Antenna Types

WB5CXC

Resonant Antennas

• These are antennas that are resonant on the operating frequency.

• The most common is the dipole and it’s derivatives.

1/2 Wave Dipole

Length in feet = 468/ F (Mhz)

50 ohm coax

Current on a Dipole

Higher Current / Lower Voltage

Lower Current / Higher Voltage

Voltage / Current on Antennas

• The center point of the Dipole is low impedance (50 ohm).

• The ends are High impedance. • The center of the Dipole will have 70 volts

with 100 w. • The end will have an impedance of 10K +

ohm which give it a voltage of 1,000+ volts. • Have good insulators at the end of the

antenna.

Inverted Vee Antenna

Inverted ‘L’

Dipole Antennas

• Most Dipole antenna are single band or two bands. (They can work on Odd harmonics – 3rd.)

• They are a good match to 50 ohm coax.

• They should be at least ¼ wave above the ground or higher. (On 80 and 40 this is usually not the case.)

Dipoles Cont’d

• Back in the 60s we made Dipoles with 3 wires.

• The first would be for 80 meters, the second would be for 40 meters, and then the last would be on 10 meters.

• 80 meters would use the 3rd harmonic for 20 meter.

• 40 meters would use the 3rd harmonic for 15 meters.

3 Wire Multi-Band Dipole

Dipoles Cont’d

• You can make a multi-band antenna by using traps. The highest frequency is the first portion and the lower frequency uses the entire antenna.

• The traps will also shorten the antenna somewhat.

10 M

20 M

10M Trap

2 Band Trap Dipole

Traps Cont’d

• The Trap is a parallel resonant circuit. At resonance it presents a very high impedance.

• This high impedance acts like an ‘Open’ circuit and disconnects the rest of the antenna.

• Off resonance the impedance is low and acts like a ‘Short’ thus connecting the two parts of the antenna.

Trap

= 2 f L 2 f C

1

fXC( ) XL( )

If you reduce the frequency , then the Trap becomes Capacitive !!

XLXC =

10 M

20 M

10M Trap

You cut the longest part of the antenna to work on 20M.

XLfr =XC=

With the Trap in the circuit and you lower the frequency it becomes Capacitive and thus reduces the resonant frequency (which effectively makes the antenna shorter).

(The antenna was cut for 14.2 Mhz, but now it tunes to 13.9 Mhz [too Long now]– you have to cut the antenna to make it tune to 14.2 Mhz.)

Verticals

• Verticals antenna are usually a variation of the ½ wave dipole. The vertical is only ¼ wave and the ground reflection provides the other half of the dipole.

• Optimum vertical operation depends on a good ground. This is usually made with radials buried in the ground.

¼ Wave Vertical

Verticals Cont’d

• Traps can be added to verticals to provide multi-band operation.

• There are several advantages of verticals, the main advantage is that it requires less real estate and height.

• The vertical are a true Omni directional antenna and they have a low angle of radiation.

Verticals Cont’d

• Trap vertical have a height of 10 – 30 feet.

• One of the newer popular verticals is the 53 foot. This uses no traps and works most bands (best on 80 – 20M). It requires an antenna turner at the base (similar turner as a long wire turner).

Vertical Dipoles

• Vertical Dipole antennas is a new concept to amateur radio (within the last 5 years).

• It looks like an ‘H’ turn on it’s side or some call it a double ‘T’.

• It uses capacitance hats to shorten the elements.

• They require less real estate and also have approximately the same gain as a dipole.

Sigma 6M Vertical Dipole

36"

20" X 5/8" Tubing20" X 5/8" Tubing

20" X 5/8" Tubing 20" X 5/8" Tubing

60" X 1" Tubing

Vertical Dipoles Cont’d

• They mount low to the ground.

• The coax has to come off at ~ 45 degrees.

• They have a low angle of radiation.

• Sigma (Texas Antennas) and Transworld Antennas are two manufacturers of vertical dipoles.

• They also have multi-band vertical dipoles.

Non Resonant Antennas

• There are also Non Resonant antennas.

• The Long Wire antenna is a Non Resonant antenna.

• It is multiple wave lengths long. When we think of a Long Wire antenna we think of an wire that is 200+ feet long.

• Tuner is under the antenna and takes a different kind of turner.

Tuner

200' +

Long Wire Antenna

G5RV Antenna

• G5RV antennas are multi-band antennas.

• They are not a resonant antenna (except maybe on 20M).

• They will work most bands 80 – 10 (not useful on 30, 17, 10M [by some comments])

• They look like a dipole except that on the center insulator it will have 450 ohm ladder line.

G5RV Cont’d

• The ladder line has to hang vertical and can not be near anything.

• You need an antenna tuner for this antenna.

• Normal size is 102’ top and 30’ of 450 ladder line – need ~70’ of coax for antenna to perform properly.

G5RV Cont’d

• G5RV Jr. is 51’ top and 17’ of 450 ladder line – need 35’ of coax for antenna to perform properly. This antenna is good for 40M and up.

• The ladder line is part of the antenna and radiates.

G5RV Antenna

450 ohm ladder line

G5RV Cont’d

• There is a lot of FOLK Lore about the G5RV.

• Some swear by it -- others say it is worthless.

• You need to be aware of what it will do and the pitfalls.

• Most of the poor operation is do to bad installations.

G5RV Cont’d

• The antenna should be higher than 34’.

• The top of the antenna needs to be inline.

• The ladder line has to hang straight down and not touch anything or be near anything.

• Should have long lengths of coax for it to work properly.

Gain Antennas

• Gain antenna use power radiated in unwanted areas and puts it into a more useable pattern.

• On a Dipole a lot of power is goes up in the air, most of us are not talking to planes so this is wasted power. We also are not talking to stations behind us.

• We direct this wasted energy into a more useable direction (in front / and lower).

Gain Antennas Cont’d

• The most common Gain antenna is the Yagi.

• Other Gain antennas include the Cubic Quad, Hex Beam, Moxon.

• In the HF bands these antenna can become quite large and you need a rotor to turn them.

Yagi Antennas

• A Yagi antennas has 2 or more elements.

• The simplest is a 2 element Yagi – Reflector & Driven Element (Driver)

• The Reflector is the longest element it is ~ 10% longer than the Driver.

• The Driver is where you feed the antenna.

• On multi-element Yagis you added Directors (shorter than the Driven element).

3 Element Yagi Antenna

Reflector

Driven Element

Director

Direction of

Radiation

Yagi’s Cont’d

• Yagi come in single band or multi-band.

• Probably the most popular is the Tri-Band Beam with traps – 10, 15, 20. (Reduced size)

• Some of the multi-band beams have multiple element and become quite large (and expensive – need big towers and rotators).

Moxon Antenna

• A Moxon antenna is a 2 element antenna with bent elements.

• It is smaller than a normal 2 element Yagi.

• It can be built using normal items from a hardware store and can use wire for the elements.

• Spacing and dimensions are critical.

• Use Moxongen.exe for the design.

Direction of R

adiationDriven Element

Reflector

Moxon Beam

10M Moxon – PVC & Wire

Hex Beam

• Hex Beams are another reduced sized beam.

• It used bent elements (wires) and a non-conductive frame.

• Frame is usually fiberglass rods.

• The frame is made with 60 degree angles.

• The name comes from beam configuration – 8 sided (Hex).

Hex Beam Cont’d

• Hex Beams are usually multi-band and can have up to 5 bands on one antenna.

• They bend the rods and string the wiring.

• It looks like an upside down umbrella.

• There is a lot of information on the Internet to build your own.

• Commercially manufactured by Traffie Technology and others.

Hex Beam

Driven Element

Reflector

Non-Conductive Frame

Hex Beam