Kenwood TR-7400A Service Manual page 7

5.
The TR-7400A incorporates new1 y developed circuit
techniques such as a PLL frequency synthesizer as the local
oscillator.
PLL CIRCUIT
The block diagram is given in Fig. 1.
The circuit is outlined below. The outputs of the VCO
and LOCAL OSC are mixed together and converted to
r------------
DISPLAY UNlT (X54-1210-10)
I
I
2.56 MHz
PD UNlT (X50-1380-10)
Afr and Af,! are the frequency deviations of the REF OSC
and LOCAL OSC respectively. You will see how the VCO
frequency changes with the deviations and N preset in the
programmable counter.
El
1
UNlT (X50-1370-10)
PLL Circuit Block Diagram
Fig. 1
fo
-
DIVIDER
P.
1/Nr
2
Fig. Frequency Relationship of PLL
----
N (fr +Afr)
(41 9.)
+ +Of
=-----
Nr
D.
LOCAL
SYSTEM
-
TX. RX
*MIXER