©1995 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 12/14/02
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diameter
. The shank of a drill bit
makes a good tool for accurate coil
winding. The coil turns should be
spaced one wire diameter apart. The
coil is mounted vertically, as shown in
fig 2, with the bottom lead soldered to
a pc board pad, and the bottom of the
coil spaced just a little away from the
ground plane. Form the top lead over
to and insert into the top of ft cap C8
and solder.
g. Install C1, C2, and C3, orient-
ing as shown.
h. Install C7 and U1 in the holes
shown. The leads of C7 must be
formed to the narrower spacing of the
pads on the board.
i. Turn the preamp over, and ori-
ent it as shown in figure 3. Position
ferrite bead Z1 as shown. Note that
positioning the body of the bead
against the feedthrough capacitor
prevents its leads from shorting to
anything. Solder one lead to the in-
side metalization of ft cap C8, and
tack solder the other lead to the pad
for the left-hand lead of U1 as shown.
If there already is solder on the bot-
tom of C8, melt it and slide the lead
in.
j. Install tuned line L1, forming it
from #20 bus wire supplied. This coil
is actually just a straight length of
wire with legs bent at 90° to fit in
holes shown. Insert it from the bot-
tom of the board and adjust so the
part of the wire furthest from the
board is 1/16 inch from the surface of
the board.
Be sure that the coil leads are in-
stalled in the correct holes: the one on
the left should connect to the junction
of C1, C2, and gate 1 of the transistor;
the one on the right should connect to
the ground plane.
Then, solder both
leads and trim excess leads on top of
the board.
k. This completes construction.
Look over all compo-
nents and solder
connections. Check
for shorts or parts in
the wrong places.
INSTALLATION.
The preamp can
be mounted to any
flat surface. Simply
drill two 1/8 inch
holes 1-7/16 inch
apart, and attach the
preamp with 4-40
screws and standoffs
or spacers as desired.
Complete shield-
ing of the preamp is not required.
However, some care should be given
to selection of the mounting location
with regard to feedback from adjacent
receiver circuits or rf pickup if
mounted very close to a transmitter
circuit. Because the unit is small,
make sure that it isn't installed tight
against the rf amplifier or first mixer
of the receiver to minimize feedback
effects.
Connect the input and output ter-
minals in the receive signal path with
miniature coax, such as RG-174/u,
as shown in figure 2. Be sure to keep
the stripped pigtails as short as pos-
sible to maintain a 50
Ω
path. Connec-
tions are made by inserting the
stripped ends of the pigtails into the
pads on the board and soldering.
Normally, the preamp is mounted in
some sort of enclosure with UHF or
similar connectors on the enclosure
and miniature coax installed between
the preamp and the large coax con-
nectors. In some cases, the output of
the preamp can go directly to the re-
ceiver with the miniature coax.
/
Caution: Do not connect the pre-
amp in the transmit signal path.
Connect power supply lead to E5.
The LNW-450 requires fi10 to
15 Vdc. Current drain is about 10
mA.
Caution is
advised in se-
lecting a power
source. Solid
state amplifiers
can be dam-
aged by large
voltage tran-
sients and re-
verse polarity.
Although pro-
tection is pro-
vided in the
LNW-450 in the
form of a voltage regulator ic, avoid
such conditions as a matter of princi-
ple. Care should be taken especially
to install a reverse diode across any
inductive devices, such as relays, on
the same B+ line to absorb transients.
ALIGNMENT.
Factory assembled preamps are
tuned at 450 MHz. You may want to
retune the input circuitry to optimize
noise figure with the unit connected to
your antenna.
If you have built a kit, pretune the
variable capacitors as follows. The
capacitors have a solder blob which
attaches the metalization on the rotor
to the screw head. Note that maxi-
mum capacitance occurs with the sol-
der blob aligned with the flat end of
the capacitor. Start with C1 and C2
preset with the solder blob at the flat
end and C3 with the solder blob at the
round end.
Simply tune the input variable ca-
pacitors C1 and C2 for best reception
of weak signals. No test equipment is
necessary. If you happen to have ac-
cess to a signal generator and sinad-
der, they may be used; otherwise, just
do it by ear or watch an S-meter.
Tuning will be very broad.
Output capacitor C3 is adjusted
for maximum gain, i.e., strongest sig-
nal on receiver S-meter or other signal
strength indication. Sometimes, it is
easy to adjust this, too, by ear. At
450 MHz, C3 normally tunes close to
the round end, and tuning is neither
very sharp nor very broad.
If C3 wants to tune with the solder
blob all the way toward the round
end, you can stretch the turns of coil
L2 apart a little to reduce inductance.
If C3 wants to be all the way to the flat
end, you can compress the turns of L2
a little to increase inductance. If you
still can't make C3 peak within its
tuning range, check the dimensions of
L2. Make sure the inside diameter is
Figure 3. Bottom View of LNW-450 Board
Z1
L1
C8
C5
U1
DETAIL OF L1, SIDE VIEW
Figure 2. Top View of LNW-450 Board
E1
E2
C2
C1
C3
LONG DRAIN LEAD
SHIELD
C8
L2
Q1
R1
R2
U1
C7
GATE 2
SOURCE
GATE 1
E3
E4
E5
RF OUTPUT
COAX
RF INPUT
COAX
POWER
C5
DETAIL OF COIL L2, SIDE VIEW
