Comtech EF Data KST-2000A/B - Manual (Page 70)

Ku-Band Satellite Transceiver Revision 9
Operation MN/KST2000AB.IOM
3–22
3.7 Reference Oscillator
The reference oscillator assembly (Figure 3-12) consists of a high stability, 10 MHz,
Oven Controlled, Voltage Controlled, Crystal Oscillator (OCVCXO), a 72 MHz oscilla-
tor, and a micro-controller.
Figure 3-8. Reference Oscillator
The reference oscillator assembly can accept an external 5 or 10 MHz input signal
≤ +6
dBm. The reference oscillator has an onboard phase detector which is used to frequency
lock the 10 MHz oscillator to the external reference. A bias voltage output from the phase
detector is read into the microcontroller via an A to D converter. The
microcontroller interprets this bias voltage and generates a tuning voltage output propor-
tional to the phase/frequency difference between the onboard oscillator and the external
reference input. This output is applied to the tuning voltage input on the OCVCXO to
shift its operating frequency to maintain frequency lock with the external input.
The 10 MHz OCVCXO is a high stability, low phase noise, crystal oscillator. It has a tun-
ing voltage input which can be used to fine tune the oscillator frequency. When the
KST-2000A/B is operating without an external 5 or 10 MHz input, the M&C generates a
bias voltage which can be changed remotely. That sets the oscillator frequency.
When an external reference is applied, the KST-2000A/B will generate a bias voltage of
sufficient level to keep the 10 MHz reference frequency locked to the external input. The
10 MHz output is amplified and distributed to the down converter, where it is the refer-
ence for the DROs. It also serves as the reference frequency for the 72 MHz oscillator.
The 72 MHz VCXO is phase locked to the 10 MHz reference. The 72 MHz output of the
VCXO is amplified and distributed throughout the KST-2000A/B to provide a reference
frequency for the up converter and portions of the down converter.
PHASE
DETECTOR
MICRO
CONTROLLER
FAULT /
STATUS
10 MHz OCVCXO
72 MHz
GENERATOR
I2C
EXTERNAL
REFERENCE