©1999 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 4/22/03
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Figure 1. LNY Preamp, Parts Location and Schematic Diagrams
OPERATION.
The LNY series preamps operate in
linear mode; so they may be used to
receive any mode of transmission,
including ssb and atv.
Low-noise preamps are effective in
improving sensitivity of receivers 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 large
city or other locations with high pow-
ered transmitters on all sorts of fre-
quencies.
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
amount by the preamp.
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.
ALIGNMENT.
Units are factory aligned at the
center of the band, and they are easily
readjusted if your operating frequency
is near one end of the band or the
other instead of being near the center.
If retuning is necessary, simply retune
the variable capacitor(s) for best re-
ception of weak signals. No test
equipment is necessary. If you hap-
pen to have access to a signal genera-
tor and sinadder, they may be used;
otherwise, just do it by ear.
Note that for uhf units, it may be
necessary to spread the turns of the
coils to allow alignment for the high
end of the band. If the variable ca-
pacitors peak with the capacitor at
minimum capacitance (toward round
end of cap), spread the corresponding
coil turns to decrease inductance.
That should allow the variable capci-
tor to tune within its range.
The lower frequency units have
only one adjustment capacitor. The
higher frequency models have multi-
ple capacitors to tune; for those, al-
ternately adjust pairs of capacitors
seeking the best
combination of
settings.
TROUBLE-
SHOOTING.
Since the unit
is fairly simple,
troubleshooting
usually is limited
to checking the
dc voltages on the
transistor. These
will vary some-
what; but, in
general, the
source voltage
should be 0Vdc,
gate-2 should be
about 3.5 to
4Vdc, and the
drain should be
8Vdc. Current drain should be no
more than 20 mA (10mA typical).
The two common failure modes,
caused by excessive rf or dc voltage
transients,
may
cause the gate-2 volt-
age to be quite low or the same as the
drain of the transistor, indicating an
internal short. Generally, dc power
line problems, such as transients
cause a drain to gate-2 short and high
rf fields or lightning coming in the
antenna connector usually cause a
gate-1 to source short. The latter
usually doesn’t show up as a change
in dc voltage because gate-1 is con-
nected to dc ground in the circuit. A
sudden loss of sensitivity with no
change in dc voltage usually indicates
damage to the input gate (gate-1).
Note that the two gates have built-in
diode protection, but diodes will only
withstand a limited surge; beyond
that, the diodes will be damaged along
with the FET.
CAUTION:
FET's are static sensi-
tive. If replacement is necessary, be
sure to ground your wrist before han-
dling them. Internal diode protection
will reduce, but not eliminate, risk.
Devices also are heat sensitive; so
don't apply soldering iron longer than
necessary. If FET is replaced, be sure
to orient as shown with the source
lead being the wide one.
Often times, the best way to re-
move surface mount devices from a
board are to cut the part up, removing
the leads individually and then unsol-
dering them.
PARTS LIST, COMMON
PARTS FOR ALL MODELS.
Ref #
Value (marking)
C3,C4
.001 µf chip cap.
C7,C8
.001 µf chip cap.
D1 1N4148
diode
J1,J2
RCA jack (rf type)
Q1
Philips BF-998 MES FET
R1 620
Ω
chip resistor
R2, R3
86K chip resistor
R4 47
Ω
chip resistor
U1
78L08ACD voltage regul.
Parts List, Parts which change with Frequency Band.
Model C1 C2
L1
L2
C5
C6 L3
(option)
LNY-28
10pF disc 50pF var. 1µH
1µH
n/u
.001µF smt 1µH choke
LNY-50
10pF disc 50pF var. 0.33µH
0.33µH
n/u
68pF smt
1µH choke
LNY-100
6pF disc
11pF var. 0.22µH
0.22µH
n/u
68pF smt
0.33µH choke
LNY-120
4.5pF var. 11pF var. 6T #20 bus on ¼-20 screw form 0.33µH
n/u
.001µF smt 0.33µH choke
LNY-137
4.5pF var. 11pF var. 5T #20 bus on ¼-20 screw form 0.33µH
n/u
.001µF smt 0.33µH choke
LNY-146
4.5pF var. 11pF var. 5T #20 bus on ¼-20 screw form 0.33µH
n/u
.001µF smt 0.33µH choke
LNY-166
4.5pF var. 11pF var. 4T #20 bus on ¼-20 screw form 0.33µH
n/u
.001µF smt 0.33µH choke
LNY-220
4.5pF var 11pF var. 5T #20 bus on 8-18 screw form 0.33µH
n/u
.001µF smt 0.33µH choke
LNY-400
4.5pF var 4.5pF var 3T #20 bus 6-19 screw form
3T #20 bus 6-19 screw form
4.5pF var
4.5pF var
0.33µH choke
LNY-450
4.5pF var 4.5pF var 2T #20 bus 6-19 screw form
2T #20 bus 6-19 screw form
4.5pF var
4.5pF var
0.33µH choke
