ZETRON 4000 Series, Installation Manual

Page: 182 / 418

Audio Level Adjustments
182 025-9533Y
Before Adjusting Levels
Before adjusting the levels on the dual channel card, it is important to set the gain settings
in other parts of the S4000 system to the default. First, assure the console microphone
level has already been adjusted to make up for any audio level loss between the console
and the back room equipment. When this adjustment has been completed the front panel
“MIC” test point on the console interface card will read -10 dBm (0.245 V rms = 0.69
Vpp) when the console is transmitting a single frequency alert tone, and the console LCD
meter should be reading “0 dB” during alert tone transmit. Next set the software gain for
the channel to be adjusted to the default “51” (00 to 99), this effects the level of the
console logger output port and the console LCD meter reading when audio is being
received.
Setting Rx Levels for Dual Channel Cards
Adjust the receive audio calibration level at the DCC to the minimum expected audio
signal level. This should be the level of the audio output from the radio when receiving a 1
kHz sine wave signal at 40% radio channel deviation. The maximum signal level is 30 dB
above this adjustment level and the “CALL” indication level is 28 dB (the default
threshold) below this adjustment level. The CALL level is programmable from 14 dB to
28 dB below the AGC knee of compression. A typical sine wave receive calibration level
(from the radio) is - 15 dBm (390 mVpp).
Systems with a high ambient noise level should be calibrated at a higher signal level
(approximately -8 dBm or 870 mVpp) to provide minimum gain of the background noise.
The disadvantage of calibrating at the higher signal level is that for calls coming in
significantly below the calibration level, the dispatcher may need to turn up the volume.
Figure 36 shows the audio levels.
Figure 36: Receive Audio Levels
Audio
Levels
Maximum Input
Calibration Level
(-15dBm typical)
Call Indication
(programmable)
30 dB
28 dB