Ramsey Electronics LPY915 User Manual

THE ‘LOGI’
LOG PERIODIC
ANTENNA

Ramsey Electronics Model No. LPY915

Constructed on rugged FR-4 material, it requires no tuning and
has no fragile antenna elements to break or twist! Covers the
entire 900 to over 2,500 MHz frequency range.
Why settle for any old antenna… this little baby “compresses”
the signal into a powerful beam that is 4 times more powerful in
the direction you desire!

• Easy hookup to your Receiver or Transmitter

• Small thin size with excellent broadband performance

• Solid 6 dB gain from 900 to over 2,000 MHz!

• VSWR less than 2:1 - great for transmitters up to 10 Watts!

• Easily mounted by itself or makes a great feed for reflector

dishes

• Construction ideas for a wideband corner reflector and a
‘grid’ reflector dish are covered in the manual!

• Very directional - ideal for point-to-point links

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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 Electrocardiogram Heart Monitor

• LC1 Inductance-Capacitance Meter

RAMSEY AMATEUR RADIO KITS

• DDF1 Doppler Direction Finder

• 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.

LPY915 INSTRUCTION MANUAL

Ramsey Electronics publication No. MLPY2 Rev 1.1

First printing: December 2001

COPYRIGHT 2001 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.

LPY2 • 2

Ramsey Publication No. MLPY915

Price $5.00

KIT ASSEMBLY

AND INSTRUCTION MANUAL FOR

Logi

LOG PERIODIC

ANTENNA

TABLE OF CONTENTS

Introduction .................................4

Antenna Description ...................4

Standard Hook-up ......................5

Low Frequency Modification ....... 7

Building a Corner Reflector ......... 7

Building a Reflector Grid ............. 9

LPY915 Return Loss Plot ...........10

Return Loss vs. VSWR Chart .....10

Warranty ..................................... 11

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RAMSEY ELECTRONICS, INC.

590 Fishers Station Drive

Victor, New York 14564

Phone [phone]

Fax [phone]

www.ramseykits.com

INTRODUCTION

This small log periodic antenna, which we call the ‘Logi’, is ideal for getting the
maximum performance out of any UHF to low frequency microwave wireless
system. Its directional properties “compresses” the signal into a powerful beam
that is 4 times more powerful in the desired direction. It is the ideal antenna for
scanners, wireless LANs, and other wireless devices. Its directional properties
make it exceptionally well suited for point-to-point links! The units small size
and wide bandwidth also make it ideal for feeding reflector antennas, such as
the easily constructed corner reflector or grid that are discussed later in the
manual.

ANTENNA DESCRIPTION

To start with, what is a log periodic antenna? The seeming simplicity of the log
periodic antenna belies the remarkable features of the design. It uses a
common transmission line to alternately feed a group of 1/4 λ dipoles that are
strung together. These antennas together display excellent radiation qualities
over a wide range of frequencies as well as relatively uniform input impedances
and good VSWR characteristics. While the log periodic design has been
around since the late 1950’s it has now been discovered to be at the cutting
edge of antenna development.

Looking at the physical layout of a
log periodic antenna, one would see
that it is comprised of multiple
elements working together to provide
a wide bandwidth of usable
frequencies. The active (radiating or
receiving radiation) portion of the

Feed
Point

antenna effectively shifts with
frequency as one stage becomes
‘more resonant’ than the next. The
lowest operating frequency is
determined by the longest element
and the highest operating frequency
is set by the shortest element. As the frequency of the transmission (or
reception) increases, the active region of the antenna shifts forward to the
shorter 1/4 λ dipole elements or vice versa as the frequency decreases.
Obviously then the ‘secret’ for proper operation must lie in the length and
spacing of the antenna elements. These and other factors must be carefully
chosen to cover the desired frequency range for the antennas’ application.
Instead of forcing you to figure out all the math and spend hours experimenting,
the creation of the Logi antenna (for frequencies between 900 and 2600 MHz)
comes to the rescue!

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