Topband: Elevated Radials - Inverted L, Near Fld above/below ground

[Dan Maguire]

One poster on this thread mentioned a desire to compare an inverted L with elevated radials against a quarter-wave vertical with elevated radials.  Another poster mentioned looking at the near field below the surface.

I put together a ".weq" format model for use with the AutoEZ program, with all dimensions controlled by variables.  Here's a general view:

http://ac6la.com/adhoc/ElevRadInvL.gif

You can use this one model to study what happens when you change the height of the radials, the length of the radials, the length of the vertical section, and/or the length of the horizontal section.  The horizontal section length may be set to zero in which case the model becomes a simple vertical.  In the view above the radials are 130 ft (~87 deg), the vertical section is an arbitrary 65 ft, and the horizontal section has been automatically set to ~71.9 ft which produces resonance at the feedpoint.  Test frequency is 1.832 MHz.

Here's the model file:

http://ac6la.com/adhoc/ElevRadInvL.weq

If you want to play with this model using the free AutoEZ Demo program you'll have to adjust the segmentation density down to roughly 20 segments per WL from the current 100 segs per WL.

Finally, mostly just out of curiosity, here's what the near field looks like at 1 ft above ground.  This is looking straight down on the antenna.  The color scale represents E-fld intensity.

http://ac6la.com/adhoc/InvLNFat+1.gif

And here's the E-fld at 1 ft *below* ground.  This is not an apples-to-apples comparison; note the range of the scale is greatly reduced.  (NEC4 engine required to produce this view.)

http://ac6la.com/adhoc/InvLNFat-1.gif

AutoEZ (http://ac6la.com/autoez.html) works in conjunction with EZNEC v. 5.  If you prefer to use the free 4nec2 program it would be fairly simple to create an equivalent model using 4nec2 "SY" cards.  

Dan, AC6LA
http://ac6la.com/