Viavi 3900 Series Operation Manual page 173

6. 3. 3. D Co up l in g S o ft Key
Th e Ca p tur e S o ft K ey a cc es se s a S oft K ey su b- m en u t ha t a llow s us er to de fin e
R es olu tio n a nd V id eo B an dw id ths a s w e ll a s S w ee p Tim e .
Th e Co u plin g So ft K e y M e nu c on sis ts of R B W, V B W a nd S w ee p T im e se ttin gs w hic h are
all inte rd ep e nd en t a nd g ov ern th e us efu ln es s o f a tra ce . T he se S of t K ey s a re co n trol led
by in ter -re late d ac tio n s o t ha t c ha ng ing th e va lue o f o ne ch an g es on e or bo th of the
ot he rs to o ptim iz e th e dis p lay a nd p re ve nt a n inv alid se ttin g. R BW, V B W a nd S w ee p T im e
ca n be se t to A U TO o r M A N U AL o pe rat ion .
NOTE
6. 3. 3. E Res B W (Res ol u ti on B an dw i dth ) S oft Ke y
R es olu tio n B a nd w idth s ets th e b a nd wi dth o f th e I F fi lter . R es olu tio n i s th e ab ility of the
C ha nn el An a lyz er t o d isc rim in at e b et we e n s ign a ls c los ely s ep ara te d i n fr eq ue n cy. Fo r
ex am p le , if tw o sig n als ar e a n aly ze d, the C ha n ne l A na lyz er is o n ly a bl e to d isc rim in ate
be tw ee n the m if the re so lut ion b an dw id th se lec ted is na rr ow er th an th e s ep a rati on
be tw ee n the s ign al s. F ilte r s ele ct ion be co m e s m o re crit ica l if th e to ne s a re at dif fere n t
lev el s. N a rro w res ol utio n ba nd w idt h a lso re su lts in low e r n ois e o n the tr ac e.
NOTE
6. 3. 3. F V id BW (V i d eo B and w id th ) S o ft Key
To v iew s ign al s c los e t o t he no ise le ve l, a lo w pa ss filte r (c a lled th e v id eo filte r) i s
int rod u ce d a fte r th e de tec to r. T he V id eo B an dw id th is th e hig h fre qu en cy cu to ff p oin t o f
th e fil ter. Th e vid eo filt er red uc e s h igh fre q ue nc y n o ise on th e de te cte d s ig na l an d
en ab le s lo w le ve l sig na ls to be id en tifie d t ha t w ou ld ot he rw ise b e b ur ied in th e n oi se .
R a di o T e st Ins tru me nt s
F ig. 6 -1 8 C ha nn el An al yze r C o up lin g S o ft K ey M e nu
F or m an y ap plic at ion s, se ttin g a ll th re e p a ram e te rs to A U T O
p ro vid es a us efu l re p res en ta tio n o f th e sig na l to b e e xa m in ed .
H o we ve r, pa ra me te rs ca n b e se t to sp e cific re qu ire m en ts , all ow in g
th e Te st Se t t o s ele ct the o pt im um s ett ing fo r th e oth er tw o
p ar am e ter s a cc or din g to i nte rn al s et up ta ble s.
Wh e n p er for m ing po w er m ea su re m en ts, the R e so lutio n B an dw id th
m u st be se t to a va lu e e qu a l or gr ea ter th an th e b an d wid th of th e
s ign a l be in g m e as ur ed .
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