• 16 db Gain, 1 db Noise Figure
• Runs on 9 to 15 VDC
• Hi-Q tuned input to reduce
overload
• Small size to fit in any rig
• The most popular preamp kit in
the USA!
220 MHz
LOW NOISE
PREAMP
• Easy 15 minute assembly
Perk up your reception on 220 MHz with this easy-to-build and install kit.
Works well with any radio - especially effective in repeaters. Rugged design
using a microwave transistor outperforms units costing triple the price!
Kit No. PR20
PR20—1
KIT
INTRODUCTION TO THE PR20 LOW NOISE PREAMPLIFIER
A “preamplifier” gives an initial boost, measured in decibels, to the level of a signal before it
is further processed by tuned circuits, filters, amplifiers, mixers, detectors, or other circuit
stages. Preamps may be designed for either RF or audio use and may be either tuned or
broadbanded.
The Ramsey Low Noise PR10, 20, and 40 Preamplifiers for 144, 220, and 440 MHz,
respectively, differ from our popular SA7 and PR2 broadband preamplifiers in that these
models include high-Q tuned input circuits to pre-select the desired frequency range,
restricting the strength of other out-of-band signals. Also, the microwave transistor is biased
for best low noise performance.
PR20—2
CIRCUIT DESCRIPTION
L1 and C2 form a tuned input filter for the preamp to reject out-of-band signals. The 3 db
bandwidth of this filter is 6MHz. L1 is adjustable for peak performance. The 2SC2498
transistor is a bipolar silicon NPN low noise UHF/VHF amplifier in a TO-92 case suitable for
service up to 5 GHz, with maximum device dissipation of 600 milliwatts. Q1 has a very low
noise figure, determined by the bias established by R1 and R2. The actual circuit is about
as simple as they come. Maximum gain and freedom from oscillation are accomplished by
the quality of workmanship in parts installation and I/O connector wiring
PR20—3
PARTS SUPPLIED WITH PR20 KIT
CAPACITORS
2 2 or 2.2pF disc capacitor (C1,2)
1 10pF disc capacitor (C3)
1 100pF disc capacitor [marked 100 or 101] (C4)
1 .01uF disc capacitor [may be marked .01, 103, or 10nF] (C5)
RESISTORS
1 470 ohm [yellow-violet-brown] (R1)
1 100K ohm [brown-black-yellow] (R2)
OTHER COMPONENTS
1 PRX printed circuit board
1 shielded adjustable coil (L1) [marked 359-7787]
1 2SC2498 or 2570 microwave bipolar transistor (Q1)
REQUIRED, NOT SUPPLIED
9 - 15 VDC power source
RF input and output connectors (your choice of type)
PR20—4
RAMSEY PR20 PRE-AMP PARTS LAYOUT
*
NOTE FOR PR-20:
Disregard C6
PR20—5
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