Ramsey Electronics LPA1 Instruction Manual

POWER BOOSTER

AMPLIFIER

Ramsey Electronics Model No. LPA1

Looking to boost the output of a small transmitter or signal
generator? Look no further. Our general purpose broadband
power amplifier is ideal for the test bench as well as any ham
radio applications. Get up to 1 watt RF power output!

• State of the art “MMIC” amplifier technology ensures great

quality amplification.

• The perfect lab amplifier for any lab bench! Excellent

bandwidth and gain characteristics make the LPA1 a useful tool
for amateurs and professionals alike.

• Boost almost any low power transmitter, up to 10mW maximum

input, from 300Khz to 1Ghz with up to one watt of power.

• Specially engineered PC board makes building a snap!

• No maintenance operation makes the LPA1 perfect for hassle

free operation.

• Amplification at up to 7,000 times the input power at 10Mhz!

• Perfect for boosting your QRP transmitter. Works on all bands

from 160 meters to the 1Ghz band!

LPA1 • 2

RAMSEY TRANSMITTER KITS

• FM100B Professional FM Stereo Transmitter

• FM25B Synthesized Stereo FM Transmitter

• MR6 Model Rocket Tracking Transmitter

• TV6 Television Transmitter

RAMSEY RECEIVER KITS

• FR1 FM Broadcast Receiver

• AR1 Aircraft Band Receiver

• SR2 Shortwave Receiver

• SC1 Shortwave Converter

RAMSEY HOBBY KITS

• SG7 Personal Speed Radar

• SS70A Speech Scrambler

• BS1 “Bullshooter” Digital Voice Storage Unit

• AVS10 Automatic Sequential Video Switcher

• WCT20 Cable Wizard Cable Tracer

• LABC1 Lead Acid Battery Charger

• ECG1 Heart Monitor

RAMSEY AMATEUR RADIO KITS

• HR Series HF All Mode Receivers

• QRP Series HF CW Transmitters

• CW7 CW Keyer

• CPO3 Code Practice Oscillator

• QRP Power Amplifiers

RAMSEY MINI-KITS
Many other kits are available for hobby, school, Scouts and just plain FUN. New
kits are always under development. Write or call for our free Ramsey catalog.

LPA1 POWER BOOSTER AMPLIFIER KIT INSTRUCTION MANUAL

Ramsey Electronics publication No. MLPA1 Revision 1.7a

First printing: April 2003

COPYRIGHT 1994 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York

14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.

LPA1 • 3

LPA1 POWER

BOOSTER AMPLIFIER

Ramsey Publication No. MLPA1

Price $5.00

TABLE OF CONTENTS

Introduction to the LPA1 ................... 4

How It Works .................................... 4

LPA1 Parts List ................................. 7

Schematic Diagram .......................... 8

Parts Layout Diagram ....................... 9

Feedback Circuit Considerations .... 10

LPA1 Assembly Instructions ............ 11

Setup and Testing ........................... 16

Troubleshooting ............................... 17

Ramsey Kit Warranty ...................... .19

KIT ASSEMBLY

AND INSTRUCTION MANUAL FOR

LPA1 • 4

Welcome to the LPA Power Booster Amplifier

Thank you for purchasing the LPA1 Power Booster Amplifier. The LPA -1 is
a state of the art amplifier for almost any low power transmitter. With a fre­quency range from 100Khz to almost 1Ghz, it is no wonder that it is so ver­satile. And with an incredible gain of up to 38.5dB (7079 times the input
power) at 10 Mhz, you can finally be heard over all of the noise and interfer­ence on many bands. For very low power ham radio QRP equipment, VCR
“rabbits,” and virtually anything else that you can hook it to, you will notice a
big difference in the signal distance and clarity. A gain of 38.5dB means that
only 125 micro watts will get you 1 watt of crystal clear power!

You’ll notice that the PC board included with your kit contains plating on both
sides of the board. This topside ground “plane” is necessary to create the
proper RF impedance in the traces run on the bottom side of the board. We
have also used the latest in trouble free amplifiers, the Mini Circuits MAV3
IC, to provide crystal clear linear amplification.

NOTE TO NEWCOMERS: If you are a first time kit builder, you may find this
manual easier to understand than you may have expected. Each part in the
kit is checked off as you go, while a detailed description of each part is given.
If you are to follow each step in the manual in order, and practice good sol­dering and kit building skills, the kit is next to fail-safe.

Circuit description

Your Power Booster Amplifier consists of a simple circuit in terms of compo­nents. Since the kit operates at frequencies as high as 1Ghz, your board has
been specially engineered for proper impedance matching. As signals go up
in frequency, they behave very differently than you might expect. Without a
properly designed board, the signal may actually begin to reflect throughout
the circuit. These reflections may cause a substantial loss of gain in the cir­cuit. To help eliminate this effect, your board has been designed using a
process called micro-strip design. This feature is what allows you to get rela­tively high gain from your LPA1 at very high frequencies. Throughout the
construction of this kit, it is extremely important to make sure that all leads on
components are kept as short as possible. If you do not make an attempt to
make the leads as short as possible, you may not find the output power or
gain as we have designed it.

The main components of the circuit are the RF amplifier and Q2, an MRF581
power transistor. The MAV3 is a state of the art amplifier specially designed
to work in a wide range of radio frequencies. The MAV3 amplifies the signal,
but does not have the power output capabilities to push out such high power.
For this reason, Q2 is placed in the circuit. Q2 amplifies the signal a bit more,
and is capable of generating a large amount of power out of the circuit.

LPA1 • 5

There are three other parts of this circuit. One simply turns on and supplies
power to the circuit. The second, supplies power to the MAV3 amplifier. The
third biases Q2 for proper operation.

Ramsey “Learn-as-you-build” Power Booster Assembly Strategy

Since the LPA1 runs at very high frequencies, it is extremely important that
you follow the instructions provided. Incorrectly installed components, exces­sively long component leads, and bad solder joints may mean that your kit
won’t work. For reasons like this it is advisable to follow the step-by-step in­structions in the manual and not jump ahead.

Be sure to read through all of the steps, and check the boxes as you go along
to be sure that you didn't miss any important steps. Before you switch on the
power in a hurry to see results, check all transistors, the MAV3 amplifier, D1
and C3 for proper orientation. Also check the board for any possible solder
shorts, or cold solder joints. All of these mistakes could have detrimental ef­fects on your kit - not to mention your ego!

Throughout the construction of the kit, we will try to explain the various com­ponents and their function in the circuit. Who ever said that you can’t learn
something while you are having fun? If your kit has problems, we have also
included a step by step troubleshooting section to guide you through them.
Please remember that most problems occur out of bad soldering technique
and improperly placed components. A clear head and a meter are all that you
probably need to solve the problem. Since it is virtually impossible for our
technicians to “troubleshoot” step by step over the phone, please follow the
troubleshooting guide provided in your manual.

Kit building tips:

Use a good soldering technique - let your soldering iron tip gently heat both
the wires and pads simultaneously. Apply the solder to the wire and the pad
when the pad is hot enough to melt the solder. The finished joint should look
like a drop of water on paper, somewhat soaked in. If the pads have not
heated up sufficiently, melted solder (heated by the iron itself) will form a cold
solder joint and will not conduct. These appear to be dull beads of solder, and
can be fixed easily be applying heat to the pad and wire. Mount all parts on
the top side of the board. This is the side with no traces or pads.

Part installation - when parts are installed, the part is placed flat to the board,
and the leads are bent on the backside of the board to prevent the part from
falling out before soldering. The part is then soldered securely to the board,
and the remaining lead length is clipped off. Please keep in mind that it is ex­tremely vital to place the parts as close to the board as possible. This is nec­essary for proper operation over the wide frequency range of the amplifier.

LPA1 • 6

Double sided component soldering instructions:

You’ll notice that the circuit board contains plating on both sides of the board,
with a large ground “plane” area on the component side of the circuit board.
In order to electrically connect this topside ground plane to the bottom side
ground connections, it will be necessary to solder some connections on both
the top and bottom sides of the circuit board.

These topside connections will be clearly pointed out when necessary in the
assembly instructions. When so instructed, be sure the solder “flows” around
the topside connection, as shown. When installing a disc capacitor, be sure
to scrape away any insulating material which may be coated on the lead near
the components’ body. Also, be aware that for every part that you solder on
the top side of the board, there should also be a connection on the bottom
side for that same lead.

Another important consideration when building high frequency RF circuits is
to keep the component lead lengths as short as mechanically possible to
keep the components close to the PC board. This will avoid adding stray ca­pacitance or inductance into the circuit.

5

Component
(Disc Cap shown)

Topside solder
connection

"Normal" bottomside
connection