Topband: Modeling "Ground" and losses

[Bill Aycock]

Richard--
Is it conventional to compare the surface wave fields at a distance so near 
the Radial length and the wave length?  0.1 km Sounds like a lot, but it is 
only 100m, which is low, in  Lambda terms..
Bill--W4BSG

-----Original Message----- 
From: Richard Fry
Sent: Sunday, March 01, 2015 12:08 PM
To: topband at contesting.com
Subject: Re: Topband: Modeling "Ground" and losses

>The feedpoint connection, in all cases of vertical antennas, whether the 
>system is shunt fed or series fed, or even if it is an end-fed half wave, 
>ties one feed terminal to the ground or counterpoise system. It has to be 
>that way, and the current out into that counterpoise (whatever the 
>counterpoise is) has to be equal to the common mode current at the junction 
>flowing up into the radiator.

The link below leads to a NEC4 comparison of a 1/4WL vertical monopole using
four 1/4WL radial wires at 90-deg horizontal intervals.  In one case the
radials are buried.  In the other case they (and the monopole) are elevated
1 meter above the earth, and not connected to the earth by any metallic
path.  Applied power in both cases is 100 watts, and earth conductivity in
both cases is 5 mS/m, d.c.5.

The surface wave fields at 0.1 km from these two configurations differ by
about 1.15 dB, which means that their radiated powers differ by about 30%.

If the total energy flowing into the monopole system with buried radials is
dictated only by its hard-wired connection through the transmission line
back to the transmitter, then what is accounting for the reduction of its
radiated power?

http://s20.postimg.org/453nz5vn1/160_M_QTR_WV_MONOPOLE_Flds.jpg

R. Fry

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