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Servi ce
M
odel 435 Β
S
ERV
IC
E
S
HEE
T 1
viding an ex cep ti o nally stable o utput
l
evel . Th e
calibr ated ou t put
i
s 1
m
W
±0.70% ο at 50 ±5 MHz .
PR
I
N
CI
PLE
S O
F
O
PER
ATIO
N
General
P
ower Su pp ly
Th e
P
ower Meter and α co mp atible po w e r se nsor
Th e
P
ow er
S
upply i s α 24 V series regulator w ith α
a
re
u
sed to measure RF po wer le vels .
F
o r e xa mple,
shun t regulato r co upl ed ac ross the ou tput . The
the power range of
t
he HP
M
odel 8481 Α
i
s from -35
shun t reg ulato r pl aces ground potenti al mid way
to +20 dBm (- - -0 .3 ιι
W
to 100
m
W
)
in to 5051 ; the
between
t
he 24 V p otenti al differ ence t hus provid
frequency range
i
s from 10 MHz to 18 G Hz.
ing supply outputs o f +12 and -12 Vdc. Th e battery
c harging and test c ir cuits a r e automati ca lly
o
per-
P
ower Sensor
ativ e w ith the batte ry insta lled.
The power sensing device di ss ipates the inpu t RF
energy into 50 ohms and produces α do
v
o ltage
T
R
O
UBLE
S
H
OOTI
N
G
proportional to the power leve l. Thi s do
v
o ltage
i
s
sampled creating an ac sign al whi c h is coupl ed to
General
t
he
I
nput Amplifi er for amplifi cat i o n.
Be for e beginnin g to troubles hoot t he
P
ower M ete r,
rem ove t he co ve r fro m
t
h e righ t s ide of
t
he in stru
AC Amplifiers/Range Switch
men t a nd m eas ure t he power s upply vo ltages at
ΤΡ9 and I .F .M.
The ac signal is a mplifi e d by
t
he power sen sor's
Input Amplifi e r and
t
h e
P
ower Meter's Fir st,
Second and Third Amplifi e r s . Th e RAN GE s witch
attenuato rs, which a r e place d b et ween
t
he First
and Second and Second a nd Third amplifi e rs, ar e
u
sed to set the
r
a nge-to- range ga in
o
f
t
he
P
ower
Meter amplifi e r s.
DC Circuits
The Synchronous
D
etecto r co nverts the ac s ign al
back to dc. The output
i
s coupled to th e
D
C Ampli-
fie r via α
L
ow Pass Filter n etwork. The
D
C Ampli-
fier drives the meter, the Servo Amplifier and pos-
sibly an e x te rn a l device t hrough
t
h e RECORDER
OUTPUT jac k.
Servo Amplifier/Auto Zero
α.
PO
WER ME
T
ER AN
D S
EN
SO
R.
Set t h e
The Se rvo Amplifie r amplifies th e
D
C Amplifier
Pow e r Meter's RAN G E switch to t he 1 m W pos i-
o utput. When
t
he fro nt pane l ZERO sw itch is
tion , C AL FACT O R s witc h to 100% ο and
t
he
r
ea r
pressed, the Servo Amplifi er output
i
s connected to
pa nel PO WER REF s witc h to (ON) . Connect the
the Auto Zero circuits completing the auto matic
po wer se nsor to the
P
ower M ete r's
P
O WER REF
zeroing
f
eedback loop. The Auto Ze ro do out pu t
O U TPUT
j
ack .
v
oltage (error signal)
i
s add ed to th e ambien t
temperature output of
t
he power sensor 's po wer
b .
POWER
ME
T
ER AN
D HP
M
OD
EL
11683 Α
sensing device. The pola ri ty
o
f
t
he error signal
R
A
N
G
E
CA
L
I
BR
ATO
R
. Set t he
P
ower Mete r's
and
t
he
f
eedback loop gain force the
D
C Amplifi er
RAN G E s witch to t he 1
m
W
positi o n and C AL
output to ground pote ntial after five seconds.
FA CTOR switch to 100%. Set the
R
an ge Ca li-
When
t
he ZERO switch i s
r
elease d, the Auto Zero
brato r's RANG E s witch to 1
m
W,
P
O LARITY
circuits
h
old
t
he error sig nal con sta nt.
swi tch to
N
ORMAL and FUNC TIO N s wi tc h to
STANDBY. Conn ect t h e
R
an ge Calibrato r to t he
P
ower Reference Assembly
P
ower Meter with
t
he power sensor cable. Set t he
The Α3
P
ower Reference
A
ssembly contains α 50
R
a n ge Ca libr ate FUN C TI O N s witc h to
MHz oscill ator with an ALC loop capable o f pro-
C ALIBRATE .
8-8
Wh en α malfunct i o nin g comp o ne nt
i
s
i
sol ate d to
an assembly or stage, re fer to t he appropri ate Ser-
vice Sh eet
f
or comp on e nt
l
evel
t
roubl eshootin g.
Bloc
k
Diagram Troubles
h
ooting Conditions
The wa v eform s a nd v o ltages show n are norm al
w hen ope r at in g under
t
h e
f
oll owing co ndi t ions .
ΝΟΤΕ
To ex hibi t the co rr ect wa v eform s in
t
he
R
ANG E pos it io ns s how n, t he powe r
se nso r (as pa r t of t h e measurem ent sys-
te m) must m eas ur e power
f
r om -35 to
+20 dBm (50 11) .
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