Ground vs Counterpoise
the least understood HAM radio topic
Amateur radio stations have three unique and separate "grounding" functions;
- Electrical (Safety) Ground
- Station (RFI) Ground
- Antenna (Counterpoise) Ground
Electrical Safety Ground is a connection to chassis to prevent operator contact with dangerous voltage if electrical power supply insulation fails. This connection provides a return path to trip the circuit breaker.
Station RFI Ground is a single point at which shack equipment ground lugs are connected together through a very short, low impedance lead, so any RF that reaches the station will be shunted to Earth.
Antenna (Counterpoise) Ground is the other half of the antenna. Normally a wire, one-quarter wavelength long. It does not need to be straight. Placing radials in soil DEGRADEs effectiveness compared to elevated radials but in ground is more practical. A BALUN is needed to isolate the antenna common mode current from the station.
Why you need a good Counterpoise
A vertical antenna has two key components in radiation; the vertical and a ground plane are required and equally important. There are numerous articles on ground planes. In this case the radials the better you only get some relief on length again near a quarter-wavelength is best. The idea of a good ground plane is to reflect the maximum of your radiated signal, and stop it being absorbed in the ground. It also reflects the received signal into your antenna and improves the low angle pattern for DX. You can't work them, if you can't hear them. Radials of any length are better than none, but ideally a quarter-wavelength. If space is a problem zig zag or some long and some short ground wires is a backup plan, this works and is better than all short radials. Most lots urban are not large enough for this type of installation, but, with some creative thoughts, great things can be achieved. Review the following slides and determine the best layout for your property.
Guidance for your Ground Plane
• Local soil resistance is high & more radials are required, generally 64 radials in the best idea
• Use 16 radials minimum but 4 radials 1 foot above ground are better than 32 in the ground
• Length is more important than an absolute number
• Cut to ¼ WL plus 5% for lowest frequency
• Radials can be “bent” around house if needed
• Copper, Galvanized or Aluminum
• Cut slit in grass with edger
• Connect at base of antenna vertical
• Hidden Dog Fence vendor will charge $150 to $200 for 16 Radials
• Ground Radial Plate Kit
One thing to consider before you built a vertical monopole
If you have poor soil conditions, dry, sand, rocks, etc. it is next to impossible to get a "Typical" performance from in ground radials. If it is possible to have two radials one foot above ground (i.e. in the bushes) are better than 30 in the ground. If above ground is not possible you can see in the figure below an low dipole will give the same DX results. If you decide to have a monopole be sure to design a dedicated counterpoise as part of your monopole design and placement.
Typical 100W T/R on 40 M shown above with four different antennas
Antenna Height and Communications Effectiveness
By R Dean Straw. N6BV, Gerald L. Hall. K1TD
DX openings are few above 15° Elevation, improvements can be realized by;
• Increasing the height of the antenna
• Raising the ground plane 1 to 5 Feet above ground
• Use a Vertical Dipole or J-Pole that do not require Ground Plane, but are 2X, 3X taller
• Put in 16 (or better 32) Radials if not an attic dipole will be a better DX antenna choice √
Solid Ground Connections are just as important as more radials
• Bond mechanically and electrically
• Use anti-corrosion paste
• Keep connections dry