©1995 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised:
11/27/01
- Page 2 -
l. Tack solder electrolytic capaci-
tor C12. Bend the leads at right an-
gles, and observe polarity.
m. Tack solder R1 and L2 as
shown. Ferrite bead Z1 is installed on
the ground lead of choke L2.
n. Check to be sure all parts are
installed according to pa rts list, and
check all solder connections.
RF INPUT/OUTPUT
CONNECTIONS.
The input and output connections
are made with RG-174/u 50-ohm coax
cable connected to the appropriate in-
put and output pads and ground plane
of the pc board. Lengths shown as-
sume that PA will be installed in REP-
200 Re peater or an A16 RF Tight Box.
Connect cables by stripping as il-
lustrated and tack-soldering to board.
Note that stripped length of coax is
inductive; so keep leads short and
neat.
Connect the shields by pretinning
all around the shield and then tack
soldering just the part of the shield
which contacts the board. Avoid melt-
ing polyethelene insulation on cable
by pretinning board and cable and
then tacking them together quickly.
POWER CONNECTIONS.
+13.6Vdc should be connected to
the B+ pad at the top of the pc board.
When installed in an REP-200 Re -
peater, a hookup wire should be at-
tached to the B+ pad as shown, using
a ferrite bead on the far end, which
attaches to the feedthrough capacitor
in the PA compartment.
A ground return cable should be
connected from the power supply to
the ground plane of the pc board
through the mounting hardware. The
cable should be #18 or larger wire to
mini mize voltage drop. A 3 or 4 Amp,
quick acting fuse should be connected
in the positive supply line for protect-
ion.
A well regulated power supply
should be used. Current drain of the
PA at full output is about 2 Amp.
Note that the output capability of
the PA drops rapidly as the voltage is
reduced below 13.6Vdc; therefore, you
should try to use a power source of
sufficient voltage and minimize cable
losses so that you have full B+ avail-
able at the PA.
CAUTIONS TO PROTECT
TRANSISTORS.
Because it is so easy to damage rf
power transistors in the field due to
accidents and abuse, transistor
manufacturers do not provide any
warranty to cover replacements once
a transistor is installed in the unit.
They test them thoroughly at the fac-
tory be cause they are expensive parts
and they want to be sure you get good
parts with your kit. Therefore, they
do not honor claims that "the transis-
tor must have been bad from the fac-
tory".
For your protection, please be
sure to observe the following precau-
tions:
1. Transistors are made to oper-
ate in specific circuits. Do not try to
check with ohmmeter, etc. Some-
times, you can blow a transistor when
you reverse polarity.
2. Sometimes, transistors may be
destroyed by parasitic oscillations oc-
curring during tuning be cause of the
e xtremes of capacitor settings, or due
to accidental shorting of components.
To protect against such damage as
much as possible, turn power supply
voltage down to 9 or 10 Volts when you
first apply power until the unit is
tuned. Then, turn up to full 13.6Vdc.
Of course, final tuning should be done
at full 13.6V.
3. Never exceed 13.6Vdc, as even
a small over-voltage causes strain on
transistors.
4. Be sure you have a low imped-
ance connection to the power supply,
i.e., short, heavy cable.
5. Do not attempt to operate PA
until exciter has been properly
aligned by itself, operating into a
50-ohm load.
ALIGNMENT.
Alignment is very simple. Con-
nect the input to an exciter which
has already been tuned into a 50-ohm
dummy load. Connect the output to a
50-ohm load of sufficient power rat-
ing. Use an in-line power meter, or
monitor output with a dc voltmeter
connected to rf detector test point pad
on pc board.
Preset variable capacitors as fol-
lows if this is the first time tuning
from a kit; otherwise, they should be
left where previously tuned. The
large mica variable capacitor should
be screwed down tight and then
backed off about three turns. The pi s-
ton trimmer capacitors in the output
circuit should be adjusted so that
5/16 inch of piston screw is exposed
at top. The piston trimmer capacitors
in the input circuit should be ad-
justed so that 1/2 inch of piston
screw is exposed at top.
Apply B+ and moderate rf drive.
First, adjust mica variable capacitor
C6 for maximum output. Then, al-
ternately tune the various mica and
piston trimmer capacitors for maxi-
mum output. Continue repeaking
capacitors until maximum output is
achieved and all interactions between
capacitors are worked out.
Note: If the output is less than 8-10
Watts, check to be sure that the input
tuned circuits are not tuned to a false
peak, which can happen if the piston
capacitors in the input circuit are ad-
justed with only about 1/4 inch of pis-
ton exposed. The true peak (assuming
operation in the 440-470 MHz range)
will occur with about 1/2 inch of piston
exposed.
If you happen to have a spectrum
analyzer (not required), you can fine
tune C8 for lowest harmonic level and
repeak C6 and C7 for maximum; oth-
erwise, just peak all the capacitors for
maximum output.
Note: Do not retune exciter with PA
connected. Once the exciter is tuned
into a 50-ohm load, it should never be
tuned again. Tuning the input of the PA
takes care of matching the PA to the ex-
citer.
OPERATION.
Operation is quite simple. B+ can
be applied all the time if de sired.
Merely apply an rf signal to the PA
when you want to transmit. Power
output may sag about 5% as the tran-
sistor heats up, but no more. If ex-