Raytheon SNV-12, Инструкция по установке и эксплуатации

Страница: 147 / 206

SNV-12 Operations Manual
5-5
5.8 Voting Lock (COR Lock)
The prevention of voting transitions in mid-sentence is sometimes desirable. Therefore the
SNV-12 provides an optional mode of operation in which the SVM Modules make an initial
audio quality decision. The vote occurs, and the SNV-12 locks onto that voted site until the
voice transmission is complete and the voted site becomes squelched, at which time the SNV-
12 is free to vote again. See Section 2.9.3.3.
CPM SW4 can be used to set the amount of time that SNV-12 will wait, following the initial
detection of an unsquelched SVM, before the Voting Lock is put into place. See 3.12.5.4.
5.9 Data Detect & Lock
During the voting of speech signals, voting transitions in mid-syllable will not significantly
harm the intelligibility of speech. However, transitions from one receiver site to another in the
middle of a data stream may cause bit errors and possible resynchronization problems. The
CPM module switch SW3-4 commands the voter to lock onto the voted site when data is
detected, and remain locked until the voted site is squelched. See Section 2.9.3.3. The line fault
timer is disabled when an SVM module is locked on data. The present standard data is defined
as 1400 Hz radio telemetry data;
this data detect & lock mode was removed from all software
revisions above 3.38 in the SVM-1 module, to make room for more commonly requested
features
. All versions of software with SVM-2 modules support this feature. All Data
Detection algorithms and software are special order options to the SNV-12.
5.10 COR Types Accommodated
Each Site Voter Module is only eligible for voting only when it determines that its associated
voting receiver is sending a valid signal. This determination can be based on an active COR
(unsquelched) input from the receiver (pilot tone or hardwired COR line) or deduced by DSP
signal measurement. The COR types can be set on a module-by module basis by dipswitches on
each SVM. See Section 3.12.6.3. Each SVM can accommodate the following COR options:

Pilot tones (also called “line-proving” tones).

Hardwired COR input signal.

Unsquelched receivers; COR always active. (Not recommended for FM systems.)

Squelched receivers; Audio Level COR. (Not recommended for FM systems.)
5.10.1 Receiver with Pilot Tone
Most LMR voting systems transfer the remote receiver's COR signal to the voter using a pilot
tone which is inserted on the receive audio lines whenever the receiver is squelched, and
removed whenever the receiver is unsquelched. When the Site Voter Module detects the
absence of the pilot tone, it knows its associated receiver is unsquelched and receiving a
transmission. The Site Voter Module supports pilot tone frequencies of 1950 Hz and 2175 Hz.
The DSP software positions a notch filter at the selected frequency so that the pilot tone is not
heard in the received audio. This also ensures that when voted audio is repeated, the pilot tones
are not retransmitted. The tone detect tolerance is +/-30 Hz with notch filter depth better than
40 dB. The selections of pilot tone frequency and Pilot Tone COR type are made by
dipswitches on each SVM. See Section 3.12.6.3.