RFL 9780 RFL Electronics Inc.
September 8, 2001 18-10 (973) 334-3100
18.3.2 THEORY OF OPERATION
For this discussion, refer to the schematic diagram in Figure 18-7.
The RFL 9780 Skewed Hybrid Module uses two hybrid transformers to couple signals between a
transmitter, a receiver, and a line tuning unit. It provides impedance matching and signal separation, and
prevents mutual loading and interference. Signals can be accepted from an amplifier with a source
impedance of 50 Ohms with up to 10 Watts of output power.
The transmitted and received signal passes through a hybrid formed from transformers L1 and L2.
These transformers each have two secondaries, interconnected so that the first secondary of one
transformer is in series with the second secondary of the other. One set of interconnected secondaries is
connected to the line tuning unit through edge connector A24/C24 (high) and A25/C25 (low). This
allows both the transmitter and the receiver to be coupled to the line tuning unit. The other set of
secondaries is connected across the internal balancing network formed by resistors R4 through R11.
The coarse balance switch SW1 and fine balance potentiometer R4 can be adjusted to vary the
resistance across the transformer secondaries, which determines the amount of transhybrid loss. If
additional transhybrid loss is required, the internal balancing network can be disabled by placing
jumper J1 in the “B” position and placing an external network across edge connector terminals
A18/C18 and A19/C19.
The transmitter output is connected across the primary of L1, and the receiver input is connected across the
primary of L2. Transmitter output signals are coupled through L1 to the line tuning unit, and incoming
signals detected by the line tuning unit are coupled through L2 to the receiver. Transmitted signals are
attenuated by about 0.3 dB as they pass through the Skewed Hybrid module, and received signals are
attenuated by about 12.5 dB. Because both the received signal and its noise content are attenuated equally,
signal-to-noise ratios are unaffected.
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