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A9 Input Attenuator
The attenuator is a
500
precision, coaxial step attenuator. Attenuation in 10 dB steps from
0 dB to 70 dB is accomplished by switching the signal path through one or more of the three
resistive pads. The attenuator automatically sets to 70 dB when the spectrum analyzer turns
off, providing ESD protection. (Note that the input attenuator is not field-repairable.)
A fourth attenuator section switches a blocking capacitor in and out.
A10 YIG-Tuned Filter/Mixer
The YIG-tuned filter/mixer (RYTHM)
is a combination of an RF switch, a high band mixer,
and a tracking preselector. The PIN diode switch directs the RF input to the appropriate
mixer in the A10 RYTHM assembly or A8 low band mixer.
The tracking preselector is a YIG-tuned filter. It functions as a tunable
bandpass
filter for
high band signals. Coarse frequency control originates from slope and offset DACs located on
the Al4 frequency control assembly. (Slope and offset DAC values are loaded into EEROM.)
Fine frequency control originates from a preselector peak DAC located on the A3 interface
assembly. Values for the preselector peak DAC are interpolated approximately every 17 MHz
based upon data taken during the frequency response (flatness) adjustment. The preselector
bandwidth varies from greater than 30 MHz, at 2.75 GHz, to greater than 40 MHz, at
13.2 GHz.
The high band mixer is ac coupled. It uses the first and second harmonics of the first local
oscillator to cover the frequency range. A PIN diode switch in A7 SLODA directs the first LO
to the appropriate mixer. The Al4 frequency control assembly provides PIN diode bias.
All YTO
All is a YTO (YIG-tuned oscillator). YIG (yttrium-iron-garnet) is a ferro-magnetic material
which is polished into a small sphere and precisely oriented in a magnetic field. Changes in
this magnetic field alter the frequency generated by the YTO. Current control of the magnetic
field surrounding the YIG sphere tunes the oscillator to the desired frequency.
Al3 Second Converter
The Al3 second converter down-converts the 3.9107 GHz first IF to a 310.7 MHz 2nd IF.
In high band, it passes the 310.7 MHz first IF from the A10 YIG-tuned filter/mixer to the
Al5 RF assembly. The converter generates a 3.6 GHz second LO by multiplying a 600 MHz
reference.
Bandpass
filters remove unwanted harmonics of the 600 MHz driving signal. First
IF and 2nd LO signals are filtered by cavity filters.
Second IF Amplifier (part of A15)
The second IF amplifier (SIFA) amplifies and filters the second IF. Access to this pre-filtered
signal is available at the rear-panel 2ND IF OUTPUT (Option 001 only).
The external mixing input from the front-panel IF INPUT connector is also directed through
the SIFA. A dc bias is placed onto the IF INPUT line for biasing external mixers.
7-44 General Troubleshooting