Tektronix 434, Instruction Manual

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O p e ra tin g In s tru c tio n s —4 3 4
F ig . 2 -5 . ( A ) C R T d is p la y s h o w in g h ig h -fre q u e n c y in te rfe re n c e
w h e n a tt e m p t in g t o v ie w lo w -le v e l, lo w -fr e q u e n c y s ig n a l, (B ) re ­
s u lta n t d is p la y w h e n 5 M H z B W s w itc h is set t o its o u t p o s itio n .
N O T E
I f th e gain o f the tw o channels m u s t be c lo se ly
m a tc h e d (such as fo r A D D m o d e o p e ra tio n ), the
a d ju s tm e n t p ro c e d u re given in the C a lib ra tio n section
s h o u ld be used.
The best m easurem ent accuracy w hen using probes is
pro vid e d if the G A IN a d ju s tm e n t is made w ith the probes
insta lle d . A lso , to p ro vid e th e m o st accurate m easurem ents,
c a lib ra te the ve rtica l gain o f th e 43 4 at the te m p e ra tu re at
w h ic h the m easurem ent is to be made.
Step A tte n u a to r Balance A d ju s tm e n t
T o check th e step a tte n u a to r balance o f e ith e r channel,
set the In p u t C o u p lin g to G N D and the Sweep M O D E
sw itch to A U T O . Change th e V O L T S /D IV sw itch fro m 10
m V to 1 m V . I f th e trace moves v e rtic a lly , ad ju st the fr o n t-
panel STEP A T T B A L a d ju s tm e n t as fo llo w s :
1. W ith th e In p u t C o u p lin g set to G N D and th e V O L T S /
D IV s w itch set to 10 m V , m ove th e trace to the center
h o riz o n ta l line o f the g ra ticu le w ith th e ve rtica l P O S IT IO N
c o n tro l.
2. Set th e V O L T S /D IV sw itch to 1 m V and ad ju st the
STEP A T T B A L a d ju s tm e n t to re tu rn th e trace to th e
center h o riz o n ta l line.
3. Repeat steps 1 and 2 fo r m in im u m trace s h ift as the
V O L T S /D IV sw itch is changed fro m 10 m V to 1 m V .
Signal C onnections
In general, probes o ffe r th e m o s t c o n v e n ie n t means o f
co n n e ctin g a signal to th e in p u t o f th e 4 3 4 . T e k tro n ix
probes are shielded to p re ve n t p ic k u p o f e le c tro s ta tic in te r­
ference. A 10X a tte n u a to r probe o ffe rs a high in p u t
im pedance and allow s th e c irc u it u nder test to p e rfo rm very
close to norm al opera tin g c o n d itio n s . H ow ever, a 10X
probe also attenuates the in p u t signal 10 tim e s. A T e k ­
tr o n ix fie ld e ffe c t tra n s is to r probe o ffe rs th e same high-
in p u t im pedance as the 10X probes. H ow ever, it is
p a rtic u la rly useful since it provides w id e band o p e ra tio n
w h ile presenting no a tte n u a tio n ( I X gain) and a lo w in p u t
capacitance. A standard I X p robe can be used fo r signal
c o n n e c tio n s , alth o u g h it does n o t p ro vid e as high an in p u t
im pedance and m ay re su lt in a lo w e r overall b a n d w id th .
Specialized probes are also available fro m T e k tr o n ix , Inc.
fo r high-voltage m easurem ent, c u rre n t m easurem ent, etc.
See th e T e k tro n ix , Inc. catalog fo r characteristics and
c o m p a tib ility o f probes fo r use w ith th is system.
In h ig h -fre q u e n c y a p p lic a tio n s re q u irin g m a x im u m o ve r­
all b a n d w id th , use coaxial cables te rm in a te d in th e ir
ch a ra c te ris tic impedances at th e 43 4 in p u t connectors.
H igh-level, lo w -fre q u e n c y signals can be connected d ire c tly
to th e 4 3 4 in p u t con n e cto rs using s h o rt unshielded leads.
T his c o u p lin g m e th o d w o rk s best fo r signals b e lo w a b o u t
one k ilo h e rtz and d e fle c tio n fa c to rs above one v o lt/
d iv is io n . When th is c o u p lin g m e th o d is used, establish a
c o m m o n ground betw een th e 4 3 4 and the e q u ip m e n t under
test. A tte m p t to p o s itio n the leads away fro m any source o f
in te rfe re n ce to avoid errors in th e d is p la y . If in te rfe re n ce is
excessive w ith unshielded leads, use a co a xia l cable or a
probe.
Loading E ffe c t o f 4 34
As nearly as possible, sim ulate actual o p e ra tin g c o n d i­
tio n s in th e e q u ip m e n t under te st. O therw ise the e q u ip m e n t
u nder te st m ay n o t p ro d u ce a norm al signal. The 10X
a tte n u a to r and fie ld e ffe c t tra n s is to r probes m e n tio n e d
p re vio u sly o ffe r th e least c irc u it loading. See th e probe
in s tru c tio n m anual fo r loading characteristics o f th e probes.
W hen the signal is coupled d ire c tly to the in p u t o f the
4 3 4 , th e in p u t im pedance is a b o u t one m egohm paralleled
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