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(2)
(f)
Decrease
the
rf
signal
to 1uV.
Check
that
a
1kHz
tone is
still
present at the speaker.
Transmit Audio
(1)
(a)
Inject
a 1kHz signal (25 mV)
through the uni-
(b)
(a)
versal connector. Key
the radio and
observe
the
service
monitor
scope
for
a symmetrical
sine wave.
If
the
signal appears distorted,
replace the synthesizer module, U300, and
retest.
Check
pins
21
and 22 of U102 for
3.5Vde
with
the radio
keyed. This voltage
turns
on
the
amplifiers
in
U102.
Using a 50Q probe, inject a 1kHz signal (0.5
to 1.0
Vac)
at
capacitor C23. Key
the radio
and
observe
the
service
monitor
scope
for
a
symmetrical sine wave.
(b)
Ensure
that the
signal
is
reaching pins
10 and
11
of
U101; the level
at pin 10 will be
consid-
erably lower than that at
pin 11.
Also, ensure
that the
signal
is
reaching pins
15, 16, and
22
of
U101.
(3) Inject 1kHz at
1
Vac
at
R16
(U101 side).
Key
the
radio and
observe
the
service
monitor
scope
for
a
symmetrical sine wave.
If
the
signal appears dis-
torted, replace the
synthesizer
module,
U300, and
retest.
(4)
This step checks
the quality
of
the
synthesizer's
output
signal.
All previous
steps
in
this procedure
should be performed before performing this step.
(a)
Inject
a 1kHz signal
(75 mV) through the back
connector. Using a
50Q
probe with a spectrum
analyzer, probe
pin
1
of
the
rf
PA, U202, and
key
the radio.
The
modulation on the carrier
and the carrier signal itself should
not
exhibit
"spurs" or parasitics.
If
this step fails,
go
to
the
Transmit Power procedure.
k.
Transmit Coded Audio
(SECURENET
radios only)
(1)
Replace
U900
with
a
SECURENET
bypass
mod-
ule
(NTN4720A).
Verify that the radio operates
properly
in
the
clear
mode.
(2)
(a)
(b)
Replace U900
with
a test
module.
Ensure
that
the transmitting and receiving units
have
the
same
encryption key.
Inject
a 1kHz signal (25mV)
through the uni-
versal connector. Place
the radio
in
the coded
mode.
Key
the radio and
observe
the
service
monitor for a
symmetrical eye pattern
with
4kHz
of
deviation.
(c)
Check
that
a 1kHz signal
is
present at U900,
pin 17.
(d)
Check
that an
eye
pattern is present at
U900,
pin
1.
(e) Using a properly equipped service
monitor or
test radio,
with the
same encryption key,
decrypt
the
coded signal and verify that a
1kHz signal
is
recovered.
27
(4)
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