Ramsey Electronics AA7 User Manual

ALL BAND HF, VHF, UHF

ACTIVE ANTENNA

Ramsey Electronics Model No. AA7

Stuck for antenna space? Don’t want to string any more wires?
This ACTIVE ANTENNA KIT gives you roof-top performance on
a desk top!

• Great for perking up scanner reception.

• Dual preamp HF-VHF/UHF front panel switching.

• Circuit based on true active antenna research.

• Performance rivals units costing many times more!

• Front panel RF gain control.

• Uses Dual Gate MOSFET technology for low noise HF amplification,

and a high gain microwave transistor for VHF/UHF.

• Includes internal telescopic whip antenna plus auxiliary antenna

input jack for jazzing up existing antennas.

• Clear, concise assembly instructions carefully guide you to a

finished kit that works FIRST time!

• Informative manual answers questions on theory, hookups and

uses - enhances resale value, too!

• Ideal companion to any Ramsey receiver.

• Power switch cuts the AA7 active antenna in and out of the antenna

line with no need to change cables.

• Runs on a standard 9 volt battery!

AA7 • 1

PARTIAL LIST OF AVAILABLE KITS
RAMSEY TRANSMITTER KITS

• FM10, FM25B FM Stereo Transmitters

• FM100 Super Pro FM Transmitter

• MR6 Model Rocket Tracking Transmitter

• AM1, AM25 AM Transmitters

RAMSEY RECEIVER KITS

• FR1 FM Broadcast Receiver

• AR1 Aircraft Band Receiver

• SR2 Shortwave Receiver

• HFRC 10 MHz WWV Receiver

• SC1 Shortwave Converter

RAMSEY HOBBY KITS

• SG7 Personal Speed Radar

• SS70A Speech Scrambler

•TG1 DTMF Tone Grabber

• BS1 “Bullshooter” Digital Voice Storage Unit

• AVS10 Automatic Sequential Video Switcher

• WCT20 Cable Wizard Cable Tracer

• MD3 Microwave Motion Detector

• ML Music Lights Kit

• LC1 Inductance-Capacitance Meter

RAMSEY AMATEUR RADIO KITS

• HR Series HF All Mode Receivers

• QRP Series HF CW Transmitters

• CW7 CW Keyer

• 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.

AA7 ACTIVE ANTENNA KIT INSTRUCTION MANUAL

Ramsey Electronics publication No. MAA7 Revision E

First printing: August, 1994

COPYRIGHT

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.



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

AA7 • 2

Ramsey Publication No. MAA7

Manual Price Only: $5.00

KIT ASSEMBLY

AND INSTRUCTION MANUAL FOR

AA7 ACTIVE

ANTENNA KIT

TABLE OF CONTENTS

Introduction to the AA7 ............................................. 4

Circuit and Device Description .................................. 4

Active Antennas: Circuits With a Purpose ................ 5

Parts List ................................................................... 6

Assembly Instructions ............................................... 7

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

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

Initial Tests ................................................................ 12

Using your AA7 ......................................................... 12

Troubleshooting Guide ............................................. 13

Active Antenna Comparisons ................................... 14

The AA7’s Enclosure ................................................ 14

A Final Suggestion .................................................... 14

Ramsey Kit Warranty ................................................ 15

AA7 • 3

RAMSEY ELECTRONICS, INC.

590 Fishers Station Drive

Victor, New York 14564

Phone [phone]

Fax [phone]

INTRODUCTION TO THE AA7

We believe that you will discover and agree with us that your new AA7 is
the best VALUE in a true receiver antenna. In its simplest form, an “active
antenna” is a small antenna going through an RF preamplifier to a receiver.
Generally, the actual antenna may be of several different styles:

• broad-band (no tuning required)

• fixed-tuned (i.e., pre-set for a specific frequency)

• variable-tuning (permits peaking or “pre-selecting” a variety of band

choices)

It is easy to assume that the “ideal” active antenna would peak your
desired signal or frequency band. Several excellent active antennas are
available for this purpose in the $75 - $150 price range, but we would point
out that using this kit plus an additional $1 in mini coax to approximate your
antenna will work as well, or even better. In our humble opinion, if you really
want to spend that much money, you’re better off spending an extra five
dollars and buying a good quality receiver. (Study the Ramsey HR-series or
our SR-1 shortwave receiver, and you will see how easy that idea can really
be!)
If what you want is a great quality active antenna for a whole lot less than
others sell it for, the answer is obvious. The Ramsey AA7 active antenna.

An active antenna is a compromise between what is ideal... and what is
real. Real antennas are wire or tubing properly measured in meters, not
transistors or variable capacitors. If you find yourself in a difficult antenna
situation for casual listening or monitoring, we think that you’ll get more
satisfaction from understanding and using your AA7 than from wishing that
you spent your money on a tunable model would result in a real antenna!

CIRCUIT AND DEVICE DESCRIPTION

The AA7 features two independent, switchable RF preamplifiers. The HF
(high frequency) section is located on the upper middle section of the
schematic on page 6, while the VHF (Very High Frequency) / UHF (Ultra
High Frequency) section is located on the lower middle section.

Simple switching circuits play a major role in the practical use of the AA7.
S2:B connects the RF input and output connectors in the “power off”
position. This gives the receiver non-amplified access to the auxiliary
antenna jack, as well as the on-board rod antenna. With S2 in its “power on”
position, S1 selects between the two independent antenna amplifier
configurations (HF or VHF).

AA7 • 4

The dual-gate MOSFET amplifier circuit (Q1), selected with S1 in the “out”
position is designated the HF preamp circuit, due to the exceptionally low
noise level of its operation. This is ideal for enhancing weak CW-SSB
signals. This amplifier performs the true “active antenna” function of the
AA7.

The 2SC2498 amplifier circuit (Q2), selected with S1 in the “in” position, is
designated the VHF preamp circuit, due to the excellent VHF (very high
frequency) and microwave (baked-potato frequency) response
characteristics of the 2SC2498. With the on-board whip antenna adjustable
for peak resonance throughout the VHF- UHF region (Wavelength [ft.] = 234/
f [MHz] - terribly long for a baked potato), this mode of the AA7 is ideal for
indoor, outdoor and portable use of VHF scanners and other receivers.

Both modes are usable for HF, while the 2SC2498 offers higher gain but
also a higher noise level. The user can easily choose either amplifier for
copying any signal of interest. The front panel gain control (R5) is usable
with either amplifier.

ACTIVE ANTENNAS: CIRCUITRY WITH A PURPOSE:

There is more to a true active antenna than any old preamp or preselector
hooked to a piece of wire.

The AA7 was designed with reference to research carried out by Ulrich L.
Rohde and T.T.N. Bucher, who co-authored Communications Receivers:
Principals and Design (New York: McGraw-Hill Book Company). Rohde also
shares credit for the highly sophisticated Rohde-Schwarz Type HE010
10KHz-80MHz Active Antenna. The book illustrates how proper design of a
broadband active antenna can give receiver performance very comparable to
a quarter-wave vertical ("passive antenna") for a given frequency. The
book's footnotes cite considerable study by professionals on the optimum
design of active antennas.

A short rod antenna, such as the whip supplied with your AA7, "receives"
signals from the whole radio spectrum. Hence if you were to connect it
directly to the antenna connection of your HF SWL receiver or antenna
connection, you may not be impressed. The reason is not so much that the
antenna is too short, or not resonant, but that its performance is all but
shorted-out by the receiver, which is “looking for” a more conventional
antenna.

A well-designed broadband active antenna considers field strength of the
desired signal (measured in microvolts per meter of antenna length),
atmospheric and other noise, diameter of the antenna, radiation resistance
and antenna reactance at various frequencies, plus the efficiency and noise

AA7 • 5