Technician Class License Course Chapter 4

Practical Antenna Systems Sec 4.4

26 Jan 18 K0NK

The Dipole Pg 4-11

• 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

Typical HF Dipole Installation Pg 4-11

Most dipoles on the lower bands are oriented horizontally and radiate a horizontally polarized signal. Broadside Radiation Pattern Pg 4-11

Dipoles radiate the strongest signal broadside to the axis of the dipole Broadside Radiation Pattern Pg 4-11

Azimuthal Pattern Computer Generated Sketch Dipole Length Pg 4-12

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

7 Dipole Length

 Typical lengths for common ham bands

We shorten the antenna to raise the frequency Building a Dipole

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 Measurements 4-10

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

10 Common Dipole Configuration Fan Dipole

The Ground-Plane Pg 4-12 The Ground-Plane

• Is simply a 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 Vertical

A very common antenna is the ¼ λ vertical The 5/8 λ Ground Plane

 More than twice the length of a ¼ λ.  About 48 inches  Focuses more energy towards the horizon.

 Uses and inductive loading coil at the base to make the antenna electrically longer. Ground Plane Gain

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

 The short flexible antenna on a Handie Talkie is often called a Rubber Duck Rubber Duck Performance Pg 4-13

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--especially inside a car.  Connecting to an external mobile antenna DRAMATICALLY improves the operation of your HT. = Handheld Antennas

 Rubber duck operating tips  Hold the transceiver vertical  Keep antennas aligned in polarity  Misaligned antennas can reduce signals by 100 times  For best HT performance,  Abandon the rubber duck  Connect to an external antenna  Especially in a car Mobile Antenna 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) Loop Antennas – Dipole Variations

• Quad • Delta • Horizontal Directional (Beam) Antennas Pg 4-14

• 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). Directional (Beam) Antennas Pg 4-14

Yagi Quad

Horizontally polarized Yagis and Quads are used for long-distance VHF and UHF communications. Horizontal polarization has less ground losses. Directional (Beam) Antennas Pg 4-15

• All beam antennas have parts called elements. – Driven element connected to the radio by the feed line. – Reflector element is on the back side. – Director element(s) is on the front side toward the desired direction. Directional (Beam) Antennas Pg 4-14

• 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. The Dish is a Directional Antenna Pg 4-14

 Used at frequencies above 1 GHz.  Focus energy  Provides gain World’s Worst Antenna! However it has a very good SWR

 The Dummy Load  Is used to prevent radiating signals when making a test transmission.  Dissipates the power into heat instead of radio waves. Coax Feed Lines Pg 4-16 • RG-58 • RG-8 • RG-213 • RG-174 • Hardline

• All these are 50 Ω impedance 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 Pg 4-16

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

or LMR-400

See Table 4-1, Page 4-16

RG-8 will have lower loss than the smaller RG-58 Coax Connectors Pg 4-17

• UHF – SO-239/PL259 – Used at HF frequencies • BNC • SMA • N – Used at frequencies above 400 MHz

Seal the Coax Connectors Pg 4-17

• Water in the coaxial cable degrades the effectiveness of the braided shield • Air-core coaxial cable requires special techniques to prevent water absorption

Soldering

http://stomach.v2.nl/projects/Basic_Electronics/Soldering.pdf

http://w6rec.com/duane/bmw/solder/ Soldering Pg 4-17

 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

Feed Line Devices

• Balun • Duplexer • Antenna switches • SWR meter • Antenna analyzer • Antenna tuners SWR Meter / Directional Wattmeter Pg 4-18

SWR Meter Directional Reads out SWR Wattmeter • Forward W • Reflected W

Reads out SWR and Forward and Reflected Power 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 Antenna Analyzer Pg 4-19

 An antenna analyzer can be used to measure the SWR of an antenna.  Does not require a transmitter Antenna Tuner Antenna Tuner Schematic

42 How to use an Antenna Tuner Pg 4-18

• 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 All-Band Dipole 80 – 10 m G5RV All-Band Dipole Random Wire Antenna Antenna Tuner Pg 4-18

• One way to make antenna matching adjustments is to use an antenna tuner. • Antenna tuners are impedance transformers (they actually do not tune the antenna). – When used appropriately they are effective. – When used inappropriately all they do is make a bad antenna look good to the transmitter…the antenna is still bad. Duplexer

 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 Tuners

• Don’t really “tune the antenna” • Matches the antenna system impedances to the transmitter’s output impedance • Reduces the SWR the transmitter sees • Antenna feed point impedance unchanged • Feed line SWR unchanged • Also called impedance matchers, transmatches, matchboxes, other trade names

2014 Technician License Course How to Use an Antenna Tuner

• Transmit a low-power signal • Monitor the SWR meter • Adjust the tuner until minimum SWR is achieved

2014 Technician License Course Antenna Supports

• Trees. • Towers or masts. • Covenants and antenna restrictions must be considered. • Stainless steel hardware resists corrosion.