©1999 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 5/3/04
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connected.
Driving source should be
tuned into 50 ohm load and left alone
afterwards. Input of PA is tuned then
to present 50 ohm load to driver.
d. Apply drive to PA, and alter-
nately adjust C1/C8 and C2/C3 for
maximum output. Do this several
times to work out any interactions.
Use an insulated tool.
e. When fully tuned, the PA
should deliver about 45 to 55 Watts
with 13-15 Watts drive when using a
13.6Vdc power supply. If the dc volt-
age is low, the output will be less.
You may also experience a little loss in
the output coax if it is not a good low-
loss type. The PA will draw about 6 to
7 Amp at full output.
MOUNTING.
There is no special way to mount
the PA. However, for repeater service,
complete shielding is required. There-
fore, some sort of enclosure should be
used which would leave just the fins
of the heatsink on the outside.
POWER.
The RPA-402 requires well-
regulated 13.6Vdc, free of transients,
at about 6 to 7 Amp. An 8 Amp con-
tinuous-duty power supply would
have some reserve. Use fairly short,
heavy leads to connect power supply
to the pc board. If there are any re-
lays or other inductive devices on the
same power supply, be sure to put a
reverse diode across the device to ab-
sorb reverse voltage spikes generated
by inductive kick-back. It would be
wise to connect an 8 Amp, fast-acting
fuse in series with the PA power lead if
the power supply is capable of more
than 8 Amps.
CAUTION: RF power transistors are
fully tested by the manufacturer and
are not guaranteed because they are
easily damaged by physical or electri-
cal abuse.
They are very expensive to
replace. Be sure to use adequate pre-
cautions to avoid damage.
OPERATION.
Once tuned, the RPA-402 will
automatically operate when sufficient
drive is applied. Since it operates
class C, it will draw no current when
no rf power is applied. It is designed
for continuous duty at up to 55 Watts.
Do not operate it above that level.
Reduce drive if necessary so it will op-
erate at this level, which is sufficiently
conservative if heatsink is not blocked
and ambient temperature is below
100 degrees F.
REPAIR.
Should it be necessary to replace
the transistor, be sure to use an exact
replacement. To remove old transis-
tor, carefully peel each lead away from
the pc board while applying heat to
melt solder. Then, remove transistor
from unit, and clean excess solder
from board. This is important to
avoid tearing leads from new transis-
tor when hardware is tightened. Also,
clean off old heatsink compound,
which may be dirty, and apply a fresh
coat to the new transistor. Remember
to resolder any components removed
for access to transistor.