351804-1 Rev. 100
COM5000-8 TECHNICAL MANUAL
40
1.25kW PA Module
RF OUTPUT
“T” connector (direct at Wattmeter)
Connector
h)
Starting with a low RF output level from the RF Signal Generator increase the generator level until
the forward power reading is 500W.
i)
Measure the voltage on U20-1 (VF). Adjust VR5 so the voltage measured on U20-7 is equal to the
voltage at U20-1.
j)
Measure the voltage on U20 pin 7. Adjust VR7 such, that the voltage measure on U20 pin 10 is 1/2
of the voltage measured on U20 pin 7.
k)
Un-key the system. Set up for operation into
one 50 Ohm load
.
l)
Key the system. Increase the RF drive level to obtain an output power of
1250 W
.
m)
Proceed to perform this adjustment on the PA Controller PCB Assembly with
1250 W
output:
VF
:
Set VR6 for a reading of 2.00 V measured on U20A pin 1.
VFL:
Set VR8 for a reading of 1.00 V measured on U2 pin 3.
DRVR Q1FLT Window Comparator:
This adjustment requires the Driver bias current adjustment to have been completed. See paragraph
5.4.1.4.
a)
Operate the PA Module as
a “stand alone” Amplifier – while still part of the Transmitter - as
described in section 5.4.1 above.
b)
Turn ON the System. With the system un-keyed, measure and record the DC voltage on U17 pin 4.
c)
Measure the DC voltage at U17 pin 5 and adjust VR9 for a voltage
0.05 V
below the voltage
measured on U17 pin 4.
d)
Select an operating frequency of 29.9 MHz and key the transmitter
e)
Adjust the RF Signal Generator level to obtain a power output of 1250 W. Wait for the initial drift in
power to settle in order to get a reasonably stable
1250 W power.
f)
Measure and record the DC voltage at U17 pin 9.
g)
Measure the DC voltage at U17 pin 8 and adjust VR10 for a voltage
1.5 V
below the voltage
measured at U17 pin 9.
50 Ohm
Load
50 Ohm
Load
Wattmeter
