DESIGN AND CONSTRUCTION OF AN HF/VHF/UHF 3-3000MHz ACTIVE ANTENNA

NAME/INDEX

SUBMITTED IN PARTIAL FULFILMENT FOR THE AWARD OF HIGHER NATIONAL DIPLOMA IN ELECTRICAL/ELECTRONICS

ENGINEERING

DEPARTMENT OF ELECRICAL/ELECTRONICS ENGINEERING ACCRA POLYTECHNIC

SEPTEMBER 2008

CERTIFICATION BY SUPERVISOR

I hereby certify that this project work was carried out under my

supervision. I therefore approve that the work is adequate in scope

and quality for the partial fulfillment of the requirement for the award

of a Higher National Diploma (HND) in Electrical/Electronics

Engineering.

SUPERVISOR:

SIGN…………………………….

DATE……………………………

I

DEDICATION

This project is dedicated to

II

DECLARATION

I ………………………………………………….. Declares that the work

was undertaken whilst in Accra Polytechnic.

I further affirm that, this work so far as I know has not been

submitted to any institution for the award of any certificate and the

source of information has been fully acknowledged

NAME………………………………………..

SIGN…………………………….

DATE……………………………

III

ACKNOWLEDGEMENT

IV

ABSTRACT

The project in question is an Active Antenna which is used to

amplify radio signals received by a passive antenna.

When connected to a passive antenna with resistance ranging from

75 to 300Ω the active antenna boosts the signals to a higher and

strong signal to be fed to a television or a radio receiver.

The Active Antenna amplifies signals with frequencies between 3 to

3000MHz.

V

TABLE OF CONTENTS

CONTENT PAGE

CHAPTER ONE

1.1 INTRODUCTION 1

1.2 BACKGROUND 2

1.3 DEFINATION 3

1.4 OBJECTIVES 4

1.5 SIGNIFICANCE OF STUDY 5

1.6 METHOLOGY 6

CHAPTER TWO

2.1

VI

CHAPTER THREE

3.1 COMPONENT LIST

3.2 CABLE

CHAPTER FOUR

4.1 GENERAL MODE OF OPERATION

4.2 IMPORTANT

4.3 PRECAUTIONS

4.4 SUMMARY

4.5 RECORMENDATIONS

REFERNCE

VII

CHAPTER ONE

1.1 INTRODUCTION

If you have a shortwave or high-frequency receiver or scanner that

is struggling to capture signals with a short, whip antenna, and you'd

like the kind of performance that a 60-foot long wire antenna can

provide but lack the space to put one up, consider using the AA-7 HF/VHF/UHF Active Antenna described in this article. The AA-7 is

a relatively simple antenna that is designed to amplify signals from 3

to 3000 Megahertz, including three recognized ranges: 3-30 MHz

high-frequency (HF) signals; 3-300 MHz very-high frequency (VHF)

signals; 300-3000MHz ultra-high (UHF) frequency signals. Those

bands are typically occupied by shortwave, television stations,

government, and commercial radio signals.

1

1.2 BACKGROUND

In many of our urban cities it is rear to see people mounting tall

poles to fix an antenna. They may want to but are reluctant because

of the amount of work they’ll have to do before receiving a signal

from a radio of television station which is only a few kilometers from

them.

How much more someone in a distant place, say in about hundreds

of miles away from that station. No wonder there are a lot of tall

bamboo pole in this remote places.

It is to this effect that this project was designed to amplifier the little

signals received by the existing passive antennas.

2

1.3 DEFINITION

The project 3-3000MHz active antenna is named AA7 as

abbreviation of Active Antenna and the seven stands for the variety

of frequencies.

It can be powered by a 9v small size battery when used outdoors or

a place where there’s no electricity or powered by the mains.

It is convenient to carry and portable.

Also comes with easy to connect terminals and a gain control.

3

1.4 OBJECTIVES

The main objective of this project is to help increase weak signals

received by radio devices and amplify them into strong and better

signals.

Another objective is to create alternative power for it to make is easy

to use at places where there’s no electricity.

The project is also designed aid people at places where transmitted

signals between 3-3000 MHz received have strength or weak. It is

our aim that every person irrespective of their location to enjoy good

reception of radio and TV transmission.

4

1.5 SIGNIFICANCE OF STUDY

The main objective of this project is

To help increase our knowledge of study on the existing Active

antennas and to improve on them.

To replace the existing ones with a more accessible and user

friendly type.

To help prevent the hazards of tuning you antenna every time

one changes the TV or Radio channel.

This project is versatile making it easy to be applied either a

Television or radio set.

To make an active antenna that is transferable and applicable

any where.

5

1.6 METHODOLOGY

In its simplest form, an active antenna uses a small whip antenna

that feeds incoming RF to a pre-amplifier, whose output is then

connected to the antenna input of a receiver. Unless specifically

designed otherwise, all active antennas are intended for receive-

only operation, and thus should not be used with transceivers;

transmitting into an active antenna will probably destroy its active

components. A well designed broadband active antenna consider

field strength of the desired signal (measured in micro volts 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 figure of the amplifier

circuit itself.

All important information needed for this project to takeoff was

acquired form two main source namely primary and secondary

sources.

Primary source were sources were the personal interactions with my

supervisor and workers of a well equipped and well knowledgeable

on this project.

Secondary sources were the research at the library and the internet.

6

CHAPTER TWO2.1 Terminology

The words antenna (plural: antennas[) and "aerial" are used

interchangeably; but usually a rigid metallic structure is termed an

antenna and a wire format is called an aerial. In the United Kingdom

and other British English speaking areas the term aerial is more

common, even for rigid types. The noun aerial is occasionally written

with a diaresis mark — aërial — in recognition of the original spelling

of the adjective aërial from which the noun is derived.

The origin of the word antenna relative to wireless apparatus is

attributed to Guglielmo Marconi. In 1895, while testing early radio

apparatus in the Swiss Alps at Salvan, Switzerland in the Mont

Blanc region, Marconi experimented with early wireless equipment.

A 2.5 meter long pole, along which was carried a wire, was used as

a radiating and receiving aerial element. In Italian a tent pole is

known as l'antenna centrale, and the pole with a wire alongside it

used as an aerial was simply called l'antenna. Until then wireless

radiating transmitting and receiving elements were known simply as

aerials or terminals. Marconi's use of the word antenna (Italian for

pole) would become a popular term for what today is uniformly

known as the antenna.

7

A Hertzian antenna is a set of terminals that does not require the

presence of a ground for its operation (versus a Tesla antenna

which is grounded.) A loaded antenna is an active antenna having

an elongated portion of appreciable electrical length and having

additional inductance or capacitance directly in series or shunt with

the elongated portion so as to modify the standing wave pattern

existing along the portion or to change the effective electrical length

of the portion. An antenna grounding structure is a structure for

establishing a reference potential level for operating the active

antenna. It can be any structure closely associated with (or acting

as) the ground which is connected to the terminal of the signal

receiver or source opposing the active antenna terminal, (i.e., the

signal receiver or source is interposed between the active antenna

and this structure.

2.2 OverviewAntennas have practical uses for the transmission and reception of

radio frequency signals (radio, TV, etc.). In air, those signals travel

close to the speed of light in vacuum and with a very low

transmission loss. The signals are absorbed when propagating

through more conducting materials, such as concrete walls, rock,

etc. When encountering an interface, the waves are partially

reflected and partially transmitted through.

8

2.3 ParametersThere are several critical parameters that affect an antenna's

performance and can be adjusted during the design process. These

are resonant frequency, impedance, gain, aperture or radiation

pattern, polarization, efficiency and bandwidth. Transmit antennas

may also have a maximum power rating, and receive antennas differ

in their noise rejection properties. All of these parameters can be

measured through various means.

2.4 Resonant frequency

The "resonant frequency" and "electrical resonance" is related to the

electrical length of the antenna. The electrical length is usually the

physical length of the wire divided by its velocity factor (the ratio of

the speed of wave propagation in the wire to c0, the speed of light in

a vacuum). Typically an antenna is tuned for a specific frequency,

and is effective for a range of frequencies usually centered on that

resonant frequency. However, the other properties of the antenna

(especially radiation pattern and impedance) change with frequency,

so the antenna's resonant frequency may merely be close to the

center frequency of these other more important properties.

9

Antennas can be made resonant on harmonic frequencies with

lengths that are fractions of the target wavelength. Some antenna

designs have multiple resonant frequencies, and some are relatively

effective over a very broad range of frequencies. The most

commonly known type of wide band aerial is the logarithmic or log

periodic, but its gain is usually much lower than that of a specific or

narrower band aerial.

2.5 Gain

Gain as a parameter measures the directionality of a given antenna.

An antenna with a low gain emits radiation with about the same

power in all directions, whereas a high-gain antenna will

preferentially radiate in particular directions. Specifically, the Gain,

Directive gain or Power gain of an antenna is defined as the ratio

of the intensity (power per unit surface) radiated by the antenna in a

given direction at an arbitrary distance divided by the intensity

radiated at the same distance by an hypothetical isotropic antenna.

The gain of an antenna is a passive phenomenon - power is not

added by the antenna, but simply redistributed to provide more

radiated power in a certain direction than would be transmitted by an

isotropic antenna. If an antenna has a greater than one gain in some

directions, it must have a less than one gain in other directions since

energy is conserved by the antenna.

10

An antenna designer must take into account the application for the

antenna when determining the gain. High-gain antennas have the

advantage of longer range and better signal quality, but must be

aimed carefully in a particular direction. Low-gain antennas have

shorter range, but the orientation of the antenna is inconsequential.

For example, a dish antenna on a spacecraft is a high-gain device

(must be pointed at the planet to be effective), while a typical WiFi

antenna in a laptop computer is low-gain (as long as the base

station is within range, the antenna can be in an any orientation in

space). It makes sense to improve horizontal range at the expense

of reception above or below the antenna. Thus most antennas

labeled "omnidirectional" really have some gain Sometimes, the

half-wave dipole is taken as a reference instead of the isotropic

radiator. The gain is then given in dBd (decibels over dipole):

0 dBd = 2.15 dBi

2.6 Radiation pattern

The radiation pattern of an antenna is the geometric pattern of the

relative field strengths of the field emitted by the antenna. For the

ideal isotropic antenna, this would be a sphere. For a typical dipole,

this would be a toroid. The radiation pattern of an antenna is

typically represented by a three dimensional graph, or polar plots of

the horizontal and vertical cross sections.

11

2.7 Impedance

As an electro-magnetic wave travels through the different parts of

the antenna system (radio, feed line, antenna, free space) it may

encounter differences in impedance (E/H, V/I, etc). At each

interface, depending on the impedance match, some fraction of the

wave's energy will reflect back to the source[5], forming a standing

wave in the feed line. The ratio of maximum power to minimum

power in the wave can be measured and is called the standing wave

ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to

be marginally acceptable in low power applications where power

loss is more critical, although an SWR as high as 6:1 may still be

usable with the right equipment. Minimizing impedance differences

at each interface (impedance matching) will reduce SWR and

maximize power transfer through each part of the antenna system.

Complex impedance of an antenna is related to the electrical length

of the antenna at the wavelength in use. The impedance of an

antenna can be matched to the feed line and radio by adjusting the

impedance of the feed line, using the feed line as an impedance

transformer. More commonly, the impedance is adjusted at the load

(see below) with an antenna tuner, a balun, a matching transformer,

matching networks composed of inductors and capacitors, or

matching sections such as the gamma match.

12

2.8 Bandwidth

The "bandwidth" of an antenna is the range of frequencies over

which it is effective, usually centered on the resonant frequency.

The bandwidth of an antenna may be increased by several

techniques, including using thicker wires, replacing wires with cages

to simulate a thicker wire, tapering antenna components (like in a

feed horn), and combining multiple antennas into a single assembly

and allowing the natural impedance to select the correct antenna.

Small antennas are usually preferred for convenience, but there is a

fundamental limit relating bandwidth, size and efficiency.

Polarization

The "polarization" of an antenna is the orientation of the electric field

(E-plane) of the radio wave with respect to the Earth's surface and is

determined by the physical structure of the antenna and by its

orientation. It has nothing in common with antenna directionality

terms: "horizontal", "vertical" and "circular". Thus, a simple straight

wire antenna will have one polarization when mounted vertically,

and a different polarization when mounted horizontally.

"Electromagnetic wave polarization filters" are structures which can

be employed to act directly on the electromagnetic wave to filter out

wave energy of an undesired polarization and to pass wave energy

of a desired polarization.

13

Reflections generally affect polarization. For radio waves the most

important reflector is the ionosphere - signals which reflect from it

will have their polarization changed unpredictably. For signals which

are reflected by the ionosphere, polarization cannot be relied upon.

For line-of-sight communications for which polarization can be relied

upon, it can make a large difference in signal quality to have the

transmitter and receiver using the same polarization; many tens of

dB difference are commonly seen and this is more than enough to

make the difference between reasonable communication and a

broken link.

Polarization is largely predictable from antenna construction but,

especially in directional antennas, the polarization of side lobes can

be quite different from that of the main propagation lobe. For radio

antennas, polarization corresponds to the orientation of the radiating

element in an antenna. A vertical omnidirectional WiFi antenna will

have vertical polarization (the most common type). An exception is a

class of elongated waveguide antennas in which vertically placed

antennas are horizontally polarized. Many commercial antennas are

marked as to the polarization of their emitted signals.

Polarization is the sum of the E-plane orientations over time

projected onto an imaginary plane perpendicular to the direction of

motion of the radio wave.

14

In the most general case, polarization is elliptical (the projection is

oblong),meaning that the antenna varies over time in the

polarization of the radio waves it is emitting. Two special cases are

linear polarization (the ellipse collapses into a line) and circular

polarization (in which the ellipse varies maximally). In linear

polarization the antenna compels the electric field of the emitted

radio wave to a particular orientation. Depending on the orientation

of the antenna mounting, the usual linear cases are horizontal and

vertical polarization. In circular polarization, the antenna

continuously varies the electric field of the radio wave through all

possible values of its orientation with regard to the Earth's surface.

Circular polarizations, like elliptical ones, are classified as right-hand

polarized or left-hand polarized using a "thumb in the direction of the

propagation" rule. Optical researchers use the same rule of thumb,

but pointing it in the direction of the emitter, not in the direction of

propagation, and so are opposite to radio engineers' use.

In practice, regardless of confusing terminology, it is important that

linearly polarized antennas be matched, lest the received signal

strength be greatly reduced. So horizontal should be used with

horizontal and vertical with vertical. Intermediate matchings will lose

some signal strength, but not as much as a complete mismatch.

15

Transmitters mounted on vehicles with large motional freedom

commonly use circularly polarized antennas so that there will never

be a complete mismatch with signals from other sources. In the case

of radar, this is often reflections from rain drops.

2.9 Transmission and reception

All of the antenna parameters are expressed in terms of a

transmission antenna, but are identically applicable to a receiving

antenna, due to reciprocity. Impedance, however, is not applied in

an obvious way; for impedance, the impedance at the load (where

the power is consumed) is most critical. For a transmitting antenna,

this is the antenna itself. For a receiving antenna, this is at the

(radio) receiver rather than at the antenna. Tuning is done by

adjusting the length of an electrically long linear antenna to alter the

electrical resonance of the antenna.

16

CHAPTER THREE

3.1 Active AntennasIn its simplest form, an active antenna uses a small whip antenna

that feeds incoming RF to a pre-amplifier, whose output is then

connected to the antenna input of a receiver. Unless specifically

designed otherwise, all active antennas are intended for receive-

only operation, and thus should not be used with transceivers;

transmitting into an active antenna will probably destroy its active

components. A well designed broadband active antenna consider

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 figure of the amplifier

circuit itself.

17

3.2 Circuit DescriptionThe schematic diagram of the AA-7, contains only two active

elements; Q1 (an MFE201 N-Channel dual-gate MOSFET) and Q2

(a 2SC2570 NPN VHF silicon transistor). Those transistors provide

the basis of two independent, switchable RF pre-amplifiers. Two

double-pole double-throw (DPDT) switches play a major role in this

operation of the AA-7. Switch S1 is used to select one of the two

pre-amplifier circuits (either HF or VHF/UHF). Switch 2 is used to

turn off the power to the circuit, while coupling the incoming RF

directly to the input of the receiver. That gives the receiver non-

amplified access to the auxiliary antenna jack, at J1, as well as the

on-board telescoping whip antenna. With switch S2 in its power-on

position, the input and output jacks are disconnected and B1 (a 9

volt battery) is connected to the circuit. With switch S1 in the

position shown in the schematic, incoming RF is directed to the HF

pre-amp circuit built around Q1 (an MFE201 N-Channel dual-gate

MOSFET). The HF pre-amp operates with an exceptionally low

noise level, and is ideal for copying weak CW and singe-side band

signals. When S1 is switched to the other position, the captured

signal is coupled to the VHF/UHF pre-amp built around Q2 (a

2SC2570 NPN VHF silicon transistor), which has excellent VHF

through microwave characteristics.

18

With the on-board whip antenna adjustable to resonance through

much of the VHF-UHF region (length in feet = 234 divide by the

frequency in MHz), the VHF/UHF mode is ideal for indoor and

portable use with VHF scanners and other receivers. Either mode

can be used when tuning 3-30 MHz HF signals. The VHF/UHF pre-

amp offers higher gain than the HF pre-amp, but also has a higher

noise level. You can easily choose either amplifier for copying any

signal; of interest--just try both positions. The RF gain control (R5)

can be used to trim the output of either amplifier.

Caution: The AA-7 is not intended for transmitting operation (be it

Ham, Maritime, or CB); if it is used with a transceiver of any kind,

make sure it is not possible to transmit by accidentally pressing a

mike button or CW key. Transmitting RF into the AA-7 is likely to

ruin one of both of the transistors in the circuit.

19

3.3 CIRCUIT CONSTRUCTIONThe AA-7, which can be built from scratch or purchased in kit

form from the supplier listed in the Parts List, was assembled on

a printed circuit board, measuring 4 by 4-11/16 inches. A

template for the PCB board is shown in fig. 2. You can either

etch your own board from that template, or purchase the circuit

board or the complete kit of parts (which includes the pcb and

all parts, but not the enclosure). The kit comes with a 16-page

kit instruction manual that gives step-by-step assembly

instructions and contains additional information not covered in

this article. Kit assembly time, working slowly and carefully,

should take less than an hour. Most of the parts specified in the

Parts list are standard components and can be procured

through conventional hobby electronics suppliers. However,

some parts--J1, J2, S1, S2, and R5-- have particular physical

mounting dimensions; the Printed Circuit Board is designed to

accept these particular parts. In addition, Q1 and Q2 can be

hard to find; however, it is possible to make substitutions

provided that you can find a supplier. Suitable replacements for

Q1 and Q2 are given in the Parts List.

The telescoping whips antenna screw-mounts to the board; the

screw provides contact between the printed circuit board traces

and the antenna.

20

To save time and trouble locating and ordering hard-to-find

parts, a Special Parts Kit is also offered by the supplier listed in

the Parts List.

A parts placement (layout) diagram for the AA-7's printed circuit

board is shown in figure 3. When assembling the circuit, be

especially careful that transistors Q1 and Q2, and the

electrolytic capacitor C4, are oriented as shown.

Although not shown in the schematic (Fig. 1) or the layout (Fig.

3) diagrams, an optional led power indicator can be added to

the circuit. Adding a power indicator to the circuit allows you to

tell at a glance if the circuit is on; leaving the circuit on, even

though the AA-7 draws only about 0.7 mA, will eventually

discharge the battery. Of course, adding an led will increase the

current drain to by about 7 mA, but the red glow makes it

obvious when the unit is on.

If you decide to include the LED indicator in your project, power

for the indicator can be easily taken from the switched 9-volt DC

terminal of S2 (center terminal, right side, looking at the top of

S2). Simply connect the positive voltage to the anode (longer

wire) of the led and connect her cathode lead through a current

limiting resistor of about 1000 ohm to a ground point on the

printed circuit board, or as the author did from the frame of R5.

Mount the led at any convenient point near the switch.

21

3.4 SCHEMATIC DIAGRAM

223.5 COMPONENT LIST

COMPONENT DESCRIPTION QUANTITY

Q1 AF239S (DUAL-GATE MOSFET) 1

Q2 2SC2570 (NPN VHF/UHF SILICON

TRANSISTOR)

1

R1 1MΩ (MEGA OHM RESISTOR) 1

R2 220KΩ (RESISTOR) 1

R3,R6 100KΩ (RESISTOR) 2

R4 100Ω (RESISTOR) 1

R5 10K Ω POTENTIOMETER 1

C1,C2,C5,C6 0.01uF, CERAMIC DISC 4

C3 100pF CERAMIC DISC 1

C4 4.7 to 10Uf/16VDC,

ELECTROLYTIC CAPACITOR

1

S1,S2 DPDT SWITCH 2

MISC PCB BOARD, WIRE, SOLDER

23

CHAPTER FOUR

4.1 GENERAL MODE OF OPERATIONThe RF preamplifier section of an active antenna may be of several

different styles. A fixed-tuned preamp has the greatest gain for the

specific frequency of the operation, but is limited to only that

frequency. A variable-turned amplifier can be peaked within a range

of frequencies, but the circuitry is more complex and expensive and

tuning requires constant resetting whenever the receiver frequency

is changed. A broadband preamplifier doesn’t require any tuning,

Making it very versatile and easy to use, but has less gain at any

specific frequency. The AA-7 described here. For simplicity and low

cost, is of a dual broadband design.

24

4.2 LIMITATIONS

The difficulties involved in getting the major component from a class

A source was very difficult because all the companies who

manufactures these components do not sell components in small

quantities and it was very hectic getting all these components.

Some of the components were imported from Singapore and that

took a lot of time to arrive making it difficult to compile study and the

construction of the project together.

Researches, typing and printing is very difficult to complete because

of the frequent power outages and time constrains.

25

4.3 PRECAUTIONS In other to arrive at a good and a successful project, the following

precautions were taken into consideration:

1. The circuit was built under supervision to ensure accuracy.

2. The circuit diagram was first tested with schematic circuit

stimulator software and then mounted on a Vero board and

then rechecked for accuracy to prevent damage of any

component.

3. The entire component were thoroughly checked and tested for

consistency and efficiency.

4. Correct soldering techniques were ensured as well as the

usage of a correct solder.

5. The right tools and equipment were used for this project.

6. Suitable equivalent replacement of components was ensured

at places where the original components were not available.

26

4.8 CONCLUSION The entire project was finally concluded that; this lighting system

and computers would no more loose data or be interfered with

power outage to reduce productivity.

The use of highly inflammable fuels to produce power for lighting

would now be a thing of the past.

The system can be run for a long period of time since it can be

hooked on an external battery.

This project could go a long way to help reduce data loss and the

number of houses brought down by fire due to the use of candles

and other sources of lighting which uses highly inflammable fuel,

and it will help in creating employment for the youth if encouraged in

the country.

57SUMMARY

From the above project it was realized that, this UPS(uninterrupted

Power Supply) system could go a long way to help manage the

power problem since some amount of energy could be stored for

future use, and in this direction help reduce the burden on the

government.

58

RECOMMENDATIONS

My recommendations were based on research made and are as

follows:

1. Firstly, it is highly recommended for health centers such as

clinics, hospitals and maternity homes.

2. Secondly it is recommended for schools.

3. For any one who uses a computer of a system that has a

volatile memory.

4. Thirdly for places where electricity source is not consistent.

5. Furthermore it is recommended for domestic use.

6. Last but not the least; government must encourage such

projects to generate employment for the youth at large.

59

REFERENCES

1. Carols Advance Electronics and Training Centre.

2. www.wikipedia.com/english

Page Copyright © 1995 - Tony van Roon

Project Copyright © 1994, by Fred Blechman

Copyright and Credits:

"Electronics Hobbyist Handbook", Spring 1994. Copyright © Fred

Blechman and Gernsback Publications, Inc. 1994. Published with

permission from Gernsback. (Gernsback Publishing no longer

exists).

Document updates & modifications, all diagrams, PCB/Layout drawn

by Tony van Roon.

Re-posting or taking graphics in any way or form of this project

is expressly prohibited by international copyright laws.