From the University of Hawaii Ham Radio Club Website:
http://www.chem.hawaii.edu/uham/radials.htmlAbove Ground Solutions
If you are stuck on the second floor of a wood frame house, you can often use a tuned ground wire. A half wavelength of wire will replicate the impedance at the other end. At
15 meters that is about 23 feet. Also there are ground wire tuners available that series tune a random long ground wire to series resonance at any operating frequency. These can be extremely useful where you have to go down the side of a building to an outside groundstake or water faucet two or three floors below. The tuner will allow you to make any length of wire look like the "magic" series tuned length and get rid of any reactance due to the wire length.
But, keep in mind that such a wire will radiate and that radiation will be added or subtracted from the radiation from the antenna, changing its pattern, maybe for the better, probably for the worse.
In fact you can use a series of quarter wavelength wires, one for each band, attached to your tuner to fake a ground. These should be insulated wires since they will be hot with RF. They will be REALLY hot at the far end! I use teflon tape over the end and slip the ends in a section of insulating tubing, leaving the tubing going several inches past the end of the wire. These counterpoise wires can be laid about the floor of a condo apartment many floors up, or wherever you need to fake a ground.
One long one can be used with a ground wire series tuner like made by
MFJ Enterprises and usually called an "artificial ground". Keep in mind the wires must be left floating at the far end in this particular application. In this case the artificial ground will be tuning them as an odd quarter wave multiple, not a half wave multiple as is the case if the end is grounded.
The artificial ground tuners can also be used with grounded wires that have to go a long way to find a decent RF ground, such as dropping out a second floor window to a cold water faucet outside at ground level. In this case they will tune the wire to an electrical 1/2 wavelength and effectively "eliminate" the wire length from the circuit. Though there still can be radiation from this long ground lead to alter antenna patterns, etc.
All these mechanisms replace the missing part of antennas like the end fed random length wire and the quarter wave vertical or the end fed half wave wire. If possible a symmetrical antenna like a center fed dipole, either horizontal or vertical, or a center fed symmetrical random wire using good twin lead or ladder line, will decrease the demands on the station ground and any radial system.