©1995 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 12/14/02
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FUNCTIONAL DESCRIPTION.
The LNW-450 Preamp was de-
signed as a miniature low noise re-
ceiver preamp. Measuring only 5/8" x
1-5/8", the LNW-450 conveniently
mounts inside many radios.
The LNW-450 uses a dual-gate
mosfet for low noise figure and good
stability under a wide range of load
conditions. It is tunable in the range
of 400-500 MHz and has a nominal
gain of 18 dB. Typical noise figure is
1.5 dB and the 1 dB output compres-
sion point typically is +5dBm.
ASSEMBLY.
The following instructions will help
you build your preamp with a mini-
mum of effort. It is a miniature unit,
though; so precise construction is
necessary to get all the parts in the
proper positions.
The steps which follow are meant
to serve as a general guide as to the
construction sequence and critical op-
erations. It is assumed that you are
an experienced vhf/uhf kit builder
and do not need basic kit building in-
structions. If this is not the case,
consider having someone more ex-
perienced help you.
During construction, refer to the
diagrams and parts list for details.
Note that not all the holes in the
board are used for this model. Other
frequency ranges use slightly different
circuitry. The illustrations clearly show
the locations of the parts to be installed
and the empty holes.
a. The side of the pc board which
has mostly ground plane is the top of
the board. The bottom of the board
has several conductor patterns for cir-
cuit connections.
b. Install feedthrough capacitors
C5 and C8 as shown in figures 1 & 3.
Insert them from the
BOTTOM
of the
board with the tapered part toward
the board. Hold the soldering iron at
the base of the capacitor until the sol-
der on the capacitor melts. Once the
solder melts at one point, it is easy to
get all the solder to be molten at one
time by running the iron around the
edge of the capacitor. Then, the ft ca-
pacitor will settle onto the board. If
necessary to seat it, you can press
lightly
on the metal base of the capaci-
tor with the soldering iron once the
solder is melted; but do not press on
the ceramic center of the capacitor.
Note that there may be a third 1/8
inch hole on the board, which is not
used in this model. The source of the
fet is connected directly to ground; so
the hole next to the source is not
used. An extra feedthrough capacitor
is supplied in case you damage one.
CAUTION: The small geometry and
high impedances make FET's heat and
static sensitive; so be careful. It is
good to wear a grounded wrist strap, or
at least discharge your hand to a
grounded metal object just before pick-
ing up the transistor. The use of a
grounded soldering iron is mandatory.
A heat sink is not necessary while sol-
dering, but be careful not to apply any
more heat than necessary. You should
not be overly anxious about blowing
out the fet if you observe the precau-
tions above. The transistors are all fac-
tory tested and wrapped in anti-static
bags to ensure that they arrive in good
condition. There is no warranty cover-
age for damage which occurs in con-
struction or handling; but replacement
transistors are moderately priced.
c. Figure 2 shows the placement
of Q1 on the board. The drain is the
long lead. Figure 1 shows how to
form the leads.
Pick up the transistor and orient it
as shown in figure 2
with lettering up
.
Make sure you know which lead is
which. Gently bend the source, gate
1, and drain leads down at a 90° an-
gle as shown in figure 1. Then, bend
the bottom of the source lead out
away from the transistor to form an
"L" shaped foot. When formed prop-
erly, the transistor will sit flush with
the board as shown. (The gate 2 lead
is not bent.)
Insert the drain and gate 1 leads
through the holes in the board. The
foot formed in the source lead should
rest on the top of the board as shown
in figures 1 and 2. Tack solder the
foot of the source lead to the board.
Check that the transistor is down
against the board as shown in figure
1. Check again that the transistor is
oriented properly with the lettering up
and the long lead in the hole for the
drain. Then, solder the gate 1 and
drain leads to their pads under the
board. Trim off end of drain lead be-
low board.
Note: The feedthrough capacitors
have a hollow center which is metal-
ized through from end to end. There-
fore, in order to make a connection to
the feedthru capacitor, simply insert a
short length of the lead into the hollow
center of the feedthru and solder to the
metalization. It is not necessary for the
lead to go all the way to the other end
because there is metalization to con-
duct from one end to the other.
Also note that the feedthru capacitor
by the transistor is not used as a
feedthru cap in the normal sense; it is
merely used as a very good vhf/uhf
bypass capacitor and tie point.
d. Install vertical resistors R1 and
R2 in the holes shown in figure 2.
Solder their bottom leads. Then, refer
to figure 1 and bend the top leads
over, inserting them into the center of
ft capacitor C5. Trim these leads off
at the bottom. Bend the fet gate 2
lead over to touch the top of the ft ca-
pacitor, and then solder all three
leads to the metalization in the center
of the capacitor. It is not necessary to
completely fill the capacitor with sol-
der as long as the three leads are all
soldered at the top.
e. Solder metal shield to ground
plane on top of pc board in position
shown in figure 2. Keep the shield as
close as possible to the transistor to
leave room for output coil L2. First,
tack solder the shield to the board at
each end. Once the shield is aligned
properly, run a bead of solder the
whole length of the shield. Then, run
a second bead of solder on the other
side of the shield. Soldering on both
sides of the shield provides maximum
mechanical support for the shield.
f. Output coil L2 is 3-1/2 turns of
#20 bus wire wound on 7/64"
inside
HAMTRONICS® LNW-450 UHF RECEIVER PREAMP:
ASSEMBLY, INSTALLATION, & MAINTENANCE
GATE 1
SOURCE
GATE 2
Figure 1. Transistor Lead Formation
LETTERING
MUST BE UP
GATE 2
SOURCE
GATE 1
DRAIN
IS LONG
LEAD
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