Topbanders,
Thanks for all the replies on the ground screen query...
Having to much time, I used EZNEC 3.0 and attempted to model the various
possibilities that I can put up here in the city. Given all the possible
combinations in modeling I tried to keep things as constant and simple as
possible. I used real medium ground, no wire loss, and # 10 wire for all the
elements. Since NEC 2 does not allow buried grounds the radials were as
close as the program allows. The loads included loss (Q 300).
The antennas are;(top hats don't droop)
30' vert with 4 30' X top hats .
30' vert with 2 30' T top hats.
30' vert with 1 30'inv L top hat.
30' vert with 4 9'X top hats connected with wires at the ends
1/4 W vert, full size.
ANT Z LOAD(base) GAIN(dbi)
4 1/4 W radials;
30' X 28 205 ohm -7.66
30' T 28 285 -8.09
30' L 29 475 -8.72
30'Vert 36 1075 -13.78
30' X- 9'Con 23 300 -8.19
1/4 W 45 - -.89
50 20' radials;
30' X 13.1 170 -3.31
30' T 11.8 345 -3.59
30' L 10.5 550 -3.69
30' Vert 7.8 1140 -6.49
1/4 W 52 - .009
30 1/4 W Radials;
1/4 W 35 - 1.13
I'm not sure the results are dead on because I don't think the program takes
into account the far field response.Also, 50 and 30 are the most radials I
could get eznec to do,a real screen might be better. But the results look
like they are in the ball park. They also confirm the postings on this forum
and the replies re;the ground screen.
It appears the way to proceed is to pick up the 5 db or so from the top
loading, and then follow that up with the 4db or so from the ground
screen....Looks like I might get within 4 or 5 db of a 1/4 wave (not
counting the t/o angle difference).
Any comments as to whether I seem to be in the general area or not of
would be appreciated.
Or,that I should find something more constructive to do with my time!
Bud W0HG
|