Motorola F2265A, Owner'S Manual

Page: 23 / 24

Theory of Operation
3-5
3.3.2.2 C
in
The input capacitor network (C
in
) enables movement
towards the Smith Chart center after crossing the G=1
circle.
C
in
is made up of 26 capacitors (C169-C181, C183,
C185-C191, C196-C198, C201, C202) that can be
switched in and out of the network using relays K120-
K126. C
in
can accept one of 128 values ranging
between 0 pF and 9260 pF.
3.3.2.3 Series Capacitor
The series capacitor (C100, C110) is used either for
handling inductive loads or for overcoming high
frequency parasitic inductances on the line. The series
capacitor can be switched in and out of the network by
relay K100.
3.3.2.4 C
out
The output capacitor C
out
(C101-C106) enables
matching loads whose impedance real component is
above 50
Ω . C
out
can be switched in and out of the
network by relay K113. C
out
is most useful in the low
frequency range.
3.3.2.5 C
med
The function of the variable intermediate capacitor
C
med
(C111 through C117) is identical to that of C
out
.
However, C
med
is not connected directly in parallel to
the antenna and therefore it is more efficient and used
instead of C
out
whenever possible.
C
med
value ranges between 0 pF and 275 pF in 4 steps
under control of two relays (K114, K115). In addition,
C
med
allows tuning inductive loads when the series
capacitor (C100, C110) is not sufficient.
3.3.2.6 Bypass Relay (K112)
The bypass relay (K112) is used to bypass output relays
K101 through K104 when all of these four relays are
closed (inductors L101 through L104 are shorted). This
technique improves transfer efficiency, especially at
high frequencies.
Figure 3-2. RF Matching Network - Block Diagram
3.3.2.7 Relay Activation
A DC power is constantly applied to the relays unless
there are 50ms of DC interrupting during channel
change. The relays are activated by ground potentials,
applied by the Latches and Relay Drivers circuit to the
relay control terminals.
3.3.3 TUNER LOGIC CIRCUIT
Refer to Figure 3-1 for the ATU Block Diagram.
The Tuner Logic circuit controls the operation of the
Automatic Antenna Tuner. It is based on the 68HC11
microprocessor and performs the following functions:
•
Detects channel change and waits for RF tune level
from the radio (based on DC interrupting during
channel changes).
•
Counts the frequency of the RF sample.
•
Processes the sensor data and performs the tuning
algorithm based on this data.
•
Controls the activation of the relay drivers.