Aluminum foil is not just for making hats anymore. Here is the section on ground system testing from Radio Works.
http://www.radioworks.com/nbgnd.html
A ground system test
OK, so you have a good ground system set up, all the ground wires are short, all the ground loops have been minimized. Can the system be improved? Probably, and here is a quick and simple way to find out. This test is especially good for checking out radial systems for verticals and ground systems on boats.
First, purchase two, inexpensive, 75' rolls of aluminum foil. Unroll about 8 feet of foil from each roll and lay in on the ground, the rolls forming a 90 degree angle to one another. Twist the first foot of foil into a thick, aluminum wire. Then twist the two twisted ends of the foil together. Use a short clip lead or other attachment method and connect the foil to the ground system. Even better, connect a length of ground braid and route it directly to the point on the transmatch in the shack. Measure your antenna's SWR with and without the foil ground hooked up. It shouldn't make any difference. If it does, then you need a better ground system. Repeat this procedure for each band, unrolling the length of the foil so it is 1/4 wavelength long for the band being tested. If your ground system is working well, there will be no difference in SWR readings.
There are other ways to make this measurement beside looking for changes in SWR. If you have an RF ammeter, (the MFJ-931 has one built-in) connect it in series with the station ground at the transmitter. Use the aluminum foil procedure outlined above. Any change in RF ground current indicates an inadequate ground system. The MFJ RF 'Current Probe' should work as well and does not have to be placed in series with the ground systems.
The foil technique works well with vertical antennas. Roll out a coupe of lengths of foil for a particular band, connect to the base of the vertical in parallel with the radial system. If the SWR changes, the radial system could use some improvement.
Note: With an improved ground system, you may see the SWR rise slightly. Remember, a properly installed 1/4 wave vertical with low I2R losses will have a feedpoint impedance around 30 - 35 ohms. The lowest SWR you will see if everything is working perfectly is 1.5:1. Trap verticals are certainly no better than a good, full-size, 1/4 wave vertical. So, don't be surprised to see the SWR increase as the ground losses are reduced.
