Terrasat IBUC 2, Operation Manual

Page: 37 / 196

2-17
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Cyber Hardened IBUC
2
, IBUC
2e
, IBUC
2 G
, IBUC
R
, IBUC
G
Operations Manual: Functional Description
Engineered to Endure
Input to the IBUC also includes AC or DC voltage (via the J3 connector) and DC
voltage for low-power units. The input (L - band, 10 MHz, and DC via coaxial cable) is
routed to the demultiplexer circuitry where the various signals are split off and routed
to the appropriate circuits within the IBUC. (Only IBUCs with direct DC or AC via the
J3 connector feed the power supply directly.) The input voltage from the
demultiplexer circuitry is routed to the power supply and the FSK signal is routed to
the M&C card.
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 phase detector circuitry where it is compared with the phase
of the DRO (dielectric resonator oscillator) signal sample and consequently generates
a voltage that is applied as a control voltage to the DRO to adjust its frequency. The
DRO has been optimized for phase noise at a single frequency based on the frequency
band of that particular IBUC. The output of the DRO 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 DRO 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.
Frequency Stability vs. Operating
Temperature Range
(referenced to frequency at +25 °C)
- 30 ppb +30 ppb - 40 °C to +85 °C
Tuning Range
(referenced to nominal frequency)
±1 ppm ±1 ppm
Tuning Slope Positive
Table 2.9
Internal 10 MHz Reference Signal Parameters
Minimum Maximum Condition