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When the antenna impedance has greater variance from 50 Ohms, it may be the case that the PA cannot
deliver the full power 2500W (3500W), or some of the protection circuits may be automatically activated.
In such cases we recommend doing a manual tuning.
The best indication of proper PA tuning is the Screen Current. In the properly tuned PA this should be
within 0 to + 20mA (0 to +30mA) (at full output power).
Tuning procedure:
•
Set band switch with knob BAND at proper position and set knobs TUNE and LOAD at position
according Tuning table
NOTE:
Set input power to about 25 watts to begin.
•
Press PTT and apply input power from TCVR, check the Ig2 (
I
Screen on the display
). If it is ok
(bellow +20mA), gradually increase the input power until the PA reaches about 70% of its
maximum output power.
•
Using the TUNE knob, adjust for maximum FORWARD POWER while monitoring the Screen
current.
•
When the Screen current e30mA, adjust the LOAD knob to decrease Screen current to
about 0 mA. Readjust TUNE for maximum FORWARD POWER.
•
Increase the PA input power until you reach the desired maximum output power. Keep watching
the Screen current. If the Screen current e30mA decrease it by using the LOAD knob.
•
Repeat using the TUNE knob to reach desired maximum FORWARD POWER and check Screen
current.
•
If the Screen current is lower than 0 mA (negative value), change it by turning the LOAD button
until 0 mA is set and check again for maximum output power. Do not start with very low input
power, set abt. 50% before beginning tune process.
•
If you reached the desired maximum output power, and the PA Screen current is inside 0 / +20mA
(30 mA) , then tuning process is finished.
Notice 1:
If the tuning process takes more than 1 minute, allow for a short break to prevent temperature
overloading of the PA.
Notice 2:
If you use the PA with the output power adjusted lower than the maximum settings, screen
current can take negative values. There is no need to readjust the PA, it is still working in the linear mode.
