HP 416A - Accuracy

Visual Plo t : (Cont ' d)
coefficient versus frequency ov er a range of frequencies maybe
made avai labl e mak es the reflect ometer a va luable, practical
tool in industry, suitab l e for use by non - technical personnel.
Opera ting Procedures - To explain operating procedures when the Model
416A is used in a microwave reflectometer syste m , operating procedures and
considerations , together with a b rief dis cussi on of the major types of errors
which may be encountered, are given b elow .
Oper ating procedu r es fall in to two ge n era l classifications which may be
termed Setup and C a libration. Under Setup is given the proper sequence of opera -
tion for c onnec ting and setti n g into operation the various equipments which com -
prise a reflectometer system. Under Calibrati on is give n the sequence of opera -
tions invo l ved in c a l ib r a ti ng the Model 416A when it is part of a reflectometer
system .
Fo r explan a tory purposes , procedures are made s pe cific to reflectometer
syste m s op erating i n the X and S bands . Pro ce dures given , howe ver, are typical ,
and as t he equipments required for operating in ot her bands become available ,
th e
procedures given belo w maybe applie d in setti ng up an d calibrating reflectom -
eter systems for such other bands.
Typical proc e dures discussed includ e operating techniques for calibrat -
ing at 1 00% reflectio n (b r oa db a nd ), at l e s s than lOOo/oreflection(broadband) , at
100% reflect i on wi th a fixed short (single frequency) • a nd at 1 00 % reflection with a
sliding short (s ingle frequen c y ). Technique for a dju stment wit h a slide screw
tuner an d movable lo a d , to compensate f or di rectivity error 1 , also is included.
Either bar r et te r or cr ys t al d etec to r s m a y be used i n a reflectometer system .
Sequence of oper ati ng p r o ce dure s wh e n c ry s ta l detectors are used is given in the
X band instruction s, a nd p r oc ed ur e to b e followed when b ar retters are used are
gi ven in the S band in s tru ct ion s .
Ac c ura cy
2
- Th ere a re ce r ta i n error s inherent in a re flectometer sys -
tern which should b e r ec og n ize d a nd ta k e n i n to cons i der a tio n . These errors are
referenced in the op e r at i n g i nst r ucti ons , and procedures f or minimizing them
are ind i cated . A b rief a nd g ene r a l d isc u s s i on of th e errors an d t he i r ca uses fol -
lows the opera t ing p r o ce dur es .
NOTE : S in ce a ll e r ror s are not in the same direction a nd are i ndependent ,
th e probab i li ty of errors canceling is large. When minimizing
procedures a r e followed with respect to the remain i ng errors
and mat c hed detectors are used, total error in a swept - frequency
refle c tom e ter system generally can be re duced to below ± 5% ±0 . 01.
In a single-frequency system , error generally can be reduced to
less than ±. 005 for reflection coefficients under 0. 3.
1 See Single - Frequenc y Opera ti on , below .
2
For a det ailed di s cussion of this subject see th e Hewlett - Packard Journal ,
Vol 6, No . 1- 2, S e pt . - Oct ., 1954 .
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