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 <w8ji@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" <
> 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
|