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/
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Topband Reflector
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