Raytheon SNV-12, Инструкция по установке и эксплуатации

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SNV-12 Operations Manual
3-15
If a standard voice grade line is requested, the following will normally result:
Loss at 1000 Hz will be between 5 and 10 dB.
Long term variation 4 dB.
Frequency response referenced to 1000 Hz:
300-3000 Hz: +3 to -12 dB.
500-2500 Hz: +2 to -8 dB.
Noise: 31 dBrnC maximum.
Frequency translation error: 5 Hz.
Normal impedance: 600 ohms.
Maximum allowed signal into the line:
-6dBm to –13 dBm in-band three second average.
Generally, standard voice grade lines are sufficient for voting systems. However the high
frequency roll-off can cause voice quality to suffer. In addition, when a combination of leased
lines and microwave and/or RF links are used, the loss of the high frequency components in the
wireline line link can affect the voting process. Since the voter works by measuring noise
above 2200 Hz, and the leased link will attenuate noise in this spectrum, the leased-line
connected receiver may sometimes be voted even though the signal is actually noisier than
other receivers linked by microwave or RF.
The ideal situation would have all receivers linked
by the same medium back to the voter. If all are leased lines, all lines should be of the same
type and specifications.
If a combination of microwave and leased lines are used, it will be necessary to request tighter
specifications on the leased lines in order to equalize performance.
By adding C-1 conditioning, the frequency response specifications change to:
300 to 2700 Hz: +2 to -6.
1000 to 2400 Hz: +1 to -3 dB.
C-1 conditioning will improve voice quality and improve performance when a mixture of
leased lines and microwave/RF is used. There will still be high roll off above 2700 Hz.
Adding C-2 conditioning will further tighten the frequency response specifications to +2 to -6
dB from 300-3000 Hz. This further improves the spectrum between 2700-3000 Hz. When a
mix of leased lines and microwave are used, C-2 conditioning is the best choice for optimal
performance.
For a voting system using leased lines only, we recommend all lines have C-1 conditioning
added.
Many systems are configured with a main site with a repeater/base station, co-located with the
voter, and a number of remote receivers linked via leased lines. When these leased lines are
standard voice-grade lines, the frequency response of those links will not be as good as the
connection to the local site. This will cause a difference in audio quality (with the local site
sounding better) and it may cause a remote site to vote even if the local site sounds better due
to the attenuation of noise above 2200 Hz (where the voter measures the noise). This is the
same problem that results when microwave and leased lines are used together. Conditioning of
the leased lines will improve performance on such systems.