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v
o l ts .
As
t
h
e
ou tput
swi ngs
d
own
towar d 0,
Q213
turns on
and s
u
pp l ies
c ιι rτent
to t
h
e
front-pa ne l
U
N
LEVE L
E
D
lamp ;
t h en, as the output rises toward
+7
v
o l ts,
Q213
again
tu rns o ff
and
prevents current
flow to
the
UNLE VELED
lamp .
Th is
on/off c
y
c
l
e of Q213
thus
cau ses the
U
NLEVELED lamp to flas h .
W
it h th e inst rume nt's
M
ODULATION
MODE
s
witc h set
to
its
AM p osit ion , mode
sel ect
r
e l ay
Κ201
enabl es
re m ote
sel ection of ei t her CW o r Μ1 modes .
Q212
i
s
an
i
nverter
w
hi ch contro l s
relay
d r ive
r
Q211 .
Wi t h
the
base
o f
Q212
( J 101 p in 30) grounded, Q2 Ι 2
i
s
t
u
rned
of f ;
therefore, Q241
i
s t
u
rned on
an d
e
ff ect i ve ly grounds one si d e of Κ201 's
co il .
Th is en e r gi z es
Κ201 and
ope ns
its con tacts to place t he in st rum ent in
its CW m ode .
Wit h
re l a y
Κ201
in
its de-e nergi z ed
(normally c losed)
p
os i t ion ,
m
od u lat i on
s i gn a l s (D C, 400
Hz,
1
k
H
z,
or EXT .)
from
t h e
Modulation Board are ap
p
l ied
th roug h t h e
r
elay co n tacts to th e
M
ete r
Board
where
t
hey
are
com bined
wi t
h
l
eve l
p rog r amm ing
vo l tage
to produ ce
am
p
l itude
m od ul ation
of
th e
O
u
tput
A mp lif ie r
outp
u
t .
When
K201
is
energ i zed,
its
con tacts
open ;
t hus,
m odu lat i on
s
igna ls a re
r
emov ed from t
h
e
M
eter Boa rd
a
nd inst r
u
m e nt
i
s 1π `he CW
mod e .
RF Le ve l P rogramming
The Programmable
Attenuato r
con tain s
one
10
dB
sectio n
and
four
20
dB
sect io n s ;
h
owever ,
two
of
t
h
e 2 ρ d B
sectio n s are wired together to
provid e
40
dB
o
f
attenuation .
The resu l t ing
f
o ur atte nuator
p
ads
(10 dB, 20 dB , 40
dB , and 20 dB) can be com bined in 10 d B
step s to give atte nuatio n ra nging
from
0 to 90 dB.
The
positi v e ter min a l
o
f
eac h attenuato r section
i
s connecte d to
+27 vol ts
D
C ;
th e n ,
eac h atte n uatoτ
p a d
i s
activated
w
h
e n
required
by
grοιιηιί iτι g its negat
i
ve termina l
t
hr ou gh
one of f o
u
r ide ntica l
inverter/divider
transistor c irc uits .
attenu at io n
wi ll
be
activated as
f o ll ows .
Th e base of Q204
i
s
gr o u nde
d
direct ly .
Th e base of Q206 is g r ounded
through C R205, and t h e base o f
Q208 is
gr o u nde d t
h
r ou gh
C
R 206 .
T
h
is t
u
rns off
inverters
Q204,
Q206,
a n d Q208 whic h
t
urn s
on
dr ivers Q203,
Q205,
and
Q207,
r
es
p
ective ly .
The
dr ive r s
gro u n d t h e
n
egat ive terminals o f
t
h e 20 d B , 40 dB,
a nd 20 d B atte nuator pads th ro
u
g h 8226,
Α 227, and 8228, respectively .
N
ote
th at
CΑ 2 Π5
and
C
R 206
a r e
forward-biased
a n
d
con d u ct
only w h e n
t
h e "8" wir e
i
s gr oun ded .
If t
h
e
"4"
wire
or
"2"
wir e
i
s
g r o unded,
the
diodes a r e r eve r se-b iased and
d o
not
co
n
d
u
ct .
M A I
N
T
EN
A
N
C
E
If α malf unct i o n
occ ur s,
th e
t r o u b l e
can be
l
ocaliz e d and
r
e
p
air ed with
t
h e
a id
o
f
t
h e
c ir c uit
desc r iptio n
and
sc h ematic .
No pr eventative maintenance
i
s required
f
o r
t
he ΑΣ
L
eve l Prog r ammin g
option ;
h
owever ,
p
eriodic
testin g
i
s
r
eco mme nd ed to insure
p
roper operat i on
o f t h e programming
and t h e
P
rotect i on
Cir c
u
its .
Th e
l
e ve l
programming
can be c heck e
d
wit h t h e following procedure :
ΝΟΤΕ
8/1Β - 3
For
examp l e,
to
insert
10
dB
of
Af ter th e
external
RF
s
igna l
i s
attenuation, t
he "1" wire (J 101
p
in 26)
r
emove d ,
I
C201
can
be
unlatched
by
i
s gro u nded b y α contact c l osur e or TTL
m
omenta ril y
r
e
m
oving AC powe r fr om
the
sign a l .
This t urns o ff
i
nverter
Q210
i
n strument .
w
h ic h
t h e n
tur n s on
driver Q209
a n
d
grounds t he
n
egative ter minal ο £
t
h e 10
C
W /λ11
M
ode Se l ection
dB pad thr o ug h
R229 .
If
t
he "8" wir e
(J 101
p in 29) is grounded,
80
dB
o
f
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