HP 416A - Page 43

5, (Cgnt'd)
of even minimum level will cause the eye to give a definite indication :
the shutte r will move toward closure. As the volt age of an input sign al
of proper frequency approaches the maximum level, the eye closes
completely. If the eye overlaps by more than I /32
11
, indication is given
that the frequency of the voltage is correct but that the level is foo high.
a. To adjust the modulation frequency on the i n put signal:
(I) If there is an external attenuator in the line , set it at approxi-
mately 5 DB. (The setting of the Model 6 70SM is at ·) , ) If
there is no external attenuator in the line, change the setting
of the ATTENUATION control on the Model 670SM from 5 to
approximately 4.
(2} If the tuning eye does not indicate by moving its shutter toward
closure, SLOWLY adjust the MOD. FREQ. control on th e M odel
717 A until the tuning eye shutter peaks . S tarting fr om th e ex· -
treme clockwise position of MOD. FREQ., slowly turn the con-
trol counterclockwise until a tuning eye indication is obtained.
(If the eye shutter does not mo ve, return MOD. FREQ. to its
extreme clockwise position, s et t he ATTENUATION control on
the Model 670HM at 3, and readjust the MOD . FREQ. control
on the Model 71 7 A until a t u ning e ye in dication is o btained. )
CAUTION : Care should be taken to make c e rtain th at the correct
modulation frequency is chosen and not some sub-
harmon ic of 1, 000 cycles. For a 1, 000- cycle out-
put , the MOD . F R EQ. control knob s e tt i ng will be
almost completely clockwise.
b. If the tuning eye ove r lap s by m ore t han 1 /32
11
,
reduce th e leve l oJ
the input signal.
(1) If there is an external atte n uator inthe l in e, increase the setting
of t he attenuator, as requ ir e d, to br i ng t he tuning eye overlap
to 1 /32
11
or less . Lea ve the s et ting of the Model 670SM ATTENUA-
T I ON control at O.
(2) If there is no external at te nua t or, r e duc e the level of t h e output
sign.a l at the Model 670SM by adjusting the setting of the AT-
TENUAT I ON control.
Calibration ( 100% R eflecti on , Broadband) (S Band )
1. On the Mode l 670SM oscillator :
a. Set the limit stops on the FREQUENCY - KM C d ial for desired rang e .
For the S - band system being described , set one limit stop at 2. 6 km c
and the other at 3. 95 kmc.
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