counterpoise, in electronics, portion of an antenna system that is composed of wires or other types of conductor arranged in a circular pattern at the base of the antenna at a certain distance above ground. Insulated from the ground, it forms the lower system of antenna conductors.
Do I need a counterpoise?
No, it is not needed, but it can improve the antenna system. An EFHW is simply a half-wave length of wire and a matching device, and that’s it. Counterpoises are commonly added to shunt common mode reflections when operating outside of the wire’s resonant frequency to avoid RFI issues (“RF in the shack”).
How long should my counterpoise be?
Length of counterpoise should be a minimum of 20-30 feet but longer is better. If possible run the counterpoise above ground away from or perpendicular to the antenna wire and do not ground the counterpoise at the unun. You can also use the unun with no counterpoise or ground if your feedline is at least 25+ feet long.
What is the difference between a counterpoise and a radial?
Radials hug the ground to help provide a low loss return path for the RF that is soaking into the ground. A counterpoise is used to create an artificial ground when an antenna is elevated.
What is a ham radio counterpoise?
A counterpoise is simply a long, insulated wire that attaches to the ground connection on your antenna tuner. The best counterpoise is 1/4-wavelength at the lowest frequency you intend to use. That’s a lot of wire at, say, 3.5 MHz, but you can loop the wire around the room and hide it from view.
What is back flashover?
Back flashover occurs when the lightning strikes on a shield wire or tower, where the resultant voltage across the insulator is large enough to cause a flashover from the tower to the line conductors.
Why earth wire is used in transmission line?
The main purpose of the earth wires is the protection of the conductors against the direct incidence of lightning strokes, that can cause line outages (see Chapter 4).
What is the significance of tower footing resistance?
Low value of tower footing resistance results in less voltage stresses across line insulation. A tower footing resistance of 20 ohm for EHV lines and 10 ohm for HV lines provides sufficient lightning protection. For reducing tower footing resistance, it is better to use ground rod and counterpoise only.
Does a dipole need a ground?
If you use a “complete” antenna like a dipole or a ground plane (that is, one that doesn’t require your feed-line to connect to ground), you don’t need a RF ground, as long as you keep common-mode currents off your feed-line.
How long should a counterpoise be for an end fed antenna?
Length of counterpoise should be a minimum of 30-40 feet but not the same length of the antenna wire. Shorter length counterpoise wires can be used if operation is confined to 40m or higher. Any counterpoise should be at least 1 foot above ground running away from or perpendicular to the antenna wire.
Does a long wire antenna need a counterpoise?
If it is a single wire or a few wires, they should be insulated from earth and kept a little distance above earth. Ideally the single wire counterpoise should be directly under the longwire antenna, and a few feet above earth.
Can you coil a counterpoise?
Or you can use a single counterpoise long enough for the lowest frequency band and coil it back to the appropriate length for higher frequencies.
What is an UNUN for antennas?
Definition & Usage
The UNUN is a “UN balanced to UN balanced” matching transformer. It is used for non-resonant vertical antennas like our 43 foot or 33 foot models.
Does counterpoise affect SWR?
If the antenna system is perfectly tuned to the frequency (channel) that the radio was on in the calibration mode, if the quality of the coax isn’t compromised, if the mount was correctly installed, and if the antenna and counterpoise are in sync, the antenna system will absorb all the power that the radio is putting
Should a counterpoise be elevated?
Projections indicate this system should be within 1-2 dB of sixty radials 100ft long, although optimum performance might require counterpoise heights as much as 0.1 foot above earth per meter wavelength.
What do radials do for a vertical antenna?
Radials are wires arrayed on the surface (or just below it). They provide a low-resistance path for current flowing near those wires. Here’s a diagram from an antenna model showing radials. The diagram actually has eighteen wires in it because two wires were needed to make the vertical portion.
