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AE/LZB 119 1890 R1A
The 450 KHz signal is filtered in a ceramic channel
filter and put into the amplifier in the IC which amplifies the
signal 44 dB. Another filter is used to complete the channel
and noise filtering process before the signal is limited (58
CIB gain). Each filter (Z204, Z206) is a 4-pole bandpass
filter with a center frequency of 450 KHz and a 3 dB
bandwidth of +/- 15.0 KHz. The limited 450 KHz signal is
fed to the digital discriminator in Bertram, amplified, and
de-emphasized before being passed to Lina for finther audio
processing.
RSSI
A current proportional to the logarithm of the RF input
power of the received signal is produced in the IF/AF chip.
An internal impedance converts the current to a voltage
which is buffered by an internal operational amplifier in
N201. R210 and R211 control the gain of this buffer while
C221 and R210 form a single pole low pass filter to
attenuate the high frequency noise on the RSSI line above
16 KHz.
RSSI Range
The slope of the RSSI voltage is affected by the RF/IF
gain present in the receiver as well as the gain of the RSSI
buffer. The slope of the RSSI curve is nominally 30 mVIdB
and covers the range from no signal input up to about -56
dBm. The useable range is approximately 70 dB. The RSSI
output voltage ranges from approximately 1.2 YDC at no
signal input to approximately 3.5 VDC at maximum. The
lower end is controlled primarily by the IF/AF gain of the
receiver while the upper end of the RSSI voltage is
controlled by the supply voltage of the internal RSSI buffer
inside N201. N201 operates from a nominal 3.7 VDC
supply. The AID converter in Bertram that reads the RSSI
voltage operates from a 4.8 VDC supply.
CONTROLS AND INDICATORS
The 18-button keypad, the internal speaker and liquid
crystal display (LCD) are all located on the front of the
radio.
Viewed from the front the lower microphone is
located in the lower left corner, the upper microphone is
located in the upper left corner and the earpiece is located
above the display. The antenna is located on top of the
radio on the left side.
10
Display
Figure 2 - Display
The Alphanumeric Field is on the top line of the
display. The Alphanumeric Field displays:
•
Names and memory locations, etc.
•
Messages, queries, and warnings.
•
"Air Time" at end of a call.
•
Battery level indicator.
The Numeric Field is on the second line of the display.
The Numeric Field displays the telephone number entered
on the keypad, or recalled from memory.
The Status Indicators are on the bottom line of the
display.
The following is a description of each status
indicator
EMG
Emergency. Indicates that an emergency is
declared on the current group.
SERV
Service. Indicates control channel.
TX
Transmit. Indicates unit is transmitting.
SCN
Scan. Indicates Group has been added to
Group Scan List. Flashing indicates scan
function is turned on.
BSY
Busy. Unit is active in some type of call.
Shown during a call and also while an
outgoing call is being connected.
Who Has Called. Flashes to indicate that
WHC
you received an individual Call.
Battery. Flashes when battery reaches level
B0.
BUTTON
PUSH-TO-
Located on side. Enables radio's transmitter.
TALK
PTT must be held down to transmit during
(PTT
simplex operation.
button)
MONITOR
Located on side. Same function as
keypad except it will not turn scan on/off.
C
key on
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