Circuit Description - Kenwood TM-2550A Service Manual

CIRCUIT DESECRIPTION
Transmit PLL Loop
The divide ratio is increased by 91 during transmit opera-
tions. This causes the TX VCO frequency to be locked at a
frequency 455kHz higher than the RX VCO frequency
which prevents internal mixing. When an error occurs that
is greater than the correction voltage limits an unlock signal
is generated by !C1. This signal controls the conduction of
Q1 : 2SC2458(Y) which controls Q2 : 2SA1048(Y) to stop
transmissions. Q2 interrupts the bias of the TX driver
stage..
EEEEEEDEERNEAR
N13 -° N11
N44 N2
Fig. 7 MC145151P Block diagram (PLL unit IC1)