HP 416A - Page 55

NOTE : By us ing a waveguide - to -coaxia l adapter (suc h as a
Hewlett -Packard Model 281A Waveguide to Coaxial
A dap ter), a coaxial slotted line, such as a Mode l 805A
(or B) Slotted Line or Mod el 806B Coaxial Slotted Sec -
ti on , may be used with th e Model 809B ca rriage.
A ratio met er such as the Model 416A Ratio Meter.
A coaxial - to - wavegui d e a dapter ( s u ch as the Model 281 A) to connect
the signal source to the wavegui de .
Descr i ption - Th e following is a general descr ipti on of slotted-line
system connections , operating conditions, an d ca l ibration procedures when
the Model 416A is used as the indicator . Step- by-step operating instructions
are given follow i ng this general descr i ption , under Operating Procedure.
NOTE : When the sequence of instruction s give n in Operating Proce -
du re is followed ex actly, th ere wi ll be little danger of over <•
loading th e ratio meter or the dete ctors,
As indicated in Fig . 16, the tran s m ission sy stem, w hi ch i ncludes a
directional c ou pler a nd s l otted line, is terminated by the load under meas -
urement . The output from the secondary arm of th e directiona l coupler is
connected to a square -l aw detec tor (eit he r crystal or b arre t ter) which, in
turn, is connected to the INCIDENT /REFERENCE input on the Model 416A.
The output of the s lotted - line probe is connected to another square- law de -
tector , and, at the time t he standing -wave ratio is measured , the output of
this detecto r is c onn ected to th e REFLECTED/PROBE i nput on t he Model 416A .
A
mi crowave osc i ll ator is arran ged to deliver t o th e tra nsmission sys -
tem an rf signal modul ated by a 1-kc square-wave voltage. The signal is sam -
pled by the direct i on a l co upl er, and t he 1-kc enve l ope subseq uently is detected
by the detecto r. The detector output voltage is proportio nal to the output from
the signal sour ce, and is used as a reference voltage b y the ratio meter .
Th e calibration p r o cedure involves adj ustments wh ich result, at the
Model 4 16A, in a l ; 1 ratio between th e referenc e voltage and the maximum
standing -wave voltage, F irst the probe in the slotted line is move d along the
line until th e standing -wave max im um point is found. Then the amplit ude of
the volt age picked up b y the prob e is regulated by adj u sti ng probe depth of
penetrat ion . When the indication on the Mo de l 416A meter (upper SWR scale)
is as close to "1 " as adjustment of probe penetration ca n bring it , the ratio
meter SET TO FULL SCALE control (which adjusts the amoun t of gain in the
Model 416A probe channel) is adjusted to bring the meter indicati on exactly
to" 1
11
, which indicates a 1: 1 ratio between the voltage in the Model 416A
reference chann el and the voltage in th e Model 4 1 6A p r obe c hannel.
By th is two - fold procedure ( 1) regulating amplitude by adjusti ng the
proportion of volt a ge c oupled into the probe detector and ( 2) setting the gain
in the Model 416A prob e channel to exactly the a mou nt requi red to bring the
amplitude of the v olt age i n the probe channel to the same level as that in the
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