M8SL2-00-002-812 Installation and Configuration D3.17
© Copyright Tait Electronics Limited August 2004. All rights reserved.
5. While in Line-In Level Configuration Mode, the LEDs flash green only briefly
when the dispatch console PTT is pressed
The Line-In level is too low. The T803 is only detecting the high-level guard tone
(HLGT).
While still in Line-In Level Configuration Mode, activate the console PTT and adjust the
Line-In level by pressing the Monitor button (increases the Line-In level) until the LEDs
remain constant green. The top alarm LED will toggle on and off, indicating a level
increase until the top of the range is reached (may be as many as 65 presses). If this still
fails, open up the unit and add JP200, and try again.
6. When the PTT is pressed, a pulsing sound can be heard from the speaker
The Line-In level is too high. The function tones can not be decoded properly hence it
keys off.
While still in Line-In Level Configuration Mode, activate the console PTT and adjust the
Line-In level by pressing the Mode button. The bottom alarm LED will toggle on and
off, indicating a level decrease until the bottom of the range is reached. Using an oscillo-
scope measure the signal on TP204 – the function tone level should be about half the
level of the high level guard tone.
7. The console keys the transmitter correctly except when speech is present
This is known as ‘Talkoff ’ and occurs when the difference between the keytone level
and speech peak level exceeds specification (32dB in 2-wire mode and 35dB in 4-wire
mode), causing the keytone detection to fail.
For reliable operation, the keytone level should be no more than 35dB lower than
peak
speech level.
If it is not possible to adjust the levels at the console, decrease the programmed Line-In
level of the T803 until talkoff is eliminated. This requires that the audio level from T803
to transmitter will also need to be re-adjusted (using the transmitter’s Line Sensitivity
control) to maintain 60% full system deviation for the test tone sent from the console.
Adjust the relative audio levels (keytone and speech) sent from the dispatch console.
8. Keytone Falsing in 2-wire mode
When operating in 2-wire mode with lossy lines (i.e. significant separation required
between T803 Line-In and Line-Out levels) the keytone detector can become de-sensi-
tised by noise.
• Check to ensure that the input level from the receiver is correctly set up at
230mV
rms
(See Section 3.2.4.3).
• Check the receiver mute open level (squelch). If necessary adjust the receiver Gat-
ing Sensitivity control on the front panel of the receiver, so that the receiver mute
opens at a higher SINAD level (12dB or preferably greater). This has the effect of
reducing the noise on the line input of the T803 in 2-wire mode.
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