Spectra Engineering MX800 - 3.17.3 VF Delay; Description

MX800 Transceiver Technical Manual
© SPECTRA ENGINEERING 2006 Revision 4.2.3
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delay option is fitted the "Delayed Audio Option" check box is ticked in the
MXTOOLS Configuration screen (Hardware settings tab).
This option is not currently available. Due to ongoing development please refer to www.spectraeng.com.au
for the latest information regarding this option.
3.17.4 Variable & Stepped Tone Encoder
3.17.4.1 Description
Variable tone voting is a method of conveying the received signal strength
information to a central arbiter so that an informed decision can be made as to
which base station will use its received audio.
There are two methods of this type of encoder, Variable tone that works by
superimposing a sliding scale audio tone on the received audio at each site,
and stepped tone that works by superimposing a fixed audio tones per
decision block. This tone frequency being related to the received signal
strength (RSSI). The tone is removed at the central site and the best audio is
turned around for retransmission. This requires a VF connection between
each base station and the central arbiter.
Prior to a tone being superimposed the receiver VF is notch filtered at the
tone frequency.
A Second PTT function designed for mobile voting systems transmits carrier
with no modulation (including no CTCSS) to allow mobiles to vote without
lifting the mute in the mobile.
3.17.4.2 Voting Law
The table below shows the default voting decisions points programmed into
the MX800 T19 / T26 option board. These are the corresponding signal
points where by under control of the microprocessor to generates the
appropriate audio tone.
Level 0 refers to the signal level when the mute opens and is less than Level
1. The option board incorporates a signal noise measurement circuit that
needs to be calibrated for the board to perform optimally.
Table 3-8 Signal decision levels/points and coresponding tones.
RF Signal
Decision Points
Level
(uV)
Frequency
(Hz)
Squelch closed N / A 2710
Level 0 signal > 0 2732
Level 1 signal > 0.6 2792
Level 2 signal > 1.0 2856
Level 3 signal > 2.0 2913
Level 4 signal > 5.0 2973