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3 .10 M29-2-FM REFERENCE
T
h e Μ 29-2 is α voltage . to frequency converter, t he output
of whic h is used ατ α Ιι hαsε lork reference in
the M33-2 .
Th e modu le includes α voltage varia ble cu rrent source
w
hich feeds Idetermines the frequency of) α square wave
oscillator (see F igure 3-15) . Zero volts in yields 2 MHz out.
Th e M29-2 is the VCO for PILL 5. The input to the M29-2
from t h e ph ase detector is essentially added to t he modu-
lation input. Th e FREQ UENCY VERN I ER voltage is also
added here . (T he FREQUENCY V ERN I E R input
b
eco m es
zero volts when the VςΟ is locked)-
3.10 .1
C URRENT SO UR CES
This circuit provides both α
p
ositive and α negative sou rce
of cu rren t. T he
p
ositive sou rce is refe renced to th e
n
egative
source so that the instantaneous currents
in
b
oth sources
are equal .
T
he change in output c urrent is
d
irectly proportional to
the change in input voltage to t he ci rcuit . The input voltage
m
ay va ry
b
etween -5 and 45 volts . The ci rcuit isdesigned
fo r α ve ry linear graph π1
c
urrent out vs. voltage in .
3 .10.2
OSCILLATOR
Th e
s
quare wave output is
p
ro du ce d by t he co mbination
of an integrator and α
h
ysteresis switch . The inlegratco
εοηνerττ α
s
qua re wave to α
t
ria ngle wave . The triangle
wave ca uses the
h
ysteresis switch to produce the squ are
wave whic h is fed
b
ac k to the i ntegrator,
T
he i ntegrator is ma de up of α cu rre nt switch and α
ca pacitor, The square
w
ave app lied to the current switch
ca uses α
s
qua re cur rent sig nal to
b
e app lied to the capacitor .
P ositive co n stant current produces an increasi ng voltage
r
a mp an the ca pacitor and
n
egative co nstant cu rrent
pr oduces α decreasing voltage ram p. For α square
wave
inpu t, therefore, the output is α tria ngle wave . .
Changing the
m
agnit ude of t h e "cu rrents",
b
y changi ng
t
h e input voltage to t h e
m
odule, changes the
r
ate at which
th e capacitor charges and discharges to t h e
h
yste resis
p
oints, thus changi ng the freque ncy of oscillatio n.
3.11 Μ30 .1 -C R YSTA L REFERENC E
This modu le supplies reference fre qu encies α [ 1 kH z, 2 kH z,
1 MHz, 10 MHz, 40
MHz
and its
h
arm onics. 1200
MHz
(from α
120 MHz comb), and 1440 MHz to the ph ase-
locked loops in the instrument Th ese signals are μιοdυε eά
b
y α 40 MHz crystal oscillator and α series of
d
ividers and
mu ltipliers {see
F
igur e
3-14
3 .11 .1
30 MHi OSCILLATOR
This crystal oscillator is the
h
eart ο1
t
he accu r acy ο1 the
Γ re μιιrιι cγ determining ci rcuits in
t
he ίπτι rυιηeιι t- It ιτ
temperature
compensate d
for
freque ncy
sta bility.
Α
varactor diode is in clud ed to
e
n able this oscillator to be
phase
locked
to
α
h
igh stability reference. Α leveler circuit
causes t he oscillator output level to
b
e
t
he sa m e i n all
Μ30-1 mo dules,
3,11 ,2
DI V ID ER S
The fr equencies
b
elow 40 MHz are produced by α se ries
of ΤΤ L co u nters. Α "divide
b
y 4" produces the 10 MHz
output for t h e phase-lock ed loop in Optio n 6 or 5A . This
freque ncy is
f
urther divi ded as shown in F ig ure 3 .16 to
pr ovid e the 1 MHz, 2 kH z, and I kHz outputs.
3.11 .3
MULTI PL I ER S
T
he 40 MHz CW is fe d to α
h
annonie ge nerator
w
hic h
p
rodu ces I
h
e "comb" output .
From the 40 MHz comb, 120
MHz
is selected and applied
to another harmonic generator . Α sa mple of the 120 MHz
εοιιιb output is also fed to α filter w h ic h presides the
1440 MH z output
3 .12 Μ31 Α - kHz STEPS
T
he input to this modu le is the BCD data from t h e fr ο nt-
μαπeΙ "kHz" switches (to the
r
ig ht of t he
d
ecimal ροίπτ1.
Tfw πυτρυτ frequency is (10 MH z -
S
k kH z ), where
S
k ίτ
ι h e ηυιη ber i nd icated by
t
he kH z switches . If t he frequency
is τρι to 428-333 MHz, for exam ple, the Μ31 Α output is
9.667 MHz. The block
d
iagram of the Μ31 Α is s h own in
F igu re 3-17 .
3 .12.1
V
CO
T
he output fr eq uency is ge nerated by α voltage- εοητιοΙΙαι 1
οκίΙΙαιπι which is tun eable from 9 .001 to 10.000 MHz .
3 122
PHASE-LOCKED
L
OO P
I
n cluding the VCO in α
p
hase-locked loop
p
ermits accurate
programmability
.
T
he VCO tuning voltage comes fr om the
p
hese!fηcρυeηεΥ detecto r circ uit . Α 1 kH z sign al from the
Crystal
R
eference is applied to one input of the phase
d
etector ( Ιε9) . Α sample of t h e V CO o utpu t is divi ded by
the programm able divi der, an d
t
h e
r
es ult is app lie d to the
ot h er i npu t of
t
he phase detector . Any
d
ifference in ph ase
or frequency in
t
he signals applied to the ph ase
d
etector
inputs produces an error voltage at the ph ase
d
etector
output, whic h cont rols the VCO . The system is stable only
when the phase an d frequency error is zero, so that the
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