Antennas: Safety Ground, RF Ground, Lightning GroundBy Gary, K9SG

A ground actually has several meanings: Safety ground, RF ground, Lightning ground. For a vertical antenna the RF ground usually consists of radial wires which provide an electrical counterpoise or RF ground. The vertical is like 1/2 of a dipole and needs to have a ground that works at RF frequencies. Generally speaking about 30 radial wires that are about 1/6 wavelength either on the ground or slightly under the ground work well if the soil has good conductivity. The conductivity of the ground under the antenna determines the takeoff angle of the signal where the maximum radiation occurs. The angle is measured from the plane of the ground up. Conductive soil helps lower the radiation angle which gives better long distance signals. Soil conductivity out here is not good compared to where I am from in Indiana. If your antenna has counterpoise radials I don't know if using radials would help that much. If you have the antenna within a few feet of the ground the radials would probably help some. See my PowerPoint on vertical antennas.

For lightning ground the normal thing to do is to have 2 or 3, 8 foot ground rods 8 or more feet apart connected to the base of a high vertical antenna or tower to couple with the ground and provide lightning a path to ground other than your coax cable coming into your ham station. Out here it might be better to have one ground rod and put 6 to 8 6 ft. or longer # 6 wire about 1 or 2 feet under the ground. Generally speaking if you have a vertical antenna or tower under 50 feet it is not more likely to get hit than anything else in the area. They can pick up a big surge from local strikes and it is still a good idea to protect them at least with a ground rod and a few feet of copper wire underground.

Safety ground is your grounding system in your house with GFIs, common ground, grounded entry, etc.

Your station ground should have everything grounded to an aluminum or copper bar that is grounded to an outside ground system. At least 2 or 3 ground rods 8 feet apart connected by number 6 copper wire. You should ground your coax shield to this, get a lightning arrester built by someone like Morton Manufacturing that has MOV devices to protect from lightning, and a coax lightning suppressor made by Alpha-Delta, Polyphasor, or Morton. Everything going to AC needs to plug into your AC suppressor, your radio ground, tuner ground, computer ground should also be connected to this point.

This guy wrote a good article on grounding

https://www.w8ji.com/station_ground.htm

Following is a PowerPoint presentation I gave that has some information about ground conductivity and radiation angles from vertical antennas.

As a general rule I think dipoles for 20 through 10 meters work better than verticals out in our area if you can get them up 1/2 wavelength or more. A 40 dipole will probably do better at 60

feet than a vertical especially for non-DX operation. When you get to 80 and 160 verticals are usually going to be better unless you can put a dipole up 150 feet. Good Luck with ham radio

73Gary K9SG

ANTENNAS Dipole Antennas Beam Antennas – Yagis, Log Periodics, Quads Vertical Antennas Vertical Arrays Receiving Antennas What is Practical for a Given Goal

Refractions Reflectionsand Launch Angles

F Region

D Region

Earth Reflection

1 2 3

ISS

Wave Angle vs. Transmission Distance

What is the Optimum Launch Angle

Minimum DX – 1Hop

Maximum DX 4 or 5 Hops

Choosing an antenna Radiation Pattern – Omni or directional Forward gain and 3db beamwidth Launch Angle (local vs. DX) Front to back ratio (Reduce QRM & Static) SWR over Band (Avoid using tuner) Cost (Budget and Scrounging ability) Weight (Tower size $$ Rotor size $$) Managing the beast (Installing &Maintaining) Choosing Coax

Coax loss per 100 ft SWR 2:1 db loss is linear for length

Frequency RG8 X * RG8 9913 ½ Andrew

2.0 MHz 0.4 db 0.25 db 0.15 db 0.1 db

4.0 MHz 0.56 db 0.3 db 0.24 db 0.12 db

7.0 MHz 0.75 db 0.45 db 0.3 db 0.17 db

14 MHz 1 db 0.6 db 0.45 db 0.2 db

21 MHz 1.3 db 0.8 db 0.55 db 0.3 db

28 MHz 1.5 db 0.9 db 0.65 db 0.35 db

50 MHz 2.1 db 1.3 db 0.85 db 0.46 db

* Note RG8 X rated 1 KW to 7 MHz 350 W at 50 MHz

Coax loss per 100 ft SWR 2:1 db loss is linear for length Choices for 100 ft of coax

Frequency RG8 X * RG8 9913 ½ Andrew

2.0 MHz 0.4 db 0.25 db 0.15 db 0.1 db

4.0 MHz 0.56 db 0.3 db 0.24 db 0.12 db

7.0 MHz 0.75 db 0.45 db 0.3 db 0.17 db

14 MHz 1 db 0.6 db 0.45 db 0.2 db

21 MHz 1.3 db 0.8 db 0.55 db 0.3 db

28 MHz 1.5 db 0.9 db 0.65 db 0.35 db

50 MHz 2.1 db 1.3 db 0.85 db 0.46 db

* Note RG8 X rated 1 KW to 7 MHz 350 W at 50 MHz

Coax loss per 100 ft SWR 2:1 db loss is linear for length Choices for 200 ft of coax

Frequency RG8 X * RG8 9913 ½ Andrew

2.0 MHz 0.4 db 0.25 db 0.15 db 0.1 db

4.0 MHz 0.56 db 0.3 db 0.24 db 0.12 db

7.0 MHz 0.75 db 0.45 db 0.3 db 0.17 db

14 MHz 1 db 0.6 db 0.45 db 0.2 db

21 MHz 1.3 db 0.8 db 0.55 db 0.3 db

28 MHz 1.5 db 0.9 db 0.65 db 0.35 db

50 MHz 2.1 db 1.3 db 0.85 db 0.46 db

* Note RG8 X rated 1 KW to 7 MHz 350 W at 50 MHz

Coax loss per 100 ft SWR 2:1 db loss is linear for length Choices for 300 ft of Coax

Frequency RG8 X * RG8 9913 ½ Andrew

2.0 MHz 0.4 db 0.25 db 0.15 db 0.1 db

4.0 MHz 0.56 db 0.3 db 0.24 db 0.12 db

7.0 MHz 0.75 db 0.45 db 0.3 db 0.17 db

14 MHz 1 db 0.6 db 0.45 db 0.2 db

21 MHz 1.3 db 0.8 db 0.55 db 0.3 db

28 MHz 1.5 db 0.9 db 0.65 db 0.35 db

50 MHz 2.1 db 1.3 db 0.85 db b0.46 d

* Note RG8 X rated 1 KW to 7 MHz 350 W at 50 MHz

The Dipole AntennaStandard Dipole ½ Wavelength73 Ohm Impedance Free Space50 Ohms when near groundBandwidth about 5% of Frequency

Folded Dipole 1 wavelength Current ½ voltage 2X300 Ohm Impedance Free Space300 Ohm Feed ImpedanceWider Bandwidth

Dipole Horizontal Radiation vs.Elevation Angle of Signal

Wave Angle vs. Dipole Height

30

15

7.5

Elevation & Dipole effectiveness Compared to 1.5 WL @ 10 deg Launch Angle for DX

PeakTakeoffAngle

Relative Gain

Elevation Wavelength

80 M 40 M 20 M 15 M 10 M

45 deg - 15 db ¼ WL 68 ft 34 ft 17 ft 13 ft 9 ft

30 deg - 7 db ½ WL 140 ft 68 ft 34 ft 25 ft 17ft

15 deg - 1 db 1 WL 280 ft 140 ft 68 ft 50 ft 34 ft

10 deg ------- 1.5 WL 420 ft 200 100 ft 75 ft 50 ft

8 deg +1 2 WL 600 ft 280 ft 140 ft 100 ft 68 ft

Professor Yagi 1926Uda probably did the work

InductiveReactance

CurrentLagsVoltage

CapacitiveReactance

Current Leads Voltage

Yagis compared to Dipoles

HF Yagis typically have a forward gain of 3 to 9 db over a dipole (2X to 8X the effective power)

They also increase received signals by the same amount wow!

They have a slightly lower takeoff angle compared to dipoles at the same height for better DX

10 to 25 db front to back and front to side ratio to decrease QRM and Noise

Yagi Antennas of Optimum Design for 20 Meters

EL Gain overDipole

Weight BoomLengthTruss *

TurningRadius

WindLoad

2 3 db 16 # 6 ft 19 ft 2.5 sq ft

3 6 db 25# 16 ft 22 ft 4.0 Sq ft

4 7.6 db 45# 34 ft * 25 ft 6.7 sq ft

5 8.5 db 80# 44 ft * 28 ft 10 sq ft

6 9 db 125 # 58 ft * 40 ft 15 sq ft

Little 4 foot 900 MHz Yagi

Super Yagis Tower 100 Meters 80 M 4 el @ 90 M 160 M 3 el @ 80 M Wt. 40 tons Boom 215 ft. Boom is triangle

7 feet per side with a walkway

$3 to 5 million ?

160 Meter boom to element

Integrated Walkway

Cubical Quad Antennas

Cubex 2 element Quad

Quads vs. Yagis Less noisy on receive 5 band quad cheaper than 5 band yagi Broader first takeoff lobe and Lower Launch at

lower height (works better than Yagi at lower heights)

1 db gain over a Yagi? Not as sturdy as a Yagi Is 3D and hard to put up Wire elements tend to break easily Difficult to make for lower bands

Stacking Yagis for Gain & Launch

20 Meter Gain Comparisons Relative to dipole at 30 feet for DX Very rough cost comparisons

Height Dipole 2 El Yagi+ 4 db

3 EL Yagi+ 6 db

6 El Yagi + 9 db

Stack of 650 100 150

35 ft 0 db$100

4 db $1500

6 Db $1700

9 db $2200

70 ft + 4 5 db $300

8 db $2000

10 db $2700

13 db $3700

100 ft + 6 6 db $1600

10 db $4000

12 db $4200

15 db $5600

120 ft + 8 8 db $3000

12 db $5000

14 db $5200

17 db $7200

Stack 22 db $25,000

Vertical Antennas

Vertical Antennas Gain about 2.5 db less than dipole They work much better over good earth than bad

earth ground and are magic near salt water (ocean beaches)

Radials are necessary for good performance 30 1/8 WL WL radials almost as good as 120 ¼ WL radials over good earth

Impedance approaches 36 ohms with conductive soil, on the beach, and big radial systems

Advantage on 160 all the time, 80 most of the time, and 40 ~ same as dipole at 80 ft.

Verticals What makes them work well

Efficiency determined by antenna length and ground conductivity

Far-field (1-4 WL) ground **Launch angle Quarter Wave Verticals work best most of the

time and are easy to model Short loaded verticals require better grounds,

are less efficient and have narrower bandwidths Increasing the diameter of the radiating

element increases bandwidth

Verticals What makes them work well

Ground Conductivity location location location

Efficiency 100% hard to achieve

Launch angle Very small in proper setting

Length of Antenna Quarter wave is best

Shortened Verticals - Always a compromise

Choosing the right radial system Increasing the Bandwidth Phasing for more Gain

Ground Conductivity Current Density at Depth

Ground Conductivity and the Pseudobruester angle

Radials – The effect on Gain and Radiation Angle

Gain Radiation Angle

8 deg 19 deg

24 deg 28 deg

Length vs. Efficiency

Resistance of Radial systems The lower the better

Efficiency of Loaded Verticals

Antenna WavelengthIn Degrees

Efficiency

Loss in db

90 degrees no loading 75% 1db

45 deg top loaded 62% 1.5 db

45 deg bottom loaded 37% 2 db

10 deg top loaded 9% 10 db

10 deg bottom loaded 2% 18 db

4 Sq Patterns Forward gain ~ 5.5 db

over single vertical Front to back ratio

over 25 db Everything behind

over 12 db down 3 db Beamwidth ~90

degrees Switch directions

instantly

Inverted L used on 80 & 160

Sources of up to date Info WWV reports DX – Summit

http://www.dxsummit.fi/Default.aspx Propagation Page

http://dx.qsl.net/propagation/ QST and CQ columns on propagation Carl K9LA Propagation guru from Ft. Wayne

http://mysite.ncnetwork.net/k9la/