SNV-12 Operations Manual
5-1
5
Features and Capabilities
5.1
General
This section explains the features and capabilities of the SNV-12. See 8.2 for a list of features
supported in various software versions, beginning with revision 2.50. The software or
hardware installed in your SNV-12 may not support some features listed.
5.2
Hot Insertion of Modules
In the SNV-12 system any module (except the PSM-1 Power Supply) in the chassis may be
inserted or removed with power applied without damage. This doesn't mean modules may be
indiscriminately exchanged without temporarily disrupting system operation, so the following
cautions apply: Changing even an idle Site Voter Module may disrupt a currently voted path. It
is best to wait until the entire system is idle before changing a module. Changing a Console
Interface (CIM) or Control Processor (CPM) Module will certainly disrupt the operation
temporarily, and will require the system to be re-initialized (power shut off and back on).
5.3
Serial Port
All voter control functions and complete voter status can be accessed via the SNV-12‟s RS-232
serial port. The serial port connector, located at the rear of the unit, is a DB-9 (female) wired as
a DCE interface. The word is fixed at 8 data bits, one stop bit, and no parity. Baud rates
selectable on the CPM Module are 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, and
57600. CPM module dipswitch SW1 is used to set the baud rate. See Sections 3.11.3 and
3.12.5.1. The serial remote control protocol is listed in Section 6.
5.4
Serial Control via Telnet
The serial remote control protocol is available via the Ethernet interface using the Telnet
protocol. The control protocol used for telnet is identical to the protocol used for the RS-232
serial port described in section 6. Section 6.4 provides details specific to the Telnet port.
5.5
SNR Voting and Noise-Only (FM Mode) Voting
Each Site Voter Module uses a Digital Signal Processor to continuously measure the signal and
noise levels of the audio input from each receiver site. The signal measurement is made in the
300 to 800 Hz band by a Raytheon proprietary speech detection and measurement algorithm.
The SNV-12 measures not only the energy in this range, but also the amount of syllabic
activity. Speech syllables do not consist of continuous energy, but occur at predictable rates
and with predictable harmonic content. Noise is measured in the frequency band above 2200
Hz, again using a spectral approach. The Signal to Noise Ratio (SNR) is calculated from the
amplitude of calculated signal divided by the amplitude of the noise. The SNR measurement
operates from -6 dB to +40 dB. FM systems work best if only the noise measurement is used
for the selection of the best site, while the SNR measurement provides optimal voting
performance in more noisy AM and HF systems.
The SNV-12 DSP algorithms are designed to vote speech and noise signals. For this reason the
unit‟s voting capability can not be verified by injecting test tones into the receive audio inputs.
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