ABB Switzerland Ltd 1KHW001489-EN ETL600
d/b/z30
d/b/z28
JR
select R
T202
d/b/z16
d/b/z24
Alarm logic
TX Alarm
WARN
TX RF AL
TXAL
OPTO-AL
TA1
TA3
TA2
T201
TB1
TB3
TB2
+5V
Regulator
+5V
resistors on
heat sink
+12.8V
K201
z8
b6
d/b/z22
z6
TXRF-40W
b8
d6
z2 / b2
RX RF relay
Amplifier 2
TX filter 2
TX filter 1
TX filter 2
OPTO-AL
TXAL
80W to hybrid
relay shown not energized
7.33
26.67
15.67
default jumpers shown
d/b/z32
d/b/z26
HF signal
GND
d/b/z14
GND
z6
GND-CE
d8
d10
plug-out
Fig. 3-21 P3LG block diagram
3.3.11. RF hybrids P3LE, dummy load P3LK
The RF hybrid is used to decouple the receiver from its own
transmitter. Its use is seen where the line attenuation is high,
especially when transmitter and receiver bands are close together.
The transmitter intermodulation products at the receiver input are
correspondingly reduced by the transhybrid attenuation.
As shown by the block diagram Fig. 3-22, the module essentially
consists of a transformer and tuned circuit, which forms a model of the
transmission line impedance. The high ratio of the transformer results
in a low insertion loss between the transmitter and the line model. The
output impedance can be set to either 45 Ohms, 75 Ohms, or
125 Ohms nominal, using jumpers on transformer T1.
Jumpers around the two matching transformers T3, T4 have to be set
according to the bandwidth of the Tx filter.
The RF hybrid also contains the LED to indicate Tx ALARM, the
potentiometer to adjust the receive level and also a coax connector
(RF LINE MONITOR) on the front panel, to measure the Tx signal with
an attenuation of 50 dB (e.g. 100 W output equals 0dBm into a
50 Ohm termination).
3-32 November 2005 Structure and Function
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