There is no magic about 120 radials, and long before 120 radials are reached
the increase in field strength pretty much stops.
At my house around 30 radials or so, about 1/4 wave long, go flat on
efficiency increase on 160 meters.
I could have a million radials and it would be insignificantly different
than 30 radials when they are 1/4 wave long here.
I found this by measuring field strength, and I also found feed resistance
change did NOT necessarily track the field strength changes. Good luck
on using base impedance to determine effiency changes! In a 40 meter test,
for example, one ground system provided 3540 ohms of feed resistance and
another different system that provided almost 60 ohms of feedpoint
resistance had equal field strength.
I think N6RK and others have measured the same.
73 Tom
 Original Message 
From: "DAVID CUTHBERT" <telegrapher9@gmail.com>
To: "Rick Kiessig" <kiessig@gmail.com>
Cc: <topband@contesting.com>
Sent: Saturday, December 15, 2012 10:49 AM
Subject: Re: Topband: Optimal radial wire type and gauge?
Read the N6LF radial papers and you will see that 1/8 wavelength radials
are about as good as one can do. I use #14 stranded copper THHN wire
because it is easy to work with.
But how good can we get? For a 30' base loaded vertical I have 90 radials
having an average length of 18 ft. The ground loss is 5 ohms, which is
less
than the loading coil loss. If I were to install 120 quarter wavelength
radials I would gain 2 dB.
Dave WX7G
_______________________________________________
Topband reflector  topband@contesting.com
_______________________________________________
Topband reflector  topband@contesting.com
