Comtech EF Data SMS-458B - Manual (Page 81)

SMS-458B Modem Protection Switch Revision 2
Theory of Operation MN/SMS458B.IOM
4–21
4.6 IF Switch
4.6.1 General
The IF switch (Figure 4-9) is a 14.0 x 5.0 inches module that fits in the lower section of
the switch chassis. It isolates the backup modulator’s IF outputs and connects the backup
modulator’s output in place of any of the prime modulators when a fault is detected. It
also connects the IF backup demodulators inputs to one of four downlink inputs.
There are two IF switch cards in the switch:
• One for transmit switching.
• One for receive switching.
4.6.2 Specifications
Power source +12V
Isolation ≥ 60 dB
Balance ± 0.25 dB
Loss ≤ 1 dB
4.6.3 IF Switch Theory of Operation
The IF switch contains 22 baseball switches that comprise the IF switching matrix. Each
baseball switch is controlled separately by the M&C card via the switch driver card.
The modulator section of the switching matrix contains 16 of the switches that control the
backup modulator outputs to switch to any of the eight prime modulator outputs if a fault
is detected by the M&C card. The operator can also manually select a backup modulator
to switch in for any of the prime modulators via the front panel (refer to Section 3.1 and
3.4.5.3).
The demodulator section of the switching matrix contains the remaining six switches.
They connect the IF backup demodulator inputs to any of four downlink inputs for use
when any of the prime demodulators are faulted. The operator can also manually select a
backup demodulator to be online for any of the prime demodulators via the front panel.
Note: Only four prime modems may be used with this switch.