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(3)
(4)
(5)
(1)
26
approximately
0.68V
(mid-band and vhf) or
0.4pV
(uhf) for 12dB
SINAD.
If
a
good reading
was
obtained, continue with
the next step (mid-band and vhf) or
go
to
step
g (2) (f) (uhf);
if
the reading
was less
than
12dB
SINAD, go
to
step g (3).
(c)
(For
mid-band radios only). Using a 50Q
probe, inject the carrier frequency at pin
1
of
rf
amplifier module U1;
use
pin
11
of
U203
for
probe ground.
The signal level
should be
approximately
0.27uV
for
12dB
SINAD.
(d)
(For
vhf radios only). Using a 50Q probe,
inject the carrier frequency at
pin
11
of two
pole filter U1; use
pin
2 of U203 for probe
ground.
The signal
level should be approxi-
mately
0.27,V
for
12dB
SINAD. Check
that
the
TUNING
VOLTAGE
level at U1,
pin
5, is
0.7Vdce
at 146MHz.
(e)
(For
vhf radios only).
Check
the bias
voltages
at the
rf
amplifier,
Q3.
If
these voltages are
incorrect,
suspect T1.
(f) Using
a 50Q
probe, inject the carrier frequen-
cy
at
pin 12 of
U203; use
pin
11
(mid-band
and vhf) or
pin
13
(uhf) of U203 for probe
ground.
The signal
level should be approxi-
mately
0.27pV
for
12dB
SINAD.
(g) Check
the
dc voltages
of U203.
(h)
Replace
the
FDS
module, U203, and repeat
step g (2) (e).
Using a frequency counter
with a
50Q probe,
check
the synthesizer's input
(U300,
pin
32)
to the
2nd
LO,
using the ground side
of
CR800
for
ground.
The
reading should indicate
53.1MHz
or
54.0MHz (mid-band
and
vhf),
or
72.9MHz
or
73.8MHz
(uhf).
Using
a 50Q
probe, inject
53.55MHz
(mid-band
and vhf) or
73.35MHz
(uhf)
at
inductor
L1; place
the positive end of the probe where
C46
and
L1
connect. Use the ground screw
of the front end
module (vhf), the ground pin (pin 5) of U4 (mid-
band),
or pin 3 of
J2
(uhf) for probe ground.
The
signal level should be approximately 90
to
100uV
(mid-band and vhf)
or
1.2uV
(uhf) for 12dB
SINAD.
Using a 50Q
probe, inject
450kHz
at filter
pin
1
of
FL3
(mid-band and vhf) or
pin
1
of U2 (uhf).
Use
pin
2
of
FL3
(mid-band and vhf) or
a screw
head
(uhf) for probe ground.
The signal
level should be
approximately
3.5uV
for
12dB
SINAD.
If
this step
fails, go
to
the
Receive
Audio procedure.
h.
Receive Audio
Using a 50Q probe, inject
450kHz
at filter
pin
1
of
FL3
(mid-band and vhf) or
pin
1
of
U2 (uhf).
Use
pin
2 of FL3 (mid-band and vhf)
or
a screw
head
(uhf) for probe ground.
Set
the
input
signal level at
-60dBm.
Set
the radio to rated audio
(3.7Vac)
and
measure
the distortion level.
If
the distortion level
is greater than
5%,
or
3.7 Vac cannot be obtained,
continue
with
this procedure.
(2) (a)
Check
the
voltages
of the i-f IC,
U100 (volt-
ages
are approximate):
pin
8 =
4.5Vdc;
pin
9
1.5Vde;
pin 10
0.9Vde;
and
pin 12
= 1.5Vdc.
These voltages
determine
if
the op
amps
in
the IC are functional.
If
the
voltages are cor-
rect, continue the procedure.
(b) Ensure that the
No.1
regulator voltage is not
below
4.8Vdc
when set
to rated
audio.
NOTE
The
current drain should be approximately
200mA at
rated audio.
(c)
Inject
450kHz (-60dBm)
at
pin
1
of
FL3
(mid-
band and vhf) or
pin
1
of U2 (uhf).
Check
the
discriminator output (U100,
pin
31)
with an
oscilloscope
for a
symmetrical sine wave.
When
no
signal is applied, the reading should
be
3.5Vac
of
noise.
If
the result is not
symmet-
rical or
if
the
signal is
low,
check
resistor
R3.
(3) (a) Inject
a
modulated
1kHz signal (-30dBm) at
capacitor C14. Adjust
the radio for rated audio
and measure the distortion level.
(b) Vary the volume level and monitor the audio at
capacitor C22. The signal should
not "clip"
until
approximately
4.0Vac.
NOTE
If
the audio
processing
bit
has been set
or
tuned lower, the audio will clip at
a
lower levei.
This
will
affect distortion measurements.
(4) (a) Inject
a
modulated
1kHz signal (-30dBm) at
capacitor
C22.
Adjust the
radio for rated audio
(3.7Vac)
and measure the distortion level.
(b)
Check
pins 4, 28, and
31
of
U102
for
6.5Vac
p-p. At maximum volume, the waveform
should be clipped.
i.
Receive 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) Replace U900
with
a test
module.
Ensure
that
the transmitting and receiving units have the
same
encryption key.
(b)
Set
the
service
monitor or
rf
signal generator
to output
a
1-millivolt
signal.
Introduce the
sig-
nal to the radio at the
exact channel frequency
through the universal connector. Modulate the
rf
signal
with an
encrypted 1kHz tone at
4kHz
deviation.
Set
the volume control for rated
audio output (3.74Vrms).
(c)
Check
that a 1kHz tone is present at the
speaker.
(d)
Check
that an
eye
pattern is present at
U900,
pin
2.
(e) Check
that
a 1kHz signal
is present
at U900,
pin
3 and U101, pin 7.
h.
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