OM POWER OM2500 A-F, Instruction Manual

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5.3. Tuning of Power Amplifier
The OM2500A-F amplifier is operated in class AB. Thus it’s possible to obtain a maximum
output power at excellent linearity. For this purpose the amplifier has to be tuned carefully.
WARNING!
Before starting tuning you have to check if the right antenna or a 50 Ohms load
resistance is connected at the antenna output!
CAUTION
The operation of a mistuned PA will cause malfunctions, the increase of grid current
(the GRID-MAX-LED will light up) and problems with TVI/BCI.
CAUTION
The grid-current is shown with 2 LED diodes. It’s normal if the green LED is flashing or
may be shining a little bit during peak operation. If you overload the amplifier the
output power increases the grid current at very small rates and the red GRID-MAX-
LED is shining and the safety devices switch the PA to STBY. You must decrease the
input power.
CAUTION
In SSB mode you will have good output power if the green LED lights up a bit. The
current of screen grid is measured and shown in a Bar graph Indicator. The amplifier
has to be tuned in such a way that the current is between - 20 mA to +50 mA. At
currents beyond these values the operating point will be shifted and IM-products will be
rapidly increased. If a value of + 70mA is exceeded, the safety devices will switch the
amplifier to STBY mode.
5.3.1.
AUTO or MANUAL
There are two possibilities of operation mode in OM2500A-F – AUTO or MANUAL.
Normally, when you are using CAT interface connection between TCVR and PA, in AUTO
mode PA will tune automatically to the TCVR frequency. If you do not have or use CAT
connection, you will use MANUAL mode. You must manually select proper band and
segment, corresponding to TCVR´s band and frequency. Then OM2500A will tune
automatically to this manually selected band/segment.
5.3.2.
Manual tuning instructions
OM2500A-F has been design to deliver maximum output power at 50 Ohms load. Parameters
for PA auto tuning using real 50 Ohm loads are stored in the memory (
factory default ). To
deliver maximum output power to a real load you need to adjust the tuning according to your
real antenna impedance.
This has to be done manually in TUNE mode ( see 5.3.3. for
details ). First off all PA must be switched on.