SNV-12 Operations Manual
3-13
3.10
Audio Links
The receive and transmit audio for each SVM must be linked to its associated receiver and/or
transmitter. If the voter is co-located with the console and RF equipment, local wiring can be
used. However, if the voter is separated from the other equipment geographically, other means
of sending audio, COR and PTT must be considered. These include:
Microwave
Radio Links
Leased wireline links
Satellite Links
3.10.1
Microwave Links
Microwave systems provide good audio response between 300-3000 Hz and are typically more
reliable than landline based links when properly designed, installed and maintained. E&M
signaling is also available in some systems. Various microwave systems are used, including
analog, digital, and unlicensed spread-spectrum microwave. Though initial system
infrastructure costs are higher for microwave systems, there are no recurring monthly charges
as opposed to leased line circuits or leased T1s.
3.10.2
Radio Links
Radio links may be used where microwave systems are not cost effective or may not work
correctly. Typically the receiver‟s audio is relayed via a UHF radio link back to the voter site.
At the voter, a UHF receiver passes the audio to the specific SVM. This type of system may be
configured in one of the following ways:
3.10.2.1
Use Of Pilot Tone At The Voted Receiver Site
With this method, the link transmitter is constantly active, transmitting pilot tone to the voter
when the voting receiver is squelched. The link receiver passes the pilot tone and audio to the
voter. No COR signal is required from the link receiver by the voter.
Advantages:
No delay in COR signal reaching the SVM.
Fault detection feature in each SVM will detect the loss of pilot tone, providing an
indication of loss-of-link condition.
Presence of a constant signal on the link frequency reduces the chances of another
potential co-channel user from selecting the frequency and possibly causing co-
channel interference.
Disadvantages:
Link transmitter is constantly keyed.
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