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panel
controls
the
amount of
undesired
signal
injec-
tion.
This adjustment directly
affects the
modulation
level
of
the
transmitted
signal; therefore
in normal
operation
CODE SYNTH
LVL
must
be in
the
MIN
position. This
summed signal
also goes to the line
drivers enabling
predistorted
waveforms to
be sent
at
baseband
frequencies.
22-4 DECODER SECTION
22.4.1 INPUTS
The
Secure Com
decoder
can
input
encrypted
sig-
nals
in RF
or
baseband form. Modulated RF
signals
can
be
input
through the
antenna port
and
the
RF
II
0
port.
Encrypted baseband
signals
can
be
input in
balanced -line
form at
the LINE I
N
port
on
the inter-
face
junction
box,
or
in single-ended
form by
ground-
ing
one of the
LINE
IN
terminals.
22.4.2
DECRYPTION TYPES
Refer
to paragraph
22.3.2
in
t
he Encoder section
description.
22.4.3
OUTPUTS
The decoder section bas
two
outputs.
The DEMOD
OUT
connector on the front
panel bas the
demodu-
lated signal
(still encrypted) from
the
receiver.
The
other
output
is
available
on
the junction box at
the
PLAIN TEXT OUT
port.
This
output
is the
received,
decoded,
digital data
before
it
is
converted
t
o
an
ana-
log
waveform.
There
is
no
mei\Ils
by which
the
received
audio
waveform
can
be
output by the
Secure
Com
option.
It can be
observed on the Secure Com
internal
oscilloscope
and
heard
in
the
speaker.
22.5
PROGRAMMER SECTION
The programmer section
of
the Secure Com option
performs
three
tasks:
it
outputs programming
data
to
a
radio
to
allow
programming of
a
test
key;
it
sends
programming
data
to t
he
encryption
circuits internal
to
the Secure
Com
option
to
allow them to
be
pro-
grammed with
a test
key; and
it
permits programming
data to
flow
from an external
code
key insertion
device
to
the
internal
encryption
circuits.
22.6.
MEASUREMENTS
22.6.1 BIT ERROR RATE TEST
(BER)
The Secure
Com
option fo
r
the
R2001D
has the
ability
to
perfor
m
various
BER
tests on encrypted
radios,
and on
any
baseband
system
which performs
the audio
encryption
process
as described in para-
22-2
graphs
22.3.1
and
22.3.2.
The
bit error rate test
is
accomplished
by comparing
the plain
text
into
the
encoder circuitry with the plain
text out of
the decoder
circuitry
of
the
R2004/5D
decoder
section or of t he
radio
under
test.
When performing
the
BER
test, t he
R2004/5D
causes the input
to
t
he
CVSD
to be
grounded.
This causes
the
CVSD
to produce a 6 kHz
square
wave output which is encrypted
and
transmit-
ted
via
the RF
synthesizer
and
the audio
driver
cir-
cuits. If a loop-around
BER
test
is
to
be
performed,
encrypted
data enters the Secure Com tester
via the
RF or line
inputs.
The
encrypted
data
is
then decoded
and the
resulting
plain text
sampled
by the
BER
com-
parison
circuit. If a
BER
test is to
be
performed
on
a
simplex
radio,
the
plain text out
of
the
radio's
decoder
is
sampled
with a probe
and
routed
into the
BER
com-
parison
circuitry.
T herefore,
plain
text
is taken
from
the
radio under test via a
probe,
or
from
the
R2004/
5D's
internal
decoder,
according to the
configuration
of
the R2004/5D.
When
the R2004/5D
is generating
in
RF
mode with the
duplex
generator off, plain text is
input from the
external
probe. When
the duplex gen-
erator
is
in RF
mode and
on,
plain text is
taken
from
the
internal
decoder.
When
the
R2004/5D
is
in
audio
mode,
plain
text
is
always
taken
from t
he internal
decoder
regardless of
the
duplex generator's
condi-
tion.
The
received,
decoded plain
text
from the radio
under
test
is
assumed to be a 6.0-kHz square wave.
This
is
not chopped
or
distorted
in any way, with an
amplitude of
8.0
to
10.0
volts
whenever the
BER
test
is
active.
Unless the
waveform presented
to
the BER
probe
meets
the preceeding requirements
of
fre-
quency
and
amplitude,
the
BER
test
will
not
work.
The
point inside
the
radios
which
must be probed
to
input
the
plain text data into
the
BER
test
circuitry
is
on the
CVSD.
This
point
is
the
CVSD
output
which
supplies
plain
text
to
be transmitted
(the
AID
out-
put),
and
should
be
available
in
all
Motorola
encrypted
radios.
When
the radios
are
in
t
he
receive
mode,
this
CVSD output supplies a
reclocked version
of
the
plain
text
out of the
decoder.
22 .6.2
DEVIATION MEASUREMENT
By the
pseudorandom
nature
of the
data
transmit-
ted
by Motorola
encrypted radios,
deviation measure-
ment
is
more
difficult.
This is
caused by
t
he
frequency
components
in
the
transmitted
data
stream.
The
Secure
Com tester offers
a more
accurate
deviation
measurement
with
a
new display. The deviation
mea-
surement
circuitry inside
the
standard R2001D
chas-
sis
is AC
coupled,
but
in the Secure Com test system,
the low
frequency
pole of this coupling
has
been
reduced,
yielding
a
more accurate
response
to
data
such as
that mentioned
above. The
manner in
which
the deviation
information is
displayed has also
been
enhanced for
this
particular
type of
measurement.
The
display
contains
two bar graphs,
each
centered at 4.0
kHz.
One represents
positive
deviation
and the other
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