Kenwood TM-221A Service Manual page 5

At 144MHz (K,M), fvco (RX) has the following
relationship to the various frequency division ratios :
fVCO=(144—10.695) = [(n X 128) + A] X fosc/R
where, fVCO : Frequency output by the VCO
n: 10-bit binary programmable counter setting
A: 7-bit binary programmable counter setting
fosc : 10.24MHz reference oscillator
R : 14-bit binary programmable counter setting
(2048)
If n=208 and A=37, then;
fyco=[(208 X 128) + 37] X 10240/2048
= [26624 + 37] X5
= 133305kHz=133.305MHz
DRIVE (X59-3120-00)
r
8V when PLL is locked
in transmit mode
OV when PLL is unlocked
in transmit mode A
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R63
% > UNLOCK
Low (OV) when PLL is locked
High (5.5V) when PLL is unlocked
TM-221A/E/ES
CIRCUIT DESCRIPTION
® Unlock detector circuit
Whenever the PLL is unlocked, pin 10 of the PLL IC goes
high ("H") (5.5V), turning off Q15 so that Q1 and Q2
in the module unit (drive unit) turn OFF. The result is
that during receive Q17 is OFF, and during transmit
Q4 and Q5 in the module unit are OFF, This halts trans-
mit, preventing unwanted radiation from the antenna.
(See Fig. 6.)
Rto
FROM PLL OUT TO DRIVE TR Q19.
8V when PLL locked in receive mode
OV when PLL unlocked in receive mode
| Ree c79
1.4V when PLL is locked 2 = ;
OV when PLL is unlocked
Qi7 [> To 1st RX mixer
LA DH °
—— ——_I
C69 discharge is delayed when
voltage rises and advanced when
voltage falls.
Fig. 6 PLL unlock detector circuit