RADIOBEACON TRANSMITTER
ND500II (125 WATTS) DOUBLE SIDEBAND - NO VOICE
Page 5-12
15 September 2003
(m) Repeat steps (c) through (l) until shutdown
delay period requirements in step (h) are met
without further adjustment of
DELAY
potentiometer A5R41.
(n)
Remove digital multimeter from A11TB1-17.
5.3.9
HIGH SWR CUTBACK
THRESHOLD CHECKS
: Verify the high SWR
cutback threshold is set to the level that represents a
reflected power of 14 watts, as follows:
(a)
Verify the requirements of paragraphs 5.3.2
through 5.3.4 have been completed.
(b)
Set
O/P PWR
potentiometer A4R31, on
modulator driver PWB, fully counter
clockwise.
(c)
Set switches, except
POWER
switch S3, as
tabulated for
Calibration Setting
in table 4-1.
Set
POWER
switch S3 to
OFF
.
(d)
Interchange forward and reflected outputs of
harmonic filter A7, as follows (refer to figure
MD-5 to locate harmonic filter A7 and to figure
MD-12 to locate A7TB6).
-
Disconnect insulated conductor of coaxial
cable #76 from A7TB6-1.
-
Disconnect insulated conductor of coaxial
cable #77 from A7TB6-3.
-
Connect insulated conductor of coaxial
cable #76 to A7TB6-3.
-
Ensure insulated conductor of coaxial #77
is not in contact with any conductive
object.
(e)
Connect a digital multimeter, set to measure
resistance, between A11TB1-18 and ground.
(f)
Set
TEST
switch S6 to
REFL PWR
.
(g)
Set
POWER
switch S3 to
ON
.
(h)
Reflected power indication on
TEST
meter M1's
upper scale should be zero watts and
SWR
ALARM
lamp DS6 shall be off.
(i)
Digital multimeter indication shall be infinite
impedance (open circuit).
(j)
Slowly adjust
O/P PWR
potentiometer A4R31
clockwise until
SWR ALARM
lamp DS6 just
turns on.
(k)
The RF output, as indicated by dummy load's
power indicator, shall be 14 watts.
(l)
If requirements of step (k) are met, proceed to
step (p); if they are not met, complete steps (m)
through (o).
(m) Set
SWR THRESH
potentiometer A5R69 fully
clockwise.
(n)
Adjust
O/P PWR
potentiometer A4R31 for an
RF output of precisely 14 watts, as indicated by
dummy load's power indicator.
(o)
Slowly adjust
SWR THRESH
potentiometer
A5R69 counter clockwise until
SWR ALARM
lamp DS6 just turns on.
(p)
Reflected power indication on
TEST
meter M1's
upper scale should be 14 watts.
(q)
If necessary, adjust
REFL PWR CAL
potentiometer A5R80 to meet the requirements
of step (p).
(r)
Digital multimeter indication shall be zero ohms
(short circuit).
(s)
Simultaneously monitor
TEST
meter M1's
reflected power indication and continue to
adjust
O/P PWR
potentiometer A4R31.
(t)
Reflected power indication on
TEST
meter M1
shall not increase significantly beyond 14 watts
as
O/P PWR
potentiometer A4R31 is adjusted
clockwise.
(u)
Set
O/P PWR
potentiometer A4R31 fully
counter clockwise.
(v)
SWR ALARM
lamp DS6 shall turn off.
(w)
Set
POWER
switch S3 to
OFF
.
