Well, I suspect that one can't get a complete picture of the correlation between base driving point impedance and radiated field intensity unless we could measure at a multiplicity of elevation angles. Has anyone looked into changes in the elevation pattern as the ground systems are modified? Much easier said than done!!
Charlie, K4OTV -----Original Message----- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of DAVID CUTHBERT Sent: Sunday, December 16, 2012 8:06 PM To: Tom W8JI Cc: topband@contesting.com; Rick Kiessig Subject: Re: Topband: Optimal radial wire type and gauge? Tom, I think you are extrapolating one case with a particular radial length to all vertical antenna ground systems. The N6LF radial papers detail his NEC-4 simulations and measurements of vertical antennas and radial systems. If I read his papers correctly base impedance does track field strength measurements. http://www.antennasbyn6lf.com/ Dave WX7G On Sat, Dec 15, 2012 at 5:10 PM, Tom W8JI <w...@w8ji.com> wrote: > 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 35-40 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" < > telegraph...@gmail.com> > To: "Rick Kiessig" <kies...@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 _______________________________________________ Topband reflector - topband@contesting.com