HAMTRONICS LNW-144 User manual

©1995 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered t
rademark. Revised:
10
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23
/
02
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Page
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FUNCTIONAL DESCRIPTION.
The LNW Preamp was designed as
a miniature low noise receiver pre-
amp. Being only 5/8" x 1-5/8", the
LNW conveniently mounts inside
many radios.
Models are offered for various vhf
& uhf bands. This manual covers
models shown in table 1.
The LNW uses a dual-gate mosfet
for low noise figure and good stability
under a wide range of load condi-
tions. Typical noise figure is 1.2 dB
and the output 1 dB compression
point typically is +5dBm.
Table 1. Preamps Covered By This Manual
Model Tuning Range Gain 3dB BW
LNW-144 120-150 MHz 16dB ±5 MHz
LNW-160 150-200 MHz 16dB ±10 MHz
LNW-220 200-270 MHz 16dB ±12 MHz
ASSEMBLY.
The following instructions will
help you build your preamp with a
minimum 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
operations. It is assumed that you
are an experienced vhf/uhf kit
builder and do not need basic kit
building instructions. If this is not
the case, consider having someone
more experienced 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 loca-
tions 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
circuit 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
solder 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 capacitor will settle onto
the board. If necessary to seat it, you
can press lightly on the metal base of
the capacitor 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 picking up the
transistor, and the use of a grounded
soldering iron is mandatory. A heat sink
is not necessary while soldering, 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 precautions above. The
transistors are all factory tested and
wrapped in anti-static bags to ensure that
they arrive in good condition. There is
no warranty coverage for damage which
occurs in construction 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°
angle 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
properly, 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
below board.
Note: The feedthrough capacitors
have a hollow center which is metalized
through from end to end. Therefore, 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 metali-
zation. It is not necessary for the lead to
go all the way to the other end because
there is metalization to conduct from one
end to the other.
Also note that the feedthru capacitor
by the transistor is not used as a feed-
thru 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 capacitor, and then solder all
three leads to the metalization in the
center of the capacitor. It is not nec-
essary to completely fill the capacitor
HAMTRONICS
®
LNW-144, LNW-160, LNW-220 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
ϖαλκ
819

©1995 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered t
rademark. Revised:
10
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23
/
02
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with solder 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 sol-
der the whole length of the shield.
Then, run a second bead of solder on
the other side of the shield. Solder-
ing on both sides of the shield pro-
vides maximum mechanical support
for the shield.
f. Install output coil L2 in the po-
sition shown. Form the lead to be
soldered to the pc board so the coil
fits within the edges of the board.
Insert the other lead in the center of
ft cap C8. Solder both leads of L2.
g. Install C1, C2, and C3, keeping
leads short as possible. C2 should
have the rounded end to ground.
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 bottom of C8, melt it and slide
the lead in.
j. Using #22 bus wire supplied
and the shank of a 1/8 inch drill bit
as a tool, wind coil L1 as shown. (It
doesn't matter which direction you
wind.) Consult the parts list for the
correct number of turns. Count com-
plete turns, from bottom to bottom.
For reference, the sample in figure 3
shows 5 turns.
After winding, use a knife to sepa-
rate the turns so they are not short-
ing together. The turns should be
barely spaced apart, just enough to
prevent shorting. Then, form the
ends of the leads so that the wire
coming off the bottom of the coil is
bent to go directly over to the holes
in the board. The bottom of the coil
should be 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.
k. This completes construction.
Look over all components 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 at-
tach the preamp with the 4-40
screws and standoffs or spacers as
desired.
Complete shielding 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 cir-
cuits or rf pickup if mounted very
close to a transmitter circuit. Be-
cause 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 ef-
fects.
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 possible to maintain a 50Ωpath.
Connections 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 be-
tween the preamp and the large coax
connectors. In some cases, the out-
put of the preamp can go directly to
the receiver with the miniature coax.
LCaution: Don't connect the preamp
in the transmit signal path.
Connect power supply lead to E5.
The LNW requires filtered +10 to 15
Vdc. Current drain is about 10 mA.
Caution is advised in selecting a
power source. Solid state amplifiers
can be damaged by large voltage
transients and reverse polarity. Al-
Figure 2. Top View of LNW 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
Figure 3. Bottom View of LNW Board
Z1
L1
C8 C5 U1

©1995 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered t
rademark. Revised:
10
/
23
/
02
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Page
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though protection is provided in the
LNW in the form of a voltage regula-
tor ic, avoid such conditions as a
matter of principle. Care should be
taken especially to install a re-
verse diode across any inductive de-
vices, such as relays, on the same B+
line to absorb transients.
ALIGNMENT.
Factory assembled preamps are
tuned at the center of the band. The
bandwidth is wide enough so that re-
tuning normally is not necessary be-
cause of frequency. However, you
may want to retune the input cir-
cuitry to optimize noise figure with
the unit connected to your antenna.
Simply retune the input variable ca-
pacitor for best reception of weak
signals. No test equipment is neces-
sary. If you happen to have access to
a signal generator and sinadder, they
may be used; otherwise, just do it by
ear.
TROUBLESHOOTING.
Since the unit is fairly simple,
troubleshooting usually is limited to
checking the dc voltages on the tran-
sistor. These will vary somewhat;
however, in general, the gate-2 volt-
age should be about 4 Vdc, and the
drain should be at about 8 Vdc. The
source and gate 1 should be at
ground potential.
If the dc voltages are OK but the
unit is no longer amplifying, assum-
ing there are no problems in the coax
cabling, the transistor may have been
damaged by transmitter rf or light-
ning discharge at the antenna. Such
damage often does not cause a
change in the dc characteristics of
the transistor.
If the drain voltage is much lower
than 8Vdc, first disconnect ferrite
bead Z1 to see if the transistor is
shorting the output of the voltage
regulator. In the case of a severe
voltage transient or reverse B+ volt-
age, it is possible to also damage the
voltage regulator.
If the unit is amplifying OK but
you are experiencing intermod, you
may be overloading your receiver by
adding gain ahead of the rf stage.
Low noise preamps are effective in
improving sensitivity of receiver sys-
tems in weak signal areas. However,
it is normally considered inadvisable
to use a preamp, even with a well de-
signed receiver, in very strong signal
areas, such as the center of a city or
other locations with high powered
transmitters in the area.
Adding gain ahead of a receiver
degrades the selectivity of a receiver
by an equivalent amount by boosting
undesirable signals as well as desir-
able ones. In severe cases, strong
signals which do not cause intermod
by themselves will create intermod in
the rf stage or mixer of your receiver
after being amplified an additional 20
dB.
If you use a preamp with a re-
peater receiver, you will need to have
additional rejection in your duplexer
to attenuate your transmit signal
that much more to prevent desense.
TRANSISTOR
REPLACEMENT.
Transistor replacement is compli-
cated a little by the fact that the pc
board has plated-through holes. You
must remove all the solder from the
drain and gate-1 leads before trying
to pull the transistor off the board.
This can be done with solder-wick or
a vacuum desoldering tool, as long as
you remove all the solder within the
holes. Then, melt the solder on the
top of ft cap C5, and lift the gate-2
lead of the transistor.
LCAUTION: The small geometry
and high impedances make fet's heat
and static sensitive; so be careful. It is
good to discharge your hand to a
grounded metal object just before picking
up the transistor, and 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
transistor if you
observe the pre-
cautions above.
The transistors
are all factory
tested and
wrapped in foil to
ensure that they
arrive in good
condition. There
is no warranty coverage for damage
which occurs in handling.
Refer to ASSEMBLY section of
manual for details of how to install a
transistor.
REMOVING OTHER PARTS.
Because the pc board uses plated
through holes, all of the solder
within the holes must be removed be-
fore a lead can be removed from the
board. This can be done with solder-
wick or a vacuum desoldering tool, as
long as you remove all the solder
within the holes.
Z1
L1
Figure 4. LNW Preamp, Schematic Diagram
8-VOLT REG.
U1
E5
B+
(10-15V)
C7
R1
R2
E3
E4
INPUT
RF
C5
C1 C2
Q1 L2
C8
C3
E2
E1
OUTPUT
RF

©1995 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered t
rademark. Revised:
10
/
23
/
02
-
Page
4
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PARTS LIST.
Ref # Description
C1 6 pf disc (LNW-144 & 160)
2 pf disc (LNW-220)
C2 20 pf cer. variable (144 & 160)
4.5 pf cer. variable (LNW-220)
C3 .001 µf disc (1nK or 1nM)
C4 not used
C5 .001µf feedthrough capacitor
C6 not used
C7 0.15µf mylar capacitor
C8 .001µf feedthrough capacitor
L1 #22 bus wire 1/8 inch i.d. with
turns barely spaced apart.
LNW-144 & LNW-220: 5 turns
LNW-160: 4 turns
L2 0.33µH molded coil
(orn-orn-sil-red)
Q1 N.E.C. 3SK122 mosfet
R1-R2 100K
U1 78L08 Voltage Regulator IC
Z1 Ferrite Bead