Terrasat IBUC 3, Operation Manual

Page: 31 / 236

System Components
|
2-9
Engineered to Endure
The external 10 MHz reference signal is routed to the multiplier circuitry where its
level is first detected and an alarm issued if the signal is low. However, if the signal
level is low and the system is equipped with the optional internal 10 MHz signal, the
system will automatically switch to the internal 10 MHz signal. The 10 MHz signal is
then multiplied to the frequency used for phase-locking purposes. The output of the
multiplier is routed to the Synthesizer’s reference input. From this input, the signal is
processed and routed internally within the Synthesizer to the phase comparator
circuitry where the charge pump produces a control signal that will pass through a
loop filter and drive the VCO Core via the Vtune input. The output signal is then
automatically chosen from one of the multiple output stages. The Synthesizer has been
optimized for phase noise at multiple frequencies based on the frequency band of that
particular IBUC. The output of the Synthesizer is amplified and routed to the mixer.
The L - band signal that is split off in the demultiplexer circuitry is first filtered and a
sample of it detected for input power detection and control purposes. The signal is then
amplified, and goes through a variable attenuator. The attenuation is used to provide
an attenuation adjustment of 30 dB in 0.1 dB steps and to provide automatic level
control (ALC) or automatic gain control (AGC).
After additional amplification and filtering, the signal is routed to the mixer. The
L - band signal is then mixed with the Synthesizer signal to “upconvert” to the
appropriate RF signal based on the frequency band of the IBUC. The RF signal is
filtered, amplified, and then routed to the temperature compensation circuitry. The
temperature compensation circuitry has been calibrated so that the IBUC gain does not
vary more than 3 dB at any given frequency.
Note:
Some units can vary up to 4 dB at any given frequency.
The signal is then routed through an isolator to the solid-state power amplifier (SSPA).
Some models have an additional mechanical filter between the isolator and the SSPA.
The SSPA amplifies the signal which is then routed to the output through an isolator
for reverse power protection. The RF output is detected for M&C purposes. The IBUC
gain has been calibrated so that at minimum attenuation, a - 30 dBm input results in
rated power of at least P1dB at the output at any frequency or temperature, for GaAs
units. For GaN units the IBUC gain has been calibrated so that at minimum
attenuation, the small signal gain is, at a minimum, (P
SAT
+31)dB.
To operate at lower power levels, reduce the input to the IBUC or reduce the IBUC
gain by using the variable attenuator. Such feature is accessible through any of the
M&C interfaces. The output of a Ku - band IBUC is a WR75 cover with groove
waveguide.
Figure 2.2 depicts the signal flow for units that are DC powered low energy
consumption units, while Figure 2.3 depicts the signal flow for units that are DC
powered.