Had requests for the 160m preamp I mentioned in previous post. Here it is:
L M N
|-------| |----|--|-I-|-| |-S
A----|---|---| |---|----|--|---I-----|---->| --- | | | Q R
B C D E F G H J K |--|V W^---O-| | F | |
| | | | | | | | | | Y | X X
X X X X X X X X T U | X
| | I--Z
X X |
X
X = Ground
A is the input from beverage antenna (direct or via coax)
B Connect 1N4006 diode to ground, cathode grounded
C " " " " " , anode "
D and E are the input matching transfomer, T1, wound on T-68-1 core.
D is 7 turns over the cold end of E, which is 39 turns no. 24 enamel.
F is 0-700 pf variable capacitor
G is 1N914 diode, cathode grounded
H " " " anode "
I is .001 mf ceramic disc capacitor
J is 220K 1/2 watt resistor
K is the Gate of Q1, an MPF102. L is the Drain and V is the Source.
M is the Source of Q2, an MPF102. N is the Drain, W is the Gate.
O is a 27K 1/2 watt resistor, connected from teh Drain to the Gate of Q2.
Q and R are the output matching transformer, T2. Same as T1 but Q is the 39
turn side, R is 7 turns.
S is the coax output to the receiver
T is 0-200 ohm potentiometer for gain control.
U is a 6800 ohm resistor from the Gate of Q2 to ground. Also connect a .001
mf ceramic disc capacitor from the Gate of Q2 to ground.
Y is 2.5 mh RFC
Z is 9-12 VDC + power source. If you just use a battery, you can eliminate
the RFC.
Values are not critical. The back-to-back diodes are for protection from
lightning or transmitter-induced surges. Radio Shack stocks MPF102's for
around 79 cents. (I have no vested interest in Radio Shack. There are
cheaper mail-order sources).
I have used versions of this preamp in the shack as well as at the feedpoint
of beverage antennas.
If this is too hard to decipher, send me an SASE and I'll send you
a copy of the schematic. June '78 page 55 of 73 Magazine had a version. 1974
(I think) ARRL Handbook had an 80-10m version. Versions of it have appeared
in QST and CQ over the years.
73/Jon AA1K
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