Lafayette Petrusse, Руководство пользователя

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Section 4 Maintenance & Adjustment
Circuit Theory ,
The concept of PLL system frequency synthesization is not
of recent development, however, it has not been a long âge
since the digital theory has been coupled w ith the PLL
synthesization; technology. Aithough details of the PLL
theory is-somewhat complicated and riot within the scope
of this brochure, we hereby provide the fundamental
theory of it.
PLL Circuitry. PLL is an abbreviation of the phase-locked
ioop which is fundamentary composed of a closed loop
feedback circuit. The feedback component is the balance of
frequency drifts and the PLL circuit acts to cancel it out.
То detect out the frequency drift of the PLL output, a
fîxed reference oscillator (10 kHz, 1/1024 divided down
from 10.240 MHz) is compared constantly with the input
frequency (10 kH z).'The input frequency is obtained by
dividing the VCO frequency. A functional block diagram
is provided below ander 'PLL Circuit' for the easier under-
standing.
Off-Set frequency oscillator TR-29 The off-set-frequency
oscillator' TR-29 oscillâtes at 14.460 MHz for ail band
Switching bejween these oscillating frequencies is made by
biasing the diodes D 97 to D111.
The off-set frequency signal is obtained at TR-29 emitter
and flows through L-16 and C-88 into TR-25 mixer where
it is beat w ith the VCO signal. The VCO signal is obtained
from the following:
f vco ^ off-set+ Nfr
Where, f Vco = VCO frequency, N - programming code for
divider output, fr =<eference frequency step, 0.01 MHz.
i.e. A t channel #1 in band A, and AM band corresponding
N code is 91.
TRANSMITTER
PLI
CIRCUIT
FM MOO
1C6
MIC
ДМР
IC 9 T R 6 5 /6 6 TR66 TR63
TX M IX E R
1
—
I DRlVERsTH DRIVES 1
— fP O W E R '
_ ,— L.C.6......
J -------- F PW R>
TX
OUT
FL3
X'TAL
-TRS1-
IC3
BALANCE MOD
SSB MOD.
10.6975MHz TR30
Hflh-Г ose
ж
— I
TR30 I
ose H
AM MOD.
f vco = 14.460 +91 X 0.01 = 15.370 MHz
Since the mixer output is determined by two factors-the
off- set frequency output (dependent on band selector
switch) and the VCO output, the mixer output contains
the subtracted frequencies of 0.91. to 3.15 MHz. These
frequencies appear’ in pin # 2 of IC-1 through C-82, and
divided by the progrrammable divider in IC-1 down to 10
KHz which is compared with another 10 K Hz signal ob­
tained from the reference oscillator (10.240 MHz).
The VCO output is mixed with the off-set frequency signal
and applied to the TX mixer IC-9 through band-pass filters
L-43 and 1-44. i.e. At channel 1 in band A, and AM band,
the TX mixer IC-9 accepts 15.370 + 10.695 M Hz = 26.065
MHz is TX frequency. The mised with 10.695 MHz signai
from Tr-30. When receiving channel 1 in band A (26.065
MHz), the Ist RX mixerTR-18accepts 15.370 local signal
at its base, and converts down it to 10.695 MHz IF (for
AM/FM modes, this is the 1 st intermediate frequency).
TR-18 off-sets the 10.695 MHz signal so that TR-30 сап
oscillâtes at 10.6975 MHz for LSB.
PLL
circuit
TR25
MIXER
15.37-17.61 MHz
OUT
T R 2 9
TR26
TR27
OSC I---Ißt— 19Л60М№ 1 VCO I--- [
b
ÜFFER 1
0 .9 l-3 .l5 M H z
1
5 L P F J
PHASE ] SET
BUFFER I------ 1 PROGRAM OIV.|------ H X > - ---------|1 /Ю 2 б C IV |
TR26
I С 5
10
.
26
MHz —Ч0|— I ose
RECEIVER
PLL
C IR C U IT
10.26 MHz
15.37
I
17.61
MHz
ANT
TRl7 TRI8 __
RF AMP h-f MIXER
10.695 TR30
МНг н а м OSC~
XF
p i l - HSSB IF
m
SSB IF H —(PROD DÉrh
TR19
TR20/21 /22 TRlS
ITR8 CF655KHZ TR62/1C8
AM MIX |—|~CF 4 AF POWER
SP
OUT
Cf
FM PET
“Tel
j AM 1F j----1AM DET
[
TR9/10/11 TR23
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