Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Page
6-21
Section 6 Theory of Operation
Issue 1.1
6.5.4 NDB Site Interface PWB
(Optional)
See Figures SD-14 and 15. The NDB site
interface PWB (A4), if purchased, provides:
x
16 optically isolated monitor inputs.
x
16 form C contact relay closure control
points.
6.5.4.1 Site Monitor Points
RFI filtering is provided on all control input
lines to ensure transmitter operation is not
interrupted due to RF pick-up on control lines.
Opto-couplers buffer/isolate the external
circuits and prevent unwanted transients
from affecting transmitter operation. All
isolated inputs are driven by isolated dc to
dc converter U1 to prevent unwanted
transients from affecting the transmitter’s dc
supplies. The monitor inputs are shifted in
through shift registers U6 and U9. These
values are then relayed to the control/display
PWB over the internal serial bus using
RS485 transceiver U12.
6.5.4.2 Site Control Points
Shift registers U17 and U19, controlled by
microcontroller U13 over the SPI bus will
control relays K1 to K16. Control point logic
levels are determined by the control/display
PWB and are communicated to the NDB site
interface PWB over the internal serial bus.
6.5.5 Modem (Optional)
See Figure SD-3. An optional modem (U11)
can be provided to interface the transmitter’s
RS232 Ext Serial Link to a PTSN. The link
provides remote monitoring and status for the
transmitter.
