Nautel XR6, Руководство по устранению неисправностей, Страница: 82 / 291

XR6/XR3 Troubleshooting Manual Detailed Circuit Descriptions
Page 2-14 Issue 3.0 2009-07-15
Remote outputs
Remote alarm/status outputs are provided on pins of connectors J2 and J3. A darlington transistor
for each alarm/status output provides a negative logic (current-sink-to-ground) output when a logic
'true' (alarm condition or active status) exists. The switching circuit provides an open collector during
logic 'false' conditions (non-alarm or non-active status condition) and has no influence on the
external monitoring circuit. Each monitoring circuit must present impedance between the switching
device and a positive dc voltage source that results in a current flow of not more than 50 mA. +24 V
is available for use by the remote monitoring circuits on TB1-17.
Audio input
Analog audio input is applied to the
AUDIO
terminals [
+
(TB2-1),
-
(TB2-3) and
SHIELD
(TB2-2)].
The Magnitude component of the IBOC audio input, if used, is applied to RJ45 connector J10 [
MAG
(IN)
] of the remote interface PWB. The Phase component is applied to J14 (
RF PHASE
) of the RF
drive buffer PWB.
The optional DCC inputs are applied to pins of D-sub connector J1. When the DCC option is used,
the analog audio is routed to the DCC PWB via relays K2.
The audio signal is then applied to the balance/unbalance circuit. The state of relay K3C determines
the amplitude modulating source - analog or IBOC program.
Balance/unbalance circuits
The balance/unbalance circuits, which converts the balanced audio input or IBOC magnitude input
to an unbalanced signal, consists of U27A or U28A and its associated components. The output of
differential amplifier U27A or U28A is an unbalanced audio that is a positive voltage for positive half
cycles and a negative voltage for negative half cycles. Any unwanted noise transients that are induced
on the audio input will be in-phase and of equal amplitude. Since the transients are in-phase and of
equal amplitude, they have no influence on U27A's or U28A's output and they will not appear at
U27A's or U28A's output.
Zero crossing detector
The zero crossing detector, for analog audio only, consists of U33C, Q17, CR36, and associated
components. This circuit is the +15 V charge voltage source for C137 during the negative audio half-
cycles. During positive audio half-cycles it is effectively open circuit and has no influence on the
charge state of C137. A small dc bias (0.3 V) is present on U33C's non-inverting input.