technician class license course chapter 4

Technician Class License CourseChapter 4

Practical Antenna SystemsSec 4.4

2021K0NK

The Dipole

• The most basic antenna — The Dipole

– Two conductive, equal length parts.

– Feed line connected in the middle.

• Dipoles are easy to make and easy to use

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Typical HF Dipole Installation

Most dipoles on the lower bands are oriented horizontally and radiate a horizontally polarized signal.

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Broadside Radiation PatternPg 4-11

Dipoles radiate the strongest signal broadside to the axis of the dipole

Broadside Radiation PatternPg 4-11

Azimuthal Pattern Computer Generated Sketch

Dipole Length

7

Total length is ½ wavelength (1/2 l )

Estimated Length (in feet) = 468 / Frequency (in MHz)

• For 146 MHz: 468 / 146 = 3.2 ft = 38.5 inches

• For 50 MHz: 468 / 50 = 9.33 ft = 112 inches

• For 28.5 MHz: 468 / 28.5 = 16.4 ft

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Dipole Length

Typical lengths for common ham bands

We shorten the antenna to raise the frequency

4-13

Building a DipolePractical Information

Hint: Make the element a few percent longer than needed, then check the SWR. Shorten the antenna until it is resonant at the desired frequency.

SWR MeasurementsPractical Information

10

The length of each leg of the antenna is adjusted to provide a low SWR on your favorite part of the band.

Common Dipole ConfigurationPractical Information

Fan DipolePractical Information

The Ground-PlanePg 4-14

The Ground-Plane

• Is simply a variant of the dipole that is oriented perpendicular (vertical to the Earth’s surface).

• One half of the dipole is replaced by the ground-plane.– Earth

– Car roof or trunk lid or other metal surface.

– Radial wires.

• Length (in feet) = 234 / Frequency (in MHz).– For 146 MHz: 234 / 146 = 1.6 ft = 19.2 inches

Quarter Wavelength VerticalPractical Information

A very common antenna is the ¼ λ vertical

The 5/8 λ Ground Plane

A 5/8λ antenna is more than twice the length of a ¼ λ.

About 48 inches at 2m (146 MHz)

Focuses more energy towards the horizon.

Ground Plane Gain

A 5/8 λ antenna focuses more energy toward the horizon

Loading Coil

An inductor (coil) in the radiating portion of an antenna can make the antenna electrically longer.

Rubber Duck

The short flexible antenna on a Handie Talkie is often called a Rubber Duck

Rubber Duck Performance

The built in Rubber Duck antenna on a Handie Talkie (HT) performs poorly – It does not transmit or receive as effectively as a full sized antenna

Signals from inside a car, with HT’s integral antenna,might not propagate well due to the shielding effect of the vehicle

Connecting to an external mobile antenna DRAMATICALLY improves the operation

of your HT.

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Handheld Antenna Tips

Rubber duck operating tips

Hold the transceiver vertical

Keep antennas aligned in polarity

Misaligned antennas can significantly reduce signal strength

For best HT performance,

Abandon the rubber duck

Connect to an external antenna

Especially in a car

- MAG-MOUNT -Antenna with a magnetic base

and feedine

Mobile Antenna Mount Types

Mobile Antenna Mounts

Mag- Mount

Through-hole mount

Trunk/hatch lip mount

Number of Bands

Single Band

Dual Band (2m/70cm)

Multi Band (2m/1.25m/70cm)

Directional (Beam) Antennas

• Beam antennas focus or directs RF

energy in one direction.

– Gain

• An apparent increase in power in the desired

direction (both transmit and receive).

• Yagi (rod-like elements – TV antennas).

• Quad (square wire loop elements).

• Dish (shaped like a dish or bowl)

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Directional Antennas

Quads

YagiPg 4-16

* Yagis, Quds and Dish antennas are common types of directional antennas

* Horizontally polarized antennas are used for long-distance VHF and UHF communications. Horizontal polarization has less ground losses.

Dish

Directional (Beam) Antennas

• Beam antennas are usually pointed at the

station you want to talk to.

• Sometimes a beam can be pointed at a

distant object or structure to reflect the

signal around a building or hill that is

obstructing a direct line-of-sight signal.

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Coax Feed Lines

• RG-58

• RG-8

• RG-213

• RG-174

• Hardline

• All these are 50 Ω impedance

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Coax Feed Lines LossPg 4-17

146 MHz

Transceiver

100 ft RG-8 Coax has 2.5 dB loss

50 Watts of Power

28 Watts of Power

Example of Coax Loss:

Coaxial Cable (Coax)

Has an outer jacket to keep water out.

Prolonged exposure to ultraviolet light can cause the plastic jacket to degrade (crack).

Water degrades the effectiveness of the shield.

Water damage dramatically increases loss.

All coax cables have loss

Loss increases at the higher frequencies

Coax Loss

Remember: 3 dB of loss = ½ of your power is lost

See Table 4-1, Page 4-17

RG-8 will have lower loss than the smaller RG-58

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or LMR-400

Coax Connectors

• UHF– SO-239/PL259

– Used at HF frequencies

• BNC

• SMA

• N– Used at frequencies

above 400 MHz

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Seal the Coax Connectors

• Water in the coaxial cable degrades the effectiveness of

the braided shield

• Coax Connectors exposed to the weather should be

sealed.

• Air-core coaxial cable requires special techniques to

prevent water absorption.

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Soldering

Soldering tutorial: http://w6rec.com/duane/bmw/solder/

Soldering

Antenna/coax work may require soldering

For antennas and other electronic use, use only rosin-core solder

Heat the connection well with a soldering iron.

Good joints are shiny

Bad or “cold” solder joints have a grainy or dull finish

DO NOT USE ACID CORE SOLDER

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Feed Line Devices

• Balun

• Duplexer

• Antenna switches

• SWR meter

• Antenna analyzer

• Antenna tuners

SWR Meter / Directional WattmeterPg 4-18

SWR Meter

Reads out SWRDirectional

Wattmeter• Forward W • Reflected W

Reads out SWR andForward and ReflectedPower at the same time

Pay attention to the specified usable frequency range.

SWR Meters

• Measure SWR directly by sensing power

flow in the line

• Usually installed at the transmitter

2014 Technician License Course

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Antenna Analyzer

An antenna analyzer can be used to measure the SWR of an antenna.

Does not require a transmitter

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http://www.mfjenterprises.com/pictures/MFJ-259B.jpg

Antenna Tuner

Antenna Tuner Schematic

40

How to use an Antenna Tuner

• Monitor the SWR meter.

• Make adjustments on the

tuner until the minimum

SWR is achieved.

– We are matching the

antenna system’s

impedance to the

transceivers output

impedance

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All-Band Dipole 80 – 10 m

World’s Worst Antenna!However it has a very good SWR

The Dummy Load

A Dummy Load is used to prevent radiating signals when making a test transmission.

Dissipates the power into heat instead of radio waves.

DuplexerPractical Information

Allows two radios (or a dual-band radio) to share one antenna.

Many dual band radios have the duplexer built in

2 m

70 cm

Antenna Supports

• Trees.

• Towers or masts.

• Covenants and

antenna

restrictions must

be considered.

• Stainless steel

hardware resists

corrosion.

A. Right-hand circular

B. Left-hand circular

C. Horizontal

D. VerticalT3A03 HRLM (4-15)

What antenna polarization is normally used for

long-distance weak-signal CW and SSB contacts

using the VHF and UHF bands?


A. Ultraviolet resistant jackets prevent harmonic radiation

B. Ultraviolet light can increase losses in the cable’s jacket

C. Ultraviolet and RF signals can mix, causing interference

D. Ultraviolet light can damage the jacket and allow water

to enter the cableT7C10 HRLM (4-16)

Why should the outer jacket of coaxial cable

be resistant to ultraviolet light?


A. Ultraviolet resistant jackets prevent harmonic radiation

B. Ultraviolet light can increase losses in the cable’s jacket

C. Ultraviolet and RF signals can mix, causing interference

D. Ultraviolet light can damage the jacket and allow

water to enter the cableT7C10 HRLM (4-16)

Why should the outer jacket of coaxial cable

be resistant to ultraviolet light?


A. 112

B. 50

C. 19

D. 12T9A08 HRLM (4-11)

What is the approximate length, in inches, of a

quarter-wavelength vertical antenna for

146 MHz?


A. Inserting an inductor in the radiating portion of the

antenna to make it electrically longer

B. Inserting a resistor in the radiating portion of the antenna

to make it resonant

C. Installing a spring in the base of a mobile vertical

antenna to make it more flexible

D. Strengthening the radiating elements of a beam antenna

to better resist wind damage

T9A14 HRLM (4-13)

Which of the following terms describes a type of

“loading” when referring to an antenna?


technician class license course chapter 4

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