Specifications

Chapter 4 4-Wire E&M/TO Configuration
4-9
SETTING TRANSMIT AND RECEIVE GAIN
The transmit (analog-to-digital) and the receive (digital-to-analog) gain for each voice channel can be set
independently using twelve 10-position DIP switches on top of the 4-wire E&M card circuit board. Each
analog channel uses a bank of ten DIP switches, with five for transmit and five for receive. The gain from
each switch is additive, with switches 1-5 providing transmit (analog-to-digital) gain of 1, 2, 4, 8 and 16
dB, respectively. Switches 6-10 set receive (digital-to-analog) gains of 1, 2, 4, 8, and 16 dB, respectively.
With all five switches off, the gain is -21dB. Because the gain from the each switch is additive, any gain
level between -21dB and 10dB is possible.
The digital transmission level is limited by the codec to a maximum of 3.17dBm0. The gain stages may be
set to apply up to 10dB of gain; however, the maximum level of the codec must not be exceeded or
distortion will result.
The analog transmission level may be set to a maximum 9.5dBm before distortion begins to occur.
TRANSMIT (ANALOG-TO-DIGITAL) GAIN
A transformer provides the analog input (T,R) from the 4-wire voice connections to the Access Bank I.
The gain from each switch on the 10-position DIP switch is additive, with switches 1-5 providing gain of
1, 2, 4, 8 and 16 dB, respectively. To calculate the T1 transmit level, use the following formula:
T1 level = Analog Input level + ∑ Gain Switches - 21
The following is an example of setting transmit gain:
Example: Suppose the analog input level is at +3dBm. With all switches off, the
level at the T1 line is +3dBm -21db = -18dBm0. To set a 0dBm0 level
at the T1 line, switches 2 and 5 (gains 2dB, and 16dB) must be turned
on. The level at the T1 line is then:
T1 level = 3dBm + 16dB + 2dB - 21dB = 0dBm0
RECEIVE (DIGITAL-TO-ANALOG) GAIN
To calculate the transmission level on the T1, R1 pair, use the following formula:
T1/R1 level = T1 level + ∑ Gain Switches -21dB
The following is an example of setting receive gain:
Example: Suppose the T1 input level to codec is at -1dBm0. With all switches
off, the output at the T1, R1 pair is -1dBm -21db = -22dBm. To set a
4-wire transmission level of 0dBm, switches 7, 9 and 10 (gains 2dB,
8dB, and 16dB) must be turned on. The level at the T1, R1 pair is
then:
T1/R1 level = -1dBm0 + 2dB + 8dB +16dB -21dB = 0dBm.
E&M VOICE CHANNEL MONITORING
Call Progress LED Indicators
A bank of LEDs on the ABI back plate are used to monitor the status of incoming or outgoing calls on
each of the twelve voice channels. When viewing the LED bank, channel 1 corresponds to the LED in the
top left hand corner. Other channels are arranged left to right, row by row (like reading a book), so