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OCUBIC
COMMUNICATIONS
SIWAIV
-DIVISIDN
this stage
is equal to Rl's value, 'and the
output impedance is low.
Since both
input
and output impedances can be quite low, the
bandwidth may
be
very wide--IOO MHz or gr-
eater.
.
Since the feedback path oI the circuit
(R2) allows
just
enough
signal
from the
output to
be
fed back to the base to cancel
out
that
coming
in
through
Rl (and the
feedback signal is
out pf
phase
with the
incoming signaI),
little or no signal will
be
seen at the base.
Tt
is
a
"virtual"
ground, so far as voltage is concerned:
This characteristic can be used to sum
two or more signaIs, setting different gain
values for
each signal,
if
desired.
The
gain for each signal is proportional to the
ratio of the feedback resistor (R2) to it's
own
input
resistor only;
the other input
resistors
do not
affect the
gain of that
particular
signal.
Tt is
interesting
to
note that
this is
a summing,
not mixing,
amplifier,
often another
useful
property
of the circuit.
RI
o='
R2IRI
RI-!
~
~ .
~
SUMMING INPUT
A STMPLE TMPULSE NOISE GENERATOR
(fu.e)
Level
~----''''''''-~
Output
82K
Nol.e Generator
lOOK
IM
Speed
On/Off
+
lev
r---.......---........----O~IIt___fII~
(9V.2)
~O.22
The noise blanker circuit used in SWAN radios, like all effective noise
blank ers , is designed to detect
the presence of impulse
noise above a cer-
tain threshold,
and to mute,
or blank,
the output of the receiver for the
duration of that pulse.
(There is
no circuit or scheme
that can eliminate
static or background
hiss types of noise.)
Since operation of the
blanker
circuit depends upon the presence of this
high level impulse type of noise,
1t is difficult
if not impossible to service the circuit unless a cource of
6uch impulses is avail-
a bIe.
Efforts
to ser-
vice it
using the com-
monly
available
test
equipment lineup
are
1neffective,
and
may.
weIl lead to misadjust-
ments--most often, this
section of the receiver
1s never checked
out,
but merely accepted on
faith.
Tt follows,
then,
that a simpIe, inexpen-
siveinstrument
that
generates
this type of
signal
would be
most
useful in
the
service
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