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p
rop er frequency . Therefore, although
t
here are 14 possible
lock points on line G, t h e only one selected will correspond
to the analog-tu ne
d
frequency of the
W
ide Oscillator . The
unit as
d
escribed so far is capable of phase. locked output at
0, ΛΟ . 80 .
.
.
520 ΜΗτ, The following is an ex pla nation of
locking at I MHz intervals.
To allow
p
hase locking at 1 MHz inte rvals . the refere n ce
freque ncy to mixe r
1
i s made a
d
justa ble in 1 MHz steps
ove r α 40 MHz range ( ΙΛ 48-1487 MHz) .
If, for example, t his reference frequency to mixer 1 were
1449 MHz .
t
h e in p ut ra nge [ο
t
he phase detector would
loo k
t
h e sa me except the entire range would be shifted I
MHz to
t
he right.
L
oc k points
w
oul d
t
hen
b
e possible at
o
utput f r equ encies of Ι , 41, 81 MHz, etc.
B
eing a ble to change t h is
r
efere n ce in 1 MH z steps allows
phase loc king from 0 to 520 MHz in 1 MHz steps.
To
p
rovi d e ph ase locking in 1 kH z steps,
t
h e PLL 4 phase
detector's reference from PLL 1 ίτ a
d
justable in Ι Is ΙΛτ steps
(10.000 to 9.001 MHz), This causes the Wide Oscillator
fre qu ency 2ο
c
hange in 1 kH z steps in ord er to
keep the
loop locked.
PLL 3
The pu rpose of PLL 3 is to stabilize the
N
arrow Oscillator
at α frequency of 1198 MHz.
Fig ur e 3-6 shows α si mp lifie d block d iagram σ ( PLL 3. T h is
loop
o
perates in t h e same manner as PILL I and PILL 2,
exce p t t h at it
d
oes not require the rise of α programm able
co un ter. The 1198 ΜΗ : output from the Narrow Oscillator
is combined in α
m
ixer with α 1200 MHz crystal controlled
signal . This
p
roduces α 2 MHz difference signal,
T
his signal
is fe d to α ph ase detector where it is compared to α 2 MHz
r
eference . Any
d
ifference i n
t
he inp ut signals will
p
ro du ce
an error voltage w hic h is app lied 2 ο
t
h e Narrow Oscillator
(VCO) to correct the fre.clumncy error
PLL 5
PLL 5 supplies the
r
eference for
P
IL L 3. Unlike α stan dard
ph ase-locked loop, the VCO can he modulated- In AM and
C
W, th e VCO is locked on 2 MHz, In the FM mode, the
VCO is mo du late d, bu t the loop ignores mod ulation w hich
is faster [ban 50 Hz ; thu s the cente r froquencv remains
loc k ed .
T
h e loop includes α voltage-controlle d oscillator, α
d
ivider
for reducing the frequency f r o m 2 MHz to Ζ kHz. a phase
d
etector, a nd α filter for the ph ase detector output . If the
variable
i nput to
the ph ase
d
etecto r deviates from
t
he
r
efer ence
f r e qu ency
(slower
than 50
H?), the phase.
detector sands, an error signal in the VCO to correct the
frequency .
C R YSTA L REFERENCE
All the re ference frequ encies for the ph ase-locked loops
in ,
d
eιίνeι1 Γrπιη α single 40 ΜΗτ crystal 5 οιι(εe by Means
of app ropriate multiplication or division .
3.2 .3
SUB ASSE
M
BL Y D ESC R IPTIONS
Τ
h e overall block diag ram discussed in
t
his section describes
b
asica ρ y
h
ow t he i n st ru ment functions as α
u
nit. T he unit
is made up of 12 module assem blies and
t
hree
p
rinted
circuit card asse mb lies . These c αη
b
e i d entified in Figure
5-6 . Sections 3 .3 thru 3.17
d
escribe t he operatio n of
eac h subassembly,
T
he name of t h e su bassembly describes,
to an extent, th e pr imary function it
p
erfo rm s .
3.3
C315- ME TER BOARD
The primary function of this assembly is to provide the
p
rogram voltage to
t
he leveler circuit for t he RF a m plifier.
Ι " also includes t he R F πιιιρυ t level METER whic h αρμrνι rs
dππιι g π (lie instrument front panel (see Figure 3 Α) .
3 .3 .1
LEVEL PR OG RAM
During CW operatio n of the instrument, the level
p
rogram
is controlled
b
y the OUTPU T VERN I ER on the front
panel. T he outpu t of this control goes to two range
calibration circ uits whic h convert
t
he voltage fr o ι n t h e
OUTPU T VERN I ER to α voltage level
a
pp ropriate to drive.
t he leveler ci rcuit in the Output Am plifier mo dule.
T h e "low" ci rcu it
p
rovi des the
p
rogram for all ranges of the
denied
p
ower output
d
ial except +10 dBm. At "+10", the
level
p
rogram is ta ken from the "hig h" circuit .
T
h e "hig h"
level program enables the full gain capabilities a' the
Output Amp lifier to
b
e used whe n
t
he output is not
α mρΙιιυ de mo
d
ulate d,
3.3 .2
M
OD UL ATIO N
T
he modulating signal fro m assem bly C316-2 is applied to
the OU TPU T VERN I ER w h ic h ultimately causes the RF
level to
c
h ange . The leveler in th e Output A mp lifier does
not cause the RF level to respon d linearly to changes n the.
level
p
rogram voltage.
To
compensate fo r
t
his, α stage is
in cluded to
s
h ape t he modulatio n signal before it is applie d
to the OUTPU T VERN I ER .
3.3 .3
ME TER
T
h e front- p anel METER is controlled by the level program
when the ME T ER switc h is set to OU TPUT. The ME TER
an d its dr iver circuits are cali brated to
d
is play α reading
correspo n ding to t h e actual RF level fr om t h e Output
Am plifie r mo du le .
3- ϊ
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