Raytheon SNV-12, Инструкция по установке и эксплуатации

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SNV-12 Operations Manual
5-6
It‟s possible to reduce the sensitivity of the pilot tone detectors by approximately 7 dB. This
may assist operation in environments where local environmental noise such as sirens (or added
noise, such as alternator whine) at the same frequency as the pilot tone sometimes causes
falsing of the pilot tone detector. Falsing means that the RX audio at the pilot tone frequency
causes the SVM to incorrectly determine (usually momentarily) that an SVM is squelched. The
pilot tone detector is acting properly based on the frequency content of the RX audio. Reduced
sensitivity reduces the falsing without negatively affecting operation as long as the pilot tone is
generated at a high level (preferably at the same level as voice audio).
Note: A PTG-10 pilot tone generator can be ordered from Raytheon and
installed at a remote site for receivers without pilot tone capability. Its
inputs are receiver audio and COR. Its output is two-wire balanced audio
that has a pilot tone (when COR the signal is inactive, indicating that the
receiver is squelched) or receive audio (when COR is active). The PTG-
10 allows the connection of remote receivers to the SNV-12 using only a
single pair of wires. See Section 7 for more information regarding the
PTG-10. See Table 1-3, Optional Equipment, for ordering information.
5.10.2 Receiver with Hardwired COR Signal
Most FM receivers provide a COR output signal, and if the receiver is installed in close
proximity with the voter chassis or linked via microwave this signal can be wired to Pin 13 of
the associated SVM terminal block. This signal is expected to be active low (a logic level
below 2.5V or a short to ground indicates COR, or signal received). A dipswitch on each SVM
module accommodates receivers with active high COR outputs. Again, see Section 3.12.6.3.
The SVM-2 Hardwired COR input may be configured by an internal jumper to accept an E&M
level COR input. Please refer to Section 0 for E&M interface drawings.
5.10.3 Unsquelched Receiver
When this COR type is selected, the SVM assumes that there is a valid signal present at all
times. Its Unsquelched LED will always be lit. If all SVMs use this COR type, all SVM
Unsquelched LEDs are lit at all times, and the SNV-12 votes one of these sites based on the
best signal quality measured among all sites, even when no receivers are unsquelched. Other
SVMs in the system may be set for other COR types, and will be eligible for voting (UNSQ
LED on) only if they detect a valid signal based on their COR type (for example, the absence of
pilot tone for Pilot Tone COR sites, etc.). The SNV-12 will always select the voted audio
signal based on the signal qualities of all eligible sites (UNSQ LED on). In FM Mode the voter
selects based on noise only and could vote an Unsquelched COR site with no signal over a
different type of COR with a real signal. The Unsquelched Receiver COR option is definitely
not recommended for FM systems; it is more suited to AM or HF SSB use. If a COR signal is
available from the receiver, either Hardwired COR or pilot tone generators should be used.
The Line Fault Detection feature is not operative for SVMs that use this Unsquelch COR type
(see Section 5.11). The Holdover Timer feature will also not function if any sites use this COR
type because the Unsquelched Receiver COR sites are always unsquelched and the Holdover
Timer starts when all sites become squelched. See Section 5.17.