Chapter 12 615
RF Section
A14 Frequency Control Assembly
Control Latch for Band-Switch Drivers
Refer to function block P on A14 Frequency Control Schematic Diagram
in the 8560 E-Series Spectrum Analyzer Component Level Information.
1. Connect the positive lead of a DVM to A14U417 pin 14
(LLOWBAND) and the negative lead to A14J18 pin 6.
2. Set the spectrum analyzer to the following settings:
Center frequency .................................................. 300MHz
Span .............................................................................. 0Hz
3. The voltage should measure approximately 0 Vdc (TTL low).
4. Set the spectrum analyzer center frequency to 3 GHz.
5. The voltage should measure approximately +5 Vdc (TTL high).
6. Move the positive lead of the DVM to A14U406 pin 12 (LSBTX).
7. The voltage should measure approximately +5 Vdc (TTL high).
8. Set the spectrum analyzer center frequency to 35 GHz.
9. The voltage should measure approximately 0 Vdc (TTL low).
YTF Driver Circuit
The YTF driver circuitry consists of the Sweep + Tune Multiplier, FAV
(Frequency Analog Voltage) Generator, YTF Gain and Offset, and YTF
Drive. Refer to function blocks Q, R, S, and T on A14 frequency control
schematic diagram. The FAV generator generates the 0.5 V/GHz signal.
The YTF driver circuitry can be half-split by checking the rear panel
FAV OUTPUT.
NOTE The rear panel output changes according to the external-mixer mode
selected. The preselected external-mixer mode must not be selected
while executing this procedure. Make sure that the rear panel output is
set for .50 V/GHz and not .25 V/GHz.
The Sweep + Tune Multiplier takes tune information (YTO start
frequency) and sweep (based on LO span) and multiplies it so that it is
correct for the appropriate YTF band.
C31 of the FAV Generator holds the YTF steady during retraces
between multiband sweeps. Switch U606C and R94 provide the YTF
dehysteresis pulse. A dehysteresis pulse is activated at the end of spans
greater than 1 MHz. In microwave bands, amplifier U402A provides an
offset voltage to account for the 310.7 MHz offset (U415A open) between
the desired harmonic of the YTO frequency and the center frequency. In
low band, switch U415A is closed to account for the negative
3.9107 GHz 1st IF offset between the YTO frequency and the center
frequency. In millimeter bands, U415D is closed to account for the
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