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c. Coaxial Relays and Attenuators.
the setting of six-step signal atten-
(1) Coaxial relay K702. With this relay
uator AT702. The division of atten-
in its energized condition, the out-
u a t i o n between the rf and the if.
signal paths maintains an optimum
put of the impulse generator is
coupled through a set of relay
s i g n a l - t o - n o i s e ratio.
c o n t a c t s to 20-db fixed attenuator
d. Typical Tuning Unit. The attenuated
signal is coupled from six-step signal
(2) F i x e d a t t e n u a t o r A T 7 0 1 , 2 0 - d b .
attenuator AT702 to the-input of the tuning
u n i t in use, through multipin connector
T h i s fixed attenuator, coaxial in
structure,  attenuates the signal
J701 (on the main unit) and its mating plug
from the impulse generator by 20-
(on the rear of each tuning unit). The tyical
d b and couples the signal to de-
tuning unit shown is representative of
energized coaxial relay K701. With
tuning units 1 through 4; however, circuit
t h i s 20-db fixed attenuator in the
v a r i a t i o n s exist in each because of the
c a l i b r a t i n g signal path, the output
d i f f e r e n t frequency ranges encountered.
of tie impulse generator agrees
(1) R f section. In the tuned rf ampli-
with the engraved numerals on the
f i e r , the signal is amplified and
front-panel coarse and fine impulse
c o u p l e d to the mixer stage, which
g e n e r a t o r controls.
also receives a signal from the
(3) Coaxial relay K701. With this re-
local oscillator. Sum and difference
f r e q u e n c i e s are produced in the
l a y in its deenergized condition,
the output of 20-db fixed attenuator
mixer stage, but only the difference
AT701 is coupled through one set
f r e q u e n c y is accepted by the if.
of relay contacts to six-step signal
a t t e n u a t o r AT702.
(2) I f . step attenuator. The output of
(4) Six-step signal attenuator AT702.
t h e mixer stage is coupled to a
This cartridge-type attenuator has
three-step if. attenuator, which
a flat response to the complete fre-
operates with rotation of the signal
quency range of the test set, from
attenuator control (c(4) above).
1 5 0 kc to 1,000 mc. Six steps of
(3) If. amplifier. The difference fre-
attenuation are provided by the use
quency from the mixer stage is
o f coaxial networks, which result
amplified by a conventional trans-
in a low-voltage standing wave
f o r m e r - c o u p l e d if. amplifier. The
ratio (swr) at any input frequency.
output signal is applied to the sealed
E a c h attenuator section is a re-
detector-electrometer  assembly.
(4) D e t e c t o r and electrometer as-
s i s t i v e T-pad, in which the series
elements are rod resistors, and the
s e m b l y . This assembly is identical
s h u n t element is a disk-type re-
a n d is interchangeable in all four
sistor. The geometry of the innter
tuning units. Two detectors are in-
and outer conductors of each atten-
c l u d e d within the assembly. One
u a t o r section produces a 50-ohm
detector provides drive for the
line impedance at the input and out-
a u d i o amplifier in the main unit  e
put of each network. Two settings
The other detector provides drive,
o f the six-step signal attenuator
t h r o u g h  high-impedance  electro-
control provide zero attenuation of
m e t e r stages, for the vacuum-type
the calibrating signal. The four re-
v o l t m e t e r indicating circuit in the
maining settings provide 10-, 20-,
main unit.
40-, or 60-db loss in the rf signal
e. Indication Circuits.  Two indicating
path; additional attenuation of 10 or
c i r c u i t s are provided in the main unit.
20-db is inserted into the if. signal
(1) A u r a l . The aural indication is de-
r i v e d from electrometer assembly
path (fig. 2). This loss is introduced
by operation of relays in the if. step
audio detector V1. Its output signal
attenuator, which are controlled by
i s coupled through terminal A1 of

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