillator turns on during alternate sweeps (Option 008
spectrum analyzers only).
1. Set the HP 8560E/EC to the following settings:
Trigger ................................................................ single sweep
SIG ID .................................................................................. on
2. Use an active probe with another spectrum analyzer to measure the
signal level at A15TP602.
3. On the HP 8560E/EC, press
SGL SWP
. With each press of
SGL SWP
,
the spectrum analyzer alternates between the following two states:
State 1:
A15J901 pin 13 (LSID) ......................................... TTL low
SIG ID oscillator............................................................ ON
Signal at A15TP602 298 MHz
±
50 kHz (at least +1 dBm)
State 1:
A15J901 pin 13 (LSID).........................................TTL high
SIG ID oscillator.......................................................... OFF
3rd LO driver amplifier .......... Provides LO for double balanced mixer
4. With the SIG ID oscillator on, measure the frequency at A15TP602
with a frequency counter and an active probe. If the frequency is not
298 MHz
±
50 kHz, refer to the "SIG ID Oscillator Adjustment"
procedure in Chapter 2. (There is no adjustment for instruments
with A15 RF assembly 08563-60084 or greater.)
5. On the HP 8560E/EC, press
SGL SWP
until A15J901 pin 13 is at TTL
low. Diodes CR603 and CR605 should be forward biased and CR604
should be reverse biased (approximately 6 Vdc reverse bias). Diodes
CR501 and CR502 should be forward biased, disabling the 3rd LO
driver amplifier.